LED fixtures can be very difficult and confusing to evaluate for brightness levels. The reason for this is that most light meters are designed to handle light with a more uniform light frequency spread; LED lighting’s red, green and blue emitters don’t provide this, and the blue light of an LED fixture actually falls somewhat outside of the frequency range many meters detect. An Internet search on evaluating LED lighting will come up with many discussions, and you don’t have to look far before you read about someone using three different light meters on the same fixture and getting wildly different results.
When I evaluated the Chroma-Q Inspire house lighting fixture, I found that my meter read below spec on light output. However, if I adjusted the light to look as similar in brightness to a tungsten fixture as I could (determining this by my Mark I eyeball), I measured 170 lumens at the center of the Tungsten beam, and 61 lumens at the center of the Inspire fixture’s beam. Yet, I’d have called them pretty close to identical in brightness by simply looking at them. Clearly, my less expensive light meter does not do well with LED lighting.
One runs across similar issues in evaluating a fixture’s color temperature. I’ve bought LED bulbs for home use that were listed as daylight, and when turned on during daytime, were radically bluer than the daylight coming in the windows—closer to an arc-source light temperature of a moving light than daylight. Just because an LED fixture reads as daylight (5,200K) on a light meter doesn’t mean that it will be perceived as daylight by your eyeball.
For more information on this problem, reference Mike Wood’s excellent article on the subject here.
