The application of CRF to office lighting design

Abstract

Veiling reflections reduce task visibility and may cause visual discomfort. They can be quantified by the Contrast Rendering Factor (CRF). The factors determining the magnitude of the CRF are each dealt with in turn using data derived from various published studies. The presence of a high luminance in the offending zone is shown to be the chief cause of low CRF. A minimum CRF standard of 0.7 for written tasks on matt or semi-matt paper is proposed for offices. The calculation and measurement of CRF is briefly discussed and a simple method of field measurement suggested. Some general guidelines for good CRF design are proposed. The use of a small number of efficient luminaires arranged in a regular linear array in a room with high reflectance surfaces, together with low specularity visual tasks, is advocated.

Get full access to this article

View all access options for this article.

References

Cie Publication 19. A unified framework of methods for evaluating visual performance aspects of lighting . Commission Internationale de l'Eclairage (1972).

Uitterhoeve, W. and Kebschull, W. , Visual performance and visual comfort in offices, Second European Light Congress , Brussels (September 1973).

Bjørset, H.H. and Frederiksen, E. , A proposal for recommendations for the limitation of the contrast reduction in office lighting, Proc CIE 20th Session, Kyoto ( 1979).

Reitmaier, J. , Some effects of veiling reflections in papers . Ltg. Res. & Technol., 11, (4), 204-209 (1979).

Boyce, P.R. , The variability of contrast rendering factor in lighting installations , Ltg. Res. & Technol., 10, (2), 94-105 (1978).

Slater, A.I. , Variation and use of contrast rendering factor and equivalent sphere illuminance , Ltg. Res. & Technol. , 11, (3), 117-139 (1979).

Blackwell, H.R. , DiLaura, D.L. and Helms, R.N. , Application procedures for evaluation of veiling reflections in terms of ESI, Jnl. Illum. Eng. Soc. (USA), 2, 299-327 (1973).

Lewin, I. , An ESI study for different tasks. Jnl. Illum. Eng. Soc. (USA), 6, 44-51 (1976).

Blackwell, H.R. , Measurement of the contrast rendition factor for pencil handwritten tasks. Illum. Eng., 65, 199-210 (1970).

10.

Boyce, P. R., Veiling reflections: An experimental study of their effects on office work, ECRC/M1230. Electricity Council Research Centre (1979).

11.

De Boer, J.B. , Performance and comfort in the presence of veiling reflections. Ltg. Res. & Technol., 9, (4), 169-176 (1977).

12.

12 Personal communication, Kyoto.

13.

DiLaura, D.L. and Stannard, S.M. , Instrument for measurement of equivalent sphere illuminance, Jnl. Illum. Eng. Soc. (USA), 7, (3), 183-189 (1978).

14.

Delaney, W.B. , Fredricksen, J.A. and McNelis, J.F. , Using the ESI meter in lighting applications , Jnl. Illum. Eng. Soc. (USA), 8, (4), 229-234 (1979).

15.

Boyce, P.R. , The contrast rendering factor and office lighting, ECRC/R1133. Electricity Council Research Centre (1978).

16.

Cuttle, C. and Slater, A.I. , A low energy approach to office lighting, Light and Lighting , 68, 20-25 (1975).