1. ARC 252 : Lighting & Acoustical Design Department of Architecture I BRAC University 1ARC 252 : Lighting & Acoustical Design COLOR Rendering

2. ARC 252 : Lighting & Acoustical Design2 Although light sources may have the same color appearance, this doesn’t necessarily mean that colored surfaces will look the same under them. Two lights that appear the same white, may be the result of different blends of wavelengths.

3. And since the surface may not reflect the constituent wavelengths by the same extent, its color appearance will change when it is exposed to one or other light. A piece of red cloth will appear ‘true’ red when seen illuminated by white light produced by a continuous spectrum, but in an equally white looking mixture of yellow and blue light it will look greyish brown. Because of the absence of red wavelengths, there is no red for the cloth to reflect into the eye to notice. ARC 252 : Lighting & Acoustical Design3 Color Rendering

4. ARC 252 : Lighting & Acoustical Design4 is an important criterion when selecting light sources for lighting application solutions. To classify light sources on their color rendering properties the so called color rendering index (CRI or also denoted as Ra) has been introduced. The scale of the Ra ranges from 50-100. The following table shows the meaning of the Ra values: Ra = 90 - 100 Excellent color rendering properties Ra = 80 - 90 Good color rendering properties Ra = 60 - 80 Moderate color rendering properties Ra < 60 Poor color rendering Color Rendering

5. ARC 252 : Lighting & Acoustical Design5 Color Temperature

6. ARC 252 : Lighting & Acoustical Design6 Although white light is a mixture of colours, not all whites are the same since they depend on their constituent colours. So a white with a higher proportion of red will appear warmer and a white with a higher proportion of blue will appear cooler. In order to classify the different types of white light, the concept of colour temperature is applied which is described as the colour impression of a perfect black- body radiator at certain temperatures.

7. This concept can be best explained with the help of familiar thermal radiators like the filament of an incandescent lamp or an iron bar. When these materials are heated to a temperature of 1000 K their colour appearance will be red, 2000-3000 K they will look yellow white, 4000 K neutral white, and 5000-7000 K cool white. In other words: the higher the colour temperature, the cooler the impression of the white light becomes. ARC 252 : Lighting & Acoustical Design7

8. 8

9. 9

10. 10

11. ARC 252 : Lighting & Acoustical Design11

12. ARC 252 : Lighting & Acoustical Design12

13. ARC 252 : Lighting & Acoustical Design13

14. ARC 252 : Lighting & Acoustical Design14

15. ARC 252 : Lighting & Acoustical Design15

16. ARC 252 : Lighting & Acoustical Design16

17. ARC 252 : Lighting & Acoustical Design17

18. ARC 252 : Lighting & Acoustical Design18

19. ARC 252 : Lighting & Acoustical Design19

20. ARC 252 : Lighting & Acoustical Design20

21. ARC 252 : Lighting & Acoustical Design21