enlarging the pupil, allowing more light to enter the eye. ... Source: IESNA
Lighting Handbook, 9th Edition, (New York; IESNA, 2000), 27-4. www.lutron.com.
Measured light vs. perceived light Measured light vs. perceived light The The human human eye eye responds responds to to low low light light levels levels by by enlarging the pupil, allowing more light to enter enlarging the pupil, allowing more light to enter the the eye. eye. This This response response results results in in aa difference difference between between measured measured and and perceived perceived light light levels. levels.
AA lamp lamp that that is is dimmed dimmed to to 10% 10% of of its its maximum maximum measured light output is perceived as measured light output is perceived as being being dimmed dimmed to to only only 32%. 32%. Likewise, Likewise, aa lamp lamp dimmed dimmed to to 1% 1% is is perceived perceived to to be be at at 10%. 10%.
Design example
At At full full brightness, brightness, the the measured measured light light in in aa space space is is 60 60 foot-candles. foot-candles. At the lowest dimmed level, 10% perceived light is desired. At the lowest dimmed level, 10% perceived light is desired.
1% 1% measured measured light light (0.6 (0.6 fcd) fcd) is is perceived perceived as as 10% 10% (desired (desired result) result)
5% 5% measured measured light light (3 (3 fcd) fcd) is is perceived perceived as as 22% 22% (2x (2x brighter brighter than than desired) desired)
10% 10% measured measured light light (6 (6 fcd) fcd) is is perceived perceived as as 32% 32% (3x (3x brighter brighter than than desired) desired)
1% 1%Architectural Architecturaldimming dimming 5% High High performance performance dimming 5% dimming 10%Lighting Lighting management management dimming 10% dimming
