A review of integrative dynamic lighting and associated well-being impact for people living with dementia

Abstract

Integrative lighting considers light for both visual and non-visual impact and can therefore benefit human health and well-being. More specifically, it can benefit circadian-related well-being, an umbrella term which within dementia cohorts considers factors such as sleep, rest-activity, mood, agitation and activities of daily living. As people living with dementia experience disruptions to their circadian rhythms and spend large amounts of time indoors, the understanding of how integrative interior lighting could influence their body clock could help support their well-being. A review of 18 studies found that papers are difficult to compare due to unsystematic study designs and reporting of study characteristics, light characteristics and participant characteristics. The findings at most imply that indoor integrative lighting could be beneficial to these aspects of well-being. This review finds suggestion that for this cohort there may be a relationship between colour variation and mood and agitation, alongside a relationship between intensity variation and sleep, and that the influence on rest-activity may be more unpredictable. These findings are inferred and due to heterogeneous study designs they are inconclusive. The outcome of this review therefore recommends future studies that follow systematic checklists for study designs which seek to test these inferred hypotheses within this cohort.

1. Introduction

There is a large body of work consolidating the impact of light on well-being, particularly work which involves ‘bright light therapies’ (BLTs).^1–3 In the context of lighting studies for dementia cohorts, the authors use the term ‘well-being’ to encompass all circadian-related parameters often monitored in these studies: rest-activity, mood and depression, agitation and behaviour and sleep–wake cycles. During the last decade, several systematic reviews have highlighted the well-being implications these lighting therapies provide. Each of these reviews has focused on using varying BLTs, all of which are static in nature.^2,4,5 Results varied from finding evidence for significantly reducing depressive and behavioural symptoms,³ circadian rhythm disorders and sleep problems in dementia,⁵ to finding no conclusive evidence of BLTs being responsible for any changes in well-being.² This lack of agreement on the impact BLTs may have on well-being in dementia is evident.

However, recently, there has been a movement towards implementing integrative and dynamic lighting, as opposed to static throughout the day. This is in accordance with the observed positive effect of (dynamic) daylight on human well-being.^6,7 Following this concept, recommendations to explore the use of integrative lighting paradigms in dementia have been published from many perspectives, including lighting bodies such as the Society of Light and Lighting,⁸ dementia organisations such as the Alzheimer’s Association⁹ and research papers from chronobiologists such as Brown et al.¹⁰ Since this is a relatively recent approach to support well-being in dementia, a review of the integrative dynamic lighting experiments conducted within these cohorts is required. Therefore, this review will introduce the interdisciplinary research areas of lighting, well-being and dementia before summarising any relevant bodies of work. This review aims to summarise the body of evidence for the use of indoor lighting for well-being in dementia cohorts, with an emphasis on integrative dynamic as opposed to static interventions.

1.1 Light and well-being

Visual light is part of the electromagnetic spectrum of radiation in the range of 360 nm–400 nm to 760 nm–830 nm.¹¹ Within the lighting design industry, it has previously been reported in terms of illuminance (lux) and correlated colour temperature (CCT, Kelvin), while new metrics, SI calculators and standards for reporting light have been suggested (ENLIGHT: A consensus checklist for reporting laboratory-based studies on the non-visual effects of light in humans, CIE S 026 toolbox).^12,13

Light facilitates navigation, observation and context setting, contributing to ‘quality of life’. However, light is also capable of invoking non-visual effects on humans, which influence the body clock and regulate the body’s hormones.^14–17

Humans, like most living organisms, have an endogenous rhythm, which is known as the body’s biological clock. The master clock of this system is the suprachiasmatic nucleus (SCN) and is responsible for maintaining an approximate 24-h rhythm in accordance with daily entrainment of light; effectively aligning the endogenous rhythm with external cues such as the day/night (light/dark) cycle.¹⁸

Light is received in the retina of the eye where it reaches the intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells contain a photopigment named melanopsin which delivers these light signals to the SCN. The SCN uses light signals to regulate the body’s biological rhythm and its functions.¹⁹ One of the areas of the brain that the SCN influences is the pineal gland.¹⁵ Within this gland is the hormone melatonin; better understood as the ‘darkness hormone’.²⁰ Melatonin production peaks during the nighttime hours and is therefore critical in the regulation of the sleep–wake cycle.¹⁵ However, light causes suppression of the secretion of melatonin meaning that it can be influential on the sleep–wake cycle. These processes are not mutually exclusive but occur via separate systems and highlight that light impacts our sleep in a complex manner. In addition to this, the amount and quality of sleep that an individual receives has a secondary impact on an individual’s mood.¹⁵ In a more direct manner, light can also influence the binding capacity and production of serotonin which modulates mood.²¹ The understanding of our circadian rhythm is therefore critical in defining the relationship between light and well-being.

By definition, well-being is a multi-faceted expression, particularly when limited to describe dementia.^22,23 It is often hard to distinguish what is meant by well-being due to a lack of universal agreement; however, it is generally accepted that it encompasses the psychological welfare of a person and is not necessarily inclusive of their cognitive ability.^23,24 Many studies focus mainly on the psychological measures of mood, depression, agitation, sleep quality, ‘behaviours’ and circadian rhythms.^4,25

For people living with dementia, well-being may become compromised for several reasons. Vision deterioration with age and likely admittance to care facilities restricts them to the built environment which has less natural light. Simultaneously, artificial lighting has allowed us to extend illuminance into the night. This has disrupted the non-visual impacts that calibrate the human biological clock and may phase-shift the circadian system so that hormone stimulation can either be delayed or advanced. As a knock-on effect of this, the body clock becomes disrupted, hormone imbalance onsets and mood, sleep–wake cycles and well-being can become compromised.^18,26 It is therefore of critical importance to ensure that artificial lighting absorbed is of required parameters to entrain the circadian system. This requires sufficient intensity, timed spectral composition, spatial distribution and irradiance, as well as analysis of an individual’s historical light exposure, account of their chronotype, ethnicity, origin, age and visual impairments.²⁶ However in reality, testing all these contributions in the field is highly unfeasible and maybe even impossible. From a scientific perspective, research on the weight and importance of these constituent factors is of extreme interest.

