Many times throughout my career, I’ve heard stories of renovations that didn’t meet the expectations of the architect, designer or owner because the new lighting was inadequate, mostly due to light levels that were lower than promised or anticipated. It’s a frustrating experience for everyone involved. After all, how could new lighting be inadequate? It usually comes to this: the conditions of the space weren’t properly documented beforehand, so every step that came after was based on inaccurate assumptions.
So, how is this remedied so that anticipation doesn’t turn into disappointment? Here are three steps a lighting designer will take to ensure a better lighting renovation:
1. Don’t Guess in the Dark
In fact, there shouldn’t be any guesswork. It’s always a good idea to be knowledgeable about the existing light sources AND light levels. Whether designing to maintain the current light levels, or increasing them, knowing the current footcandle levels is crucial and a good starting point to any lighting retrofit.
2. 80/50/20—A Good Rule to Break
All too often, these type projects are initiated with only room measurements and replacement fixture selections. Calculations are quickly performed using the default reflectance values of the lighting software and inaccurate light loss factors. 80/50/20 cannot be used for every application. What is 80/50/20? These are the default reflectance values incorporated into most lighting calculation software programs. The software assumes that the finishes selected for the ceiling, walls and floor will have light reflectance values of 80%, 50% and 20% respectively. This is a faulty assumption and should almost always be modified since white ceilings and white walls are no longer commonplace.
3. Light Loss Factor (LLF) – What happened to the light?
Most fixture manufacturers run photometric tests on the luminaires they introduce to the market. These photometric tests are then used for reports and specification sheets, and for producing IES files used for evaluating the performance in lighting calculations. The light output of the luminaire is measured in “initial lumens”. Initial lumens represent 100% light output of a new luminaire. There are a number of environmental influences that will affect the light output of a luminaire (dirt, temperature, etc.), and over the life of the installation, initial lumens will diminish. These conditions need to be applied to the initial lumen output to simulate the expected loss of light.
The first calculation of a renovation or retrofit project should be an effort to recreate the original conditions. This is accomplished by modifying reflectance values to match the space and by making adjustments to the light loss factor until the model calculations are in line with the footcandle readings recorded at the site. The lighting designer will now apply the percentage adjustments to the new luminaire with considerations for the physical properties of the source.
When using Google Maps to reach a destination, one needs to know where they are to get where they are going. Likewise, to achieve a good lighting renovation (destination), the lighting designer (1) must first know where he is by visually inspecting the site and recording the current light level readings and fixture locations, (2) know the actual finishes so that the true reflectance values can be considered, and (3) factor in environmental conditions that affect light output. By taking these three steps, the designer can now proceed with confidence that the lighting design will reflect expectations and receive approval.
Danny Streit is an independent lighting designer, lighting educator and advocate, residing in Nashville, TN. As design principal of DHS Lighting Design, he is Lighting Certified (LC) through NCQLP, is an Associate Member IALD, Member AIA, USGBC, and past President of IES Nashville. You may reach him directly at firstname.lastname@example.org
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