Lighting calculations

Singapore, 17th July 2012

We don’t design for lux meters but for people, yet you will be surprised how many ‘engineers’ wish to see lighting level calculations! I am always very wary about this as most of the time people requesting it don’t even know how to read the print outs let alone understand what the lighting calculations mean. Experienced lighting designers can assess the general feel of the lighting looking at the lighting level calculations, but if you have ever asked participants in a lighting training seminar to tell you what lighting level they look at you will know that none of them are able to guess it even close… You will find guesses varying from anywhere between 100 to 1000 lux. And can you see the difference between 200 and 250 lux…the answer is NO!!

Then there is the issue of material finishes. 100 lux on a black surface definitely does not look as bright as on a white surface, why? Because we do not see lux levels we see reflected light. While lumens/m2 (lux) is the amount of light falling on a surface, candela’s/m2 is what we actually see, which considers the reflection properties (read absorption/ diffusion qualities) of the materials light is falling on. A glossy surface reflects light totally different then a matt finished surface. While you can incorporate certain reflection properties into the calculations the appreciation of the end result very much lies with the experience of the designer. The final judgement only possible in a real life light up.

This afternoon I spent time examining the lighting calculations of a proposed outdoor lighting installation. While the proposed generic concept from the landscape consultant looks nice in its proposed renderings, an experienced lighting designer can see the potential problems, and I spotted several. Very spotty results (lighting levels varying from nil to over 400 lux), a potentially glary light fitting installation (beam control and aiming patterns) and “doctored” end results (from the manufacturer) to show nice results on paper. In reality we will have roads (we don’t know the road finishes), walkways and garden paths (no idea about the finishes) and landscape features (just some general info available). Knowing how that will interact with lights takes much more than just reading the lux levels and uniformities from lighting calculations.

Light Watch 3-105: Some images to give you a feel of the rich palette of materials and their lighting properties…

17. July 2012 by Martin Klaasen
Categories: light watch, lighting applications, lighting design, lighting standards | Leave a comment

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