1.2 Ageing and dementia

Dementia is a progressive neurological disorder defined by a compromise in cognitive abilities and behaviour.²⁷ It covers a range of subtypes, including the five most prevalent: Alzheimer’s Disease, Vascular Dementia, Dementia with Lewy Bodies, Frontotemporal Dementia and Mixed Dementia.^22,28 These forms of dementia arise from differing sources, but common to all is the build-up of normally soluble proteins in the brain that cause blockage of electric signals which impact memory and functioning.²⁹ It is suggested that around 50 million people in the world are living with some form of dementia at present.^30,31 Coupling this with evidence that dementia is related to ageing, and the global demographic trend is growing within older generations, there is a pending dementia crisis that could overload our healthcare resources in an already fragile system.

Over the age of 65 y, the prevalence of dementia begins to increase, with figures stating 11.1% prevalence for those aged 80 y to 84 y up to 41.1% prevalence for those aged 95 y and above.³² This means that the effects on the human body from both the process of ageing and from a dementia diagnosis need to be considered together.

By first considering the process of ageing, the human body experiences age-related deteriorations. One prevalent decline is in vision. This is due to decreasing pupil diameters, morphing of the pupil into a more irregular, non-circular structure and yellowing of the lens of the eye.^33,34 These progressive changes are increasingly prevalent in persons aged over 70 y and make it harder for the elderly eye to depict contrast sensitivities, illuminances and colour of an image.^34,35 In addition to this, elderly people are more likely to suffer from pathological changes in vision like age-related Macular Degeneration, Glaucoma or Cataract.⁴ As a result, elderly persons are at higher risk of experiencing falls which may lead to a preference to stay indoors which limits their exposures to natural light.⁴

Next, let us consider dementia. From the age of 30 y, the human brain begins to shrink, and this process accelerates from the age of 70 y.³⁵ If a person is then diagnosed with dementia, they experience accelerated cognitive decline, making everyday tasks much more difficult to achieve independently. Additionally, people living with dementia have a much more disrupted circadian rhythm than that of the typical adult, a process which suggests bidirectional influence.³⁶ Disrupted rhythms and poor sleep quality mean that the restorative properties that sleep delivers in relation to ‘mopping up’ the plaques in the brain become compromised, which further accelerates the progression of the disease.³⁶

1.3 Static versus dynamic lighting for well-being

Static lighting often refers to lighting that is fixed in terms of its colour and intensity. It appears to be composed of one colour and delivers an unchanging output throughout the day. It has been implemented in our lives since the large-scale distribution of electric lighting in the early 20th century.³⁷ In contrast, dynamic lighting is a broad term used to describe lighting that changes its spectral power distribution throughout the day. Since white light is made up of many wavelengths representing different colours, this means that the power of each unit of wavelength over a unit area varies throughout the day.³⁸ In simpler terms, this can be perceived as a change in colour and intensity of the lighting throughout the day.

Dynamic lighting is often tailored to replicate natural daylight properties, providing a stronger blue-wavelength component in the afternoon with warmer, blue-depleted components in the evenings, simulating the outdoor sky. This is important since the ipRGCs provide a peak absorption response to lighting in the blue wavelength range.¹⁹ Most recently, this type of lighting is referred to as integrative lighting.⁸

Light can also be broken down into its photopic and melanopic contributions. Photopic is a term used to describe the properties of light when referring to vision-related factors which are largely attributed to the cones in the retina.³⁹ Melanopic is a term used to describe the non-visual factors of light; in particular it describes the relative brightness for the melanopsin in the ipRGCs.¹³ Essentially, since melanopsin is the photopigment with a direct pathway to the SCN, this is a measure of the amount of lighting needed to instantiate the circadian response in the body. It is often described in terms of melanopic equivalent daylight illuminance (MEDI) lux or circadian stimulus (CS).⁴⁰ It should be noted that the ipRGCs also receive input from the visual receptors (rods and cones) so the contribution to the body’s circadian rhythm and biological effects can come from both photopic and melanopic contributions; however, a larger weight is placed on the latter. Therefore, when conducting research on the impact of integrative dynamic lighting on well-being, both photopic and melanopic contributions of the lighting need to be considered. Often, this is not the case within the literature which can make it difficult to compare study methodologies and their outcomes. However, advancements such as the recent SI-compliant toolbox developed in 2018 has made comparison of lighting paradigms used within research much more attainable.¹³ This toolbox takes into account the spectral distribution of a light source and weighs it in terms of its contribution to each of the photoreceptors in the eye (α-opic measurements).¹³ This therefore provides a translation between photopic and melanopic contributions of a light source.

The transition from static to integrative dynamic lighting has been highlighted in a paper by Gomes et al. who questioned why dynamic lighting in urban life is still the minority when health effects of daylight, which is variable, are so renowned.^41,42 This paper echoes concerns that optimum lighting exposures for circadian realignment are not yet standardised; however, it concludes that integrative dynamic lighting should be implemented as it may be more beneficial to health than static lighting.

