Lighting Research & Technology

A new criterion for spectral power distribution (SPD) optimisation is proposed; this is evaluated numerically with a spectral utilisation factor (SUF). SUF is calculable on the basis of relative SPD and takes into account the luminous efficiency of (visible) radiation as well as the colour discrimination ability of the light source. The theoretical optimal light source is obtainable as a trichromatic line SPD of wavelengths 440-530-615 nm. The spectral areas of trichromatic SPD lines to optimise both SUF and colour rendering index (CRI) parameters have also been determined as 440-450 nm for blue, 530-540 nm for green and 610 nm for red lines at a spectral line (band) width of about 20-30 nm. Depending on correlated colour temperature and achromaticity requirements, various radiant intensity ratios of line (band) SPDS should be investigated for both the above criteria. The conclusions of the paper can be applied to improve the performance of practical light sources.

There is a demand for measurements of road lighting installations, both when new and periodically during their service life. In many countries such measurements are carried out only rarely, or not at all, mainly because of their laboriousness and the lack of appropriate measuring instruments. This paper presents a method and a measuring device enabling quick and easy control measurements of road lighting.

Reaction times of young adult subjects to luminous increments of various contrast were obtained at two adaptation levels. Functions characterising the data are consistent with electrophysiological recordings from cortical neurons and from the general contrast response pattern presented in other psychophysical studies. These functions help to detail some of the emerging principles of visual performance based on visual response time, and may be useful to practitioners interested in predicting the speed of performing realistic tasks.

The BRE Average Sky has recently been proposed as a means of evaluating the energy effects of new forms of daylighting design. However, the complex geometry of some innovative design solutions means that predictive calculations can be extremely difficult and direct measurement under an artificial sky may be preferred. This paper describes the outcome of a feasibility study to design an artificial sky to simulate the BRE Average Sky. The problem is essentially one of producing a particular luminance distribution within a space, and is therefore relevant to other lighting design problems where a controlled pattern of luminance is required. First the difficulties of setting up a luminance pattern are briefly discussed. These include the problems of internal reflection, and parallax errors which occur when the luminance pattern is viewed from different points within the space. Two alternative designs for the artificial sky are outlined. The first uses a specular paraboloid which can reduce parallax error considerably and causes negligible inter-reflection problems. However, it is best suited to unilateral fenestration. The second uses the more traditional matt hemisphere, but with a time-saving computer technique to optimise the simulation of the required luminance pattern. This technique could be used in a wide variety of lighting design problems, whenever a highly controlled luminance pattern is required.

Reflective dome type artificial skies are effective tools in daylight research and design, but need careful design if they are to reproduce a desired sky luminance distribution faithfully. In particular, inter-reflection within the dome can make the sky luminance distribution too uniform; the higher the dome reflectance the worse this problem is, despite a widespread assumption that high reflectance is desirable. This paper gives a general method for estimating the magnitude of this inter-reflection. It shows, for example, that a winter CIE clear sky luminance distribution cannot be obtained inside a dome of reflectance greater than 0.6. A CIE standard overcast sky can however be achieved inside a dome of high reflectance, provided considerable care is taken in the design of the rest of the artificial sky.