What’s in a lux?
Singapore, 16th February 2011
One of the great debates is what really lux levels mean, besides being a unit of light. Many engineers drive their design based on lux levels without really understanding what a lux value means (at least that is my opinion). As far as I am concerned most of the time it means nothing. A lux measurement is only telling you approximately the amount of light falling on a surface, but not what you really see! We basically see reflections, light reflected of materials, colours, etc.!
Today I dived into one of our hotel operator guidelines to make sure our lighting design complies with their standards only to find out that just indicating a lux level and watts per square meter for a certain space does not give explicit directions. It is one of my bones of contention with many operators and it is likely that these guidelines were put together by an engineer and not a lighting designer. Why do I say that?
First where do I measure or need these levels? As an overall space average or localised at specific task areas for reading or working? What about the balance of light in the room. Lighting is about balance of brightness. Another question which is not specified in most manuals is how do I measure the lighting levels? As a standard horizontal level or on a surface perpendicular to incoming light? At ground level or on a working plane level? Without a proper guide on how to measure lighting levels a lux level requirement is hard to verify.
The values also do need to consider the interior design when we talk about interior lighting levels. When 100 lux falls on a black surface the visual impression is totally different then when it falls on a white surface. Obviously the latter one appears much brighter. Yet the lux levels are the same. And I haven’t spoken yet about light distribution… I will do that in another blog :). My point is we don’t design for lux meters, but for people!
In relation to the above I wish to highlight in Light Watch today the technological advancement that LED has seen over the last few years. Same brightness can now been achieved with about 1/5 of the energy. A incandescent candle lamp can now be replaced by a 3W LED equivalent!
Light Watch 33: The LED evolution!