Static light therapies such as ‘BLT’ have been used to stimulate circadian rhythms in those highly affected by circadian disruption to improve well-being. This effect is predominant in individuals with dementia. As a result, there have been positive findings from publications intended to realign these systems and improve mood and well-being.^1,4,43–46 However, notably from reviews of combined intervention studies, the use of BLT has been deemed as valuable but not concrete enough to definitively promote its application as a remedy in dementia on its own.² The therapies that were reviewed by Forbes et al.² (except one) were static, not accounting for intensity or colour variability in the throughout the day. In light of this evidence, it is suggested future research catered to the dementia demographic could benefit from incorporating a background dynamic lighting system, which is seemingly the optimum ecosystem for the circadian rhythm.

1.4 Monitoring well-being

Qualitative measurements for well-being are mainly questionnaires that have been specifically designed. Intermediary measurements are notably the Cohen-Mansfield Agitation Index, Agitated Behaviour Rating Scale, Pittsburgh Sleep Quality Index or various ‘Quality of Life’ scales which take an observed input and convert it to a globally recognised numeric scale.^47–49 Typically, qualitative measures will be combined with quantitative measures to consolidate observations of improvements in well-being.

In 2008 to 2009, the Internet of Things (IoT) was revolutionised and introduced huge capabilities for sensor technologies in the healthcare industry.⁵⁰ Consequently, the use of sensors in dementia care is not a new concept. Interestingly, and in alignment with the need for the current review, a 2017 systematic review of assistive technologies for people with cognitive impairment by Lynn et al. found that publications are sparse for lighting interventions in comparison to other assistive technologies.⁵¹ By contrast, as there is significant evidence for the benefits lighting can have on well-being in persons with disrupted circadian systems, the need to quantify optimum lighting parameters to establish optimum intervention design is imminent.

To date, studies largely employ similar technologies to measure quantitative well-being parameters during interventions. Reports commonly include wrist actigraphy to measure ADLs, motor ability and sleep routines, accelerometers to measure sleep–wake cycles and agitation, remote passive infrared (PIR), video camera and acoustic sensors to measure mobility, falls and activities of daily living (ADLs), which can also be linked to cognition.^52–55

However, the sensing process can be made difficult due to issues like feasibility of wearables in long-term studies, data connection issues, data privacy and security compliance, technology acceptance, person-specific requirements for technology, assumptions made in analysing or categorising data among others.^{51,52,54,56–58} As a result, gaps in technology design currently demand future iterations to seek out expertise from multiple stakeholders to include clinicians, manufacturers and academics, in order to create a more integrated care approach.

2. Method

The search process for this review is aligned with the PRISMA Research Process Flow Diagram.⁵⁹ The search took place on 16th January 2024 in five relevant databases: Scopus, Medline, Embase, Google Scholar and PsycINFO. The refining search conditions applied to each of the databases were the same and included the following:

Search terms: (circadian OR clock OR rhythm OR biorhythm OR chronotype) AND (dementia OR Alzheimer’s OR cognitive decline) AND (lighting OR luminaire OR integrative lighting OR dynamic lighting OR tuneable lighting) AND (well-being OR quality of life)

Years: 2008 to present

Language: English

This review focuses on the specific interlinking areas of integrative dynamic lighting interventions applied to dementia cohorts. The search was limited to the past 15 years of publications since the IoT revolution and improved sensing paradigms were introduced here, and a review leveraging results from multi-modal (sensing techniques) are favoured. As such, the search process returned a total of 18 studies meeting this inclusion criteria as seen in Figure 1.

Figure 1

PRISMA flow chart

3. Results

The current review returned 18 papers relating to integrative dynamic lighting paradigms applied to people living with dementia, as seen in Supplemental Table S1. The methods for deploying this lighting varied. Many studies applied mounted or ceiling-suspended luminaires^{60–62,66–68,74,76} or used floor lamps.^{63–65,69–73,75} A combination of floor lamps, light boxes and light tables were chosen by Figueiro et al.⁴⁰

Lighting interventions were usually provided in both common areas and bedroom areas.^{40,69–72,75} In one study, integrative dynamic lighting was only provided in the bedroom,⁶² and in some other studies it was limited to living areas only.^65–68,73 The remaining studies only deploying in common areas.^{60,61,63,64,74,76}

Nine of the studies recorded the subtype of dementia,^{60,62,64–66,68,71–73} while only four explicitly recorded the state of progression of dementia for each participant.^40,62,65,66

Common to all publications was the use of qualitative or intermediary observational measures to depict well-being, with ten studies consolidating this with metrics derived from sensing technologies.^{40,61–63,66,68,69,71,74,76} The largest number of subjects recruited was by Kolberg et al.⁶⁷ and Hjetland et al.⁶⁸ with 69 people from four different healthcare settings, and they also employed some of the longest continuous exposure durations to integrative dynamic lighting focusing around the six-month marker alongside Figueiro et al.,⁴⁰ Kolberg et al.⁶⁶ and Saidane et al.⁷⁰

In terms of well-being parameters assessed, eight studies had different focal points combining multiple aspects of well-being^{40,60–62,69,71,74,76} with the remaining ten studies focusing on one well-being aspect alone.^{63–68,70,72,73,75} Notably, 14 of the 18 studies demonstrated some measurable extent of positive influence to well-being after integrative dynamic lighting exposure.^{40,60–64,67–72,74,76}

In terms of mood and depression, seven studies measured this factor of well-being. Bromundt et al.⁶² found that inducing a dawn–dusk simulation based on the illumination at the equator in spring equinox led to statistically significant improvements in mood and cheerfulness in the morning during the second four weeks of the eight-week dawn-dusk simulation (DDS) intervention. Similarly, Kolberg et al.⁶⁷ found improvements to mood over a 16-week period after daylight simulation with a mean MEDI of 779 lx.

Van Lieshout-van Dal et al.⁷¹ found significant improvements to depression after two four-week intervention periods using integrative dynamic lighting ranging from MEDI = 850 lx at 07.30 to a peak of MEDI = 1700 lx during the afternoon and MEDI = 300 lx in the evening. Figueiro et al.⁴⁰ found a significant reduction in depressive symptoms arose from targeting a CS of 0.4 with cool white CCT after 25 weeks. Finally, van Lieshout-van Dal et al.⁷² found that using colour temperatures of 4000 K to 3000 K from 09.30 to 17.30 and varying MEDI intensity from 850 lx to 1700 lx to 650 lx prompted 100% of users to believe that the integrative dynamic lighting in the living room was positively impacting their overall well-being. However, Juda et al.⁷⁴ found that there was no change in depressive symptoms after a five-week control/intervention using MEDI = 545 lx and cool colour temperatures for most of the day and MEDI of 163 lx to 46 lx and warm temperatures in the evenings.

Measurements of sleep and nighttime activity were demonstrated in studies by 9 out of 18. Van Lieshout-van Dal et al.⁶³ found a statistically significant reduction in the frequency of nighttime disturbances and an increase in total sleep time after a total of 63 days exposure to integrative dynamic lighting in common areas. A MEDI level up to 695 lx was provided while varying the colour temperature from cool in the day and warm in the evenings. Saidane et al.⁷⁰ also found a reduction in nighttime activity after six months of exposure to integrative dynamic lighting. Figueiro et al.⁴⁰ found a significant reduction in sleep disturbances after 25 weeks with colour temperatures in the blue spectrum (4000 K to 6000 K). Interestingly, this effect was confirmed from both observations and sensory techniques but with an evident latency in the result from the sensory methods, indicating that the former may act as a predictor of the latter monitoring tool. Hjetland et al.⁶⁸ found after 16 weeks and 24 weeks that proxy-measured sleep significantly improved; however, this was not replicated in the actigraph measurements. Similarly, van Lieshout-van Dal et al.⁷¹ found that there was no significant difference in minutes of rest per night after four weeks of exposure to integrative dynamic lighting varying up to MEDI = 1700 lx and with a cool/warm spectrum. Bromundt et al.⁶² did not find any significant changes to sleep/wake cycles after the dawn–dusk simulation employed over eight weeks. Interestingly, Giggins et al.⁷⁶ also found no improvement to sleep after integrative dynamic lighting exposure over four weeks with constant MEDI but varying CCT but a slight improvement in the non-intervention group. Juda et al.⁷⁴ found no change in sleep parameters measured after five weeks of integrative dynamic lighting exposure ranging from MEDI = 46 lx to 545 lx and warm/cool colour temperatures. Linander et al.⁷⁵ also found no impact on sleep after eight weeks of integrative dynamic lighting of constant illuminance but varying CCT.

Changes in agitation were reported in 6 out of 18 studies. Wahnschaffe et al.⁶¹ found that after four months of integrative dynamic lighting exposure, up to MEDI = 1474 lx in the morning and MEDI = 45 lx in the evening with a change in CCT from 4440 K to 6500 K resulted in a statistically significant reduction in the amount of agitation, particularly for non-aggressive behaviours. van Lieshout-van Dal et al.⁶⁴ found a decrease in the severity of 7 out of 12 neuropsychiatric conditions including agitation after exposure to constant MEDI of 379 lx to 695 lx to 379 lx from morning, afternoon and evening with cool-to-warm colour temperatures. Saidane et al.⁷⁰ found that the frequency of agitated expressions reduced after the six-month intervention with colour temperatures changing from cool to warm in afternoon to evening; however, the variation in MEDI lux was not stated. van Lieshout-van Dal et al.⁷¹ found a reduction in agitation after eight weeks of exposure to integrative dynamic lighting up to MEDI = 1700 lx with varying colour temperatures from cool in the morning and warm in the evening. Figueiro et al.⁴⁰ found a significant reduction in agitation in severe dementia cohorts during weeks 3, 9, 17 and 25 of integrative dynamic lighting exposure. Interestingly, Bromundt et al.⁶² found no significant change in agitation after dawn–dusk simulation, but those who were less cognitively impaired expressed more agitation than those with a more progressive disease. These latter two studies seem to find that the impact of integrative dynamic lighting has more of a positive effect on those with a more severe progression of dementia.

Of the eighteen studies, four studies showed no change to any impact of well-being. Linander et al.⁷⁵ found no change to sleep, Aarden-van Delft et al.^65,73 found no change to ADLs and Kolberg et al.⁶⁶ found significant differences in rest-activity that were no longer significant after false discovery rate (FDR) correction.

It is very difficult to compare the impact of existing studies due to the discrepancy between the use of illuminance/colour change and the units of measurement used in reporting. Additionally, the response to lighting is largely unpredictable within an inter-individual basis. Table 1 demonstrates the available information regarding exposure timings/durations and range in MEDI used for each study. This table demonstrates the observable missing or unspecified data in multiple studies, making comparisons for an already small pool of papers difficult. Nevertheless, Table 1 can be used to note any similarities in studies with reported outcomes as a means to guide this review of studies.

Table 1

Comparison of lighting parameters for each of the review studies from Supplemental Table S1

Author, Year	Wholly dynamic?	Largest transition in MEDI (lx)	Programmed lighting timing	Longest duration at highest illuminance (h)	Longest duration at lowest illuminance (h)	Duration at highest CCT (h)	Duration at lowest CCT (h)
Sust et al., 2012⁶⁰	Y	1068	06.00 to 18.00	8	2	10	2
Wahnschaffe et al., 2017⁶¹	Y	1429	05.00 to 20.00	5	1	5	5
Bromundt et al., 2019⁶²	N	81.78	06.00 to 09.00 then 22.00 to 23.00	Approx. 1	1	Unspecified	Unspecified
Giggins et al., 2019⁷⁶	N	0	09.00 to 20.00	Unspecified	Unspecified	6	5
van Lieshout-van Dal et al., 2019⁶³	Y	316	07.30 to 22.30	4	5.5	Approx. 2.5	Approx. 1.5
Van Lieshout-van Dal et al., 2019⁶⁴	Y	316	07.30 to 22.30	4	5.5	Approx. 2.5	Approx. 1.5
Figueiro et al., 2020⁴⁰	N	Unspecified	06.30 to 18.00	Unspecified	Unspecified	Unspecified	Unspecified
Juda et al., 2020⁷⁴	Y	499	06.00 to 20.00	10	Approx. 1	10	Approx. 1
Linander et al., 2020⁷⁵	N	0	07.00 to 21.30	Unspecified	Unspecified	2	3.5
Baandrup et al., 2021⁶⁹	Y	Unspecified	07.00 to 22.00	Approx. 1	Unspecified	Approx. 1	Unspecified
Aarden-van Delft et al., 2021⁶⁵	Y	569	All day	Unspecified	Unspecified	Unspecified	Unspecified
Hjetland et al., 2021⁶⁸	Y	Approx. 380	07.00 to 21.00	5	3	5	3
Kolberg et al., 2021⁶⁶	Y	Approx. 380	07.00 to 21.00	5	3	5	3
Kolberg et al., 2021⁶⁷	Y	Approx. 380	07.00 to 21.00	5	3	5	3
van Lieshout-van Dal et al., 2021⁷²	Y	850	07.00 to 21.00	6	1.5	0.5	1.5
Saidane et al., 2022⁷⁰	Y	Unspecified	07.00 to 22.00	Unspecified	Unspecified	Unspecified	Unspecified
Aarden-van Delft et al., 2023⁷³	Y	569	All day	Unspecified	Unspecified	Unspecified	Unspecified
van Lieshout-van Dal et al., 2023⁷¹	Y	850	07.00 to 21.00	6	1.5	0.5	1.5

‘Unspecified’ refers to studies where details were not published or did not clarify estimated exposures.

4. Discussion

The results of the review have been grouped into four sections for discussion according to the well-being parameter impacted, including sleep measurements, mood and depression, ADLs and rest-activity, and agitation and behaviour.

4.1 Sleep measurements

Of the nine studies that measured sleep parameters, four showed promises in being able to reduce sleep problems and/or improve sleep quality^40,63,68,70 and five showed no significant change after exposure to various integrative dynamic lighting paradigms.^{62,71,74,75,76}

Of the studies that found positive impacts, common to all was the change in both the intensity and the CCT of the lighting throughout the day, making them ‘wholly dynamic’ interventions. In contrast, only two of the studies that found there was no significant change in sleep parameters used ‘wholly dynamic’ lighting, with the remaining three using solely a change in CCT or a change in lighting intensity throughout the day. In a recent study by Blume et al.,⁷⁷ the authors tested the impact of different colour lighting on the circadian rhythm and found that ‘light colour is less important for the internal clock than originally thought’. This stands to reason that changing both lighting parameters may be required to achieve any positive impact to sleep. This is in agreement with certain daylight studies (daylight being wholly dynamic) by Flores-Villa et al.⁷⁸ which have demonstrated that more exposure to daylight in summer compared to winter resulted in an improvement to subjective sleep quality in the ageing population. However, there are some studies that have found improvements to sleep using bright light treatments which deliver high intensity lighting in shorter term bursts up to several hours a day. For example, in a study by Sekiguchi et al.,⁷⁹ there was an improvement to sleep disturbances in 50% of Alzheimer’s participants after two weeks exposure to morning bright light for one hour a day; however, this impact was not observed for participants with different subtypes of dementia. This type of lighting is not dynamic in nature yet still provided benefits to some participants. It may be that the positive impact would have been extended to more of the cohort if they also employed lower intensity and/or warmer lighting in the evenings. This would be in agreement with a study by Shishegar et al.⁸⁰ who found a significant increase in the total sleep time for older adults after both varying illuminance and CCT lighting and with varying illuminance and fixed warm lighting in the evenings (2700 K).

Another compelling piece of evidence is the impact that the total length of the integrative dynamic lighting intervention has on sleep. Of the four studies demonstrating positive impact, their total duration of exposure to integrative dynamic lighting lasted between an estimated 63 days and 180 days, respectively. In contrast, the five studies which showed no change had total exposure durations between 28 days and 56 days, respectively, which is considerably shorter across the board. This stands to reason that the longer the exposure duration to integrative dynamic lighting, the more likely it is to have a positive impact on sleep for people living with dementia. This is in agreement with a direct study preluding Figueiro et al.⁴⁰ that highlighted the amplification in positive impact observed on sleep characteristics over longer durations of exposure.

By leveraging the information in Table 1 in terms of sleep, two of the four studies which reported the transition in MEDI and demonstrated a positive impact on sleep reported an MEDI range of 316 lx and 380 lx, respectively.^63,68 In contrast, of the five studies that reported no change in sleep, the largest transition in MEDI was 850 lx, 81.78 lx, 0 lx, 499 lx and 0 lx, respectively.^{62,71,74–76} If we consider the 2022 consensus published by Brown et al.,¹⁰ it highlights the light exposure recommendations for typical populations. A minimum MEDI of 250 lx is recommended during the day with a significant reduction in illuminance approximately three hours before bedtime.

Therefore, it would stand to reason that three of the five studies which observed no change in sleep did not have a large enough transition in MEDI to attain any impact. For the other two of these studies, the transition in MEDI during the day would have been appropriately large to instantiate an impact on sleep; however, the longest duration of lighting at lowest illuminance was 1 h to 1.5 h, respectively, in comparison to the 3 h to 5.5 h, respectively, for the positive impact studies. This highlights that the reduction in illuminance of the lighting before bed as indicated by Brown et al.¹⁰ plays a significant role in improving sleep for people living with dementia as well. Furthermore, these last two studies changed both colour and intensity of the lighting, while the other three which had no impact changed either intensity only or colour only, respectively.^62,75,76 Since the illuminance range for Bromundt et al.⁶² (intensity only study) was not large enough to instantiate an impact on sleep, it stands to reason that CCT alone may not be sufficient enough to provide a positive influence over sleep. This is in agreement with a recent study by Blume et al.⁷⁷ documenting that exposure to white, blue and yellow lighting in typical adults in the evening made no difference to measured sleep parameters.

4.2 Mood and depression

Of the seven studies measuring mood and/or depression, five demonstrated a positive impact^{62,64,67,71,81} one demonstrated no significant change⁷⁴ and one demonstrated both positive and negative impact to mood.⁷⁶

One of the studies which stands out is Kolberg et al.⁶⁷ which found a significant improvement in mood from baseline to 16 weeks, but this effect was not witnessed at the additional milestones at weeks 8 and 24. Lack of improvement at the four-week baseline aligns with a study by Al-Karawi and Jubair⁸² which highlighted that alleviating depression using light therapies usually takes two to five weeks to take effect. Similarly, Figueiro et al.⁴⁰ found a cumulative decrease in depressive symptoms throughout the experimental process as exposure duration of integrative dynamic lighting is increased. This is in contrast to the lack of improvement observed by Kolberg et al.⁶⁷ after 24 weeks of exposure. Since both studies used similar exposure durations, this suggests that either the difference in lighting parameters used and/or the inter-individual difference of circadian rhythms/chronotype may have played a larger role on well-being. Additionally, the 24th week would have fallen during the Spring season, meaning that the environmental contrast in control and intervention exposure groups may not have been as vast as in earlier weeks during Winter and may have contributed to the absence of any impact to mood at this time.

The balance in exposure duration of high versus low CCT seems to play an important role in influencing mood and depression. From Table 1, all the studies that found improvements to mood and/or depression used comparable lengths of time under both peak and minimum CCT. In contrast, the one study that did not report any change implemented 10 h at highest CCT compared to approximately 1 h at lowest CCT.⁷⁴ This leads us to conclude that the colour balance of the lighting throughout the day may be a more sensitive parameter to consider when used to improve mood and depression within this cohort. This is in agreement with a study by Shishegar and Boubekri⁸³ who used two conditions (1: changing both illuminance and colour, 2: changing illuminance only) on healthy adults and found that the former condition exhibited significantly larger improvements than the latter. This validates the evidence that a transition in CCT of the lighting may also be required to instantiate this improvement to mood and depression for people living with dementia.

Interestingly, five of the seven studies that measured mood and/or depression also monitored sleep as a well-being parameter. Tuning sleep–wake cycles has been proven to modulate mood (see Boivin et al. ⁸⁴) which could explain the positive findings between these parameters of well-being in Figueiro et al.⁴⁰ However, due to the fact that the colour of the lighting does not seem to be as influential a parameter on sleep (see Section 4.1) as it is for mood, perhaps this could explain why mood alone was impacted in the study by Bromundt et al.⁶² Notably, this complex relationship makes ‘prescribing’ lighting for supporting multiple parameters of well-being a very challenging request. As the pool of studies is small, it is difficult to conclusively determine if impacts observed due to integrative dynamic lighting are causal in nature. For example, from the studies monitoring mood/depression in Supplementary Table S1 and Table 1, the amount of MEDI used throughout the day varies from 0 lx to 850 lx, and positive implications are seen across this scale. Supplementary Table S1 highlights that the one study that observed no difference in this parameter had a lighting intervention that was carried out in areas that excluded the bedroom. In contrast, of the five positive studies, four were conducted in areas that included the bedroom. If a parallel could be drawn between these variables, it could indicate that integrative dynamic lighting needs to be completely ambient to have maximum impact or that (by default) people living with dementia spend a considerable amount of time within their bedrooms, thereby subjecting themselves to a more unintentional ambient lighting environment.

4.3 ADLs and rest-activity

Regarding ADLs and rest-activity, ten papers published findings; five of which producing an improvement^{60,62,69,74,76} and five reporting no change to ADLs or rest-activity.^{40,61,65,66,73} Sust et al.⁶⁰ found more frequent participation in activities like setting the table and folding laundry after exposure to integrative dynamic lighting with a maximum MEDI transition of 1068 lx, specifically with higher illuminance leading to more participation in social activities in the afternoon. This is in agreement with a study by van Someren et al.⁴⁵ which monitored rest- activity disturbances in people with severe dementia and reported improvements corresponding to all-day increased illumination. Similarly, this is in agreement with a study by Riemersma et al.¹ which highlighted a reduction in deterioration of ADLs after two years of all-day BLT, which is related to reduction in deterioration of cognitive decline. This seemingly points towards higher illuminances being impactful for ADLs in dementia. However, Bromundt et al.⁶² used a maximum transition and maximum MEDI of 81 lx and found a positive impact to circadian stability which would indicate that higher illuminance is not always required to impact rest-activity. Perhaps the difference between these studies is that rest-activity is highly interlinked with sleep–wake cycles, and the intervention by Bromundt et al.⁶² took place in the resident’s bedroom compared to solely common areas in the studies by Sust et al.^60,62 Additionally, both studies^60,62 refer to large heterogeneity in inter-individual rest-activity patterns and mobility which may have been influenced by the progressive state of dementia. To reiterate, these cohorts were not separated in these studies so inference of specific relationships cannot be made.

Figueiro et al.⁴⁰ and Aarden van Delft et al.⁶⁵ also monitored ADLs, and both found no significant changes to ADLs after exposure to integrative dynamic lighting. The latter of the two studies however found a stabilisation in ADLs in two out of three participants after a 5.5-month period suggesting that integrative dynamic lighting may be able to slow down the reduced capacity for performing ADLs as the neurodegenerative characteristics of the disease progress. Again, this theory would be in agreement with studies such as Riemersma-Van der Lak et al.¹ who found that the reduction in rate of cognitive decline was maintained on the longer term over a two-year study using BLTs. However, the measurement of ADLs before and after integrative dynamic lighting therapies is less frequently monitored and reported, and it is therefore difficult to conclude if the effects seen are directly related to the lighting contributions received.⁸⁵

The papers in this review that reported on ADLs and/or rest-activity did not have consistent intervention parameters that produced improvements to well-being, making it very difficult to draw causal conclusion. For example, positive implications were found in studies that were both wholly dynamic^60,69,74 and intensity or colour changing only.^62,76 Within these studies, some included bedroom fittings and some did not and the illuminance used ranged from very low⁶² to very high.⁶⁰ Moreover, the balance in the duration of exposure to opposing CCTs (cool vs warm) or opposing intensities (low vs high) as seen in Table 1 are also varied, with positive implications observed for all scenarios. It therefore seems that the integrative lighting interventions required to support rest-activity and ADLs for people living with dementia are unpredictable at present.

4.4 Agitation and behaviour

Regarding agitation and behaviour, six reported positive findings^{40,61,64,67,70,71} and one reported no change after exposure to integrative dynamic lighting.⁶²

Common to all the studies that found positive implications to well-being was the deployment location. All studies had light fixtures in common areas or living areas with some also including bedrooms. In contrast, Bromundt et al.⁶² solely deployed lighting in the bedroom vicinity. An explanation for the lack of improvement observed in the latter study could be due to the fact that people living with dementia often experience sundowning in the evening hours as the sun goes down. Since their study took place over Winter when the sunset may be at dinner time, it could be that residents were still in the common areas during sundowning hours so were not experiencing the bedroom lighting during these times. Alternatively, the study by Bromundt et al.⁶² used varying MEDI up to 81.78 lx for a short period of time in the early morning and late evening. Since five of the six studies that observed a reduction in agitation frequency or severity used wholly dynamic lighting including a variation in CCT throughout the day, it could be that the colour of lighting contributes in a more significant manner than intensity alone with regard to agitation for this cohort. This is in agreement with studies by van Hoof et al.⁸⁶ who implemented integrative dynamic lighting and demonstrated a decrease in non-physical aggression. Furthermore, there are studies which have used darkness therapy as a method to reduce symptoms in people who experience manic episodes. In a randomised controlled trial using blue-blocking wavelength glasses from 18.00 in the evening to 08.00 in the morning for one week, the study found that there was an immediate reduction in irritability within the first day within the intervention group.⁸⁷

Furthering this evidence of colour variation providing a large significance in reducing agitation are the numerous ‘BLTs’ that have observed detrimental implications to the parameter of agitation in these cohorts. For example, a study by Barrick et al.⁸⁸ reported an increase in agitated behaviours during morning, all-day and evening BLTs, especially in mild-moderate dementia cohorts, with more severe cohorts becoming more agitated under morning light therapies. This is aligned with the 2014 review by Forbes et al.² which reported no significant findings of BLTs influencing agitation, with one study by Lyketsos⁸⁹ which used one-hour exposure to morning BLT over four weeks actually demonstrating worsening in the symptoms of agitation in five participants. Although it is convenient to assume that higher illuminance lighting is the cause of this increased agitation, this is not the case. Two of the studies in this current review Wahnschaffe et al.⁶¹ and van Lieshout-van Dal et al.^71,72 used MEDI transition of 1429 lx and 850 lx, respectively, which would be considered ‘bright light’ and found positive implications on agitation. However, both studies are wholly dynamic and varied CCT throughout the day, further deducing that CCT must play a vital role on reducing agitation in dementia. Moreover, to reduce the likelihood for agitation to be heightened due to lighting, the removal of blue-heavy lighting influence in the evening and night is seemingly becoming an evidence-based design requirement.⁸⁷

4.5 Summary

Table 2 summarises the integrative dynamic lighting paradigms which have mainly provided positive implications to each of the monitored well-being parameters. It demonstrates a general trend observed from the 18 studies and is not intended to be used as validated recommendations.

Table 2

Inferred trends observed for integrative lighting impact on dementia well-being parameters

Sleep	Mood (and/or) depression	ADLs (and/or) rest-activity	Agitation (and/or) behaviour
Combining CCT and intensity variations seemingly produces better sleep outcomes. The intensity of the lighting is seemingly more significant for sleep than colour change is. The length of studies implementing integrative lighting should seemingly be more than two months to observe impact. Increasing the duration of exposure to low intensity lighting near bedtime to 3 h to 5 h seemingly improves sleep outcomes.	Combining CCT and intensity variations seemingly produces better mood and/or depression outcomes. Providing integrative dynamic lighting in all areas including the bedroom seemingly provides more observations of improvement to mood. Balancing the number of hours of exposure at high and low CCT seemingly provides more observations of improvement to mood.	Integrative lighting parameters provided a vast range and somewhat inconclusive findings in relation to impact on ADLs and/or rest-activity for this cohort.	Combining CCT and intensity variations seemingly produces better agitation and/or behaviour outcomes. Integrative lighting in common areas or areas a resident is likely to frequent during sundowning hours is seemingly beneficial for reducing agitation. This may be more relevant in shorter winter days. The CCT of the lighting is seemingly more significant for agitation/behaviour than intensity is.

These highlight possible hypotheses to test in future studies.

From Table 2, it is evident that prescribing lighting for improving multi-faceted well-being in dementia is extremely difficult. There are some lighting parameters that weigh more importance for sleep that are in contrast to those for supporting mood for people living with dementia. This is not indicative of a lighting paradigm not being beneficial for one parameter over another, but instead amplifies the requirement for more studies in order to complete a more fully informed comparison.

5. Future work and limitations

Possibly the most important takeaway from this review is the fact that study designs surrounding this research are chaotic and often incomparable. There is a need to standardise the reporting methodology so that results from independent studies can be comparable. As of 2024, the ENLIGHT checklist has been made publicly available and outlines the guidelines for lighting studies and their reporting criteria.¹² From the findings in this review, it is recommended that all future studies follow this checklist which ensures all participant details, study characteristics, measurement level characteristics and light characteristics are systematically disclosed. In this review, the studies by Hjetland et al.,⁶⁸ Kolberg et al.⁶⁶ and van Lieshout-van Dal et al.⁷² were the most robust in terms of reporting these requirements.

Additionally, the 2024 CIE Position Statement on Integrative Lighting can be used as a guide when designing lighting studies as it states the recommendations for the plane of measurement, minimum exposure illuminances for typical adults and future research pathways in this field.⁹⁰ Most importantly, it directly quotes that ‘funding bodies should prioritise projects that will provide information about more diverse samples varying in age and health status’. This amplifies the importance of bettering our understanding of the impact of light on the well-being for people living with dementia, and in conjunction with this review it really brings to the forefront the absence of knowledge that exists at present.

Integrative dynamic lighting has evidently produced largely positive implications on well-being in persons with dementia; however, the heterogeneity of lighting designs makes comparison of responses more difficult. One of the longest continuous studies was 25 weeks, which demonstrated the time dependency of positive changes to well-being.⁴⁰ This highlights the importance of continuous, longer-term research in uncovering the relationship between light and well-being.

Understanding of the optimum integrative dynamic lighting for alleviating symptoms in dementia is seemingly more solid for individual well-being parameters, with conflicting results exhibited when measuring multiple parameters under the same lighting parameters. Many studies focus on monitoring sleep parameters, but science suggests this is heavily interlinked with mood, hormones and circadian rhythm so interlinking of studies should be undertaken. Furthermore, there is a need for interventions to be completely ambient, with luminaires in all areas residents occupy. Indeed, at a minimum, all study designs should report the spectral power distribution of the lighting so that even in the absence of melanopic information being reported, this can be calculated using SI calculator tools such as the CIE toolbox.¹³ The lack of quantitative sensing metrics used to consolidate observations may be detrimental to progress in this field. Lastly, the papers analysed in this review suggest integrative dynamic lighting has a more positive influence within cohorts with more severe dementia, which is in contrast to suggestions from the 2014 review, highlighting the need to put into practice what has been repetitively demanded from researchers in this field; better stratification of cohorts.²

The range in latitude of the study locations was 40°N to 60°N, with Bergen in the Norway being the northernmost point. These are considered mid-latitude studies. Higher latitude countries have different natural light exposures, and as the importance of previous light history and exposure have been observed to influence the forthcoming lighting interventions, incorporation of latitude-specific needs should be considered for future studies. Resultantly, it would be beneficial to ensure such studies would differentiate between people who have lived at high latitudes their entire lives versus people who have moved there at a particular stage of their life.

One final limitation is that the authors have made inferences on how light may impact well-being for people living with dementia while being aware of the fact that some studies have not disclosed types of dementia, plane of measurement and other factors from the ENLIGHT checklist. At most, the author’s synthesised observations may provide baseline hypotheses for future lighting studies which will have more regimented study designs. The authors note that their conclusions are somewhat inferred and that they are worth exploring in further detail in future studies.

6. Conclusion

A review was conducted to generate insight into the impact of integrative dynamic lighting for supporting well-being for people living with dementia. The papers returned from the search were difficult to compare due to unsystematic study designs, reporting of study characteristics, light characteristics and participant characteristics. Therefore, the findings at most imply that integrative dynamic lighting could be beneficial to well-being in relation to aspects of sleep, mood, agitation and ADLs/rest-activity. Moreover, this review suggests that colour variation could be seemingly more important for supporting mood and agitation, intensity variation could be seemingly more influential for supporting sleep, and lighting influence on rest-activity could be seemingly more unpredictable within these cohorts. The authors recommend exploring these hypotheses in future studies with more robust and comparable study designs.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

K Turley

Supplemental material

Supplemental material for this article is available online.

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