As a lighting rep, I often get calls about issues in the field. Sometimes light fixtures are not performing as expected once installed and the owner has questions. It could be the fixture is not aimed properly or it was installed wrong. Other times we discover that the lumen output is too low or too high. Typically, these issues can be avoided if we perform photometrics during the design process. However, I have learned that almost every job has at least one hiccup with the lighting. Even if all quality control measures are implemented, a small error in the part number can cause major issues.
What is light distribution?
The distribution of light refers to how the light is dispersed once it exits the fixture. The optics can be at the LED diode level or built into the reflector or housing. If optics are not incorporated into the fixture, then the light is just a “blob” with no real direction or focus. Focusing the light improves efficacy and puts light only where you want it. Lumens do not equal performance. That is why initial lumens are not the same as delivered lumens.
Case study
One such call I received about an issue after installation was at Southwest Adventist University in Keene, TX. A linear wallwash fixture was lighting a 9ft tall painting. The painting had great significance to the university and needed to be highlighted. After the fixture was installed, there was not an even wash of light, only a visible hot spot at the top of the painting. After reviewing the order, I saw the optic was 120 degrees. This wide beam was not tight enough to throw 9ft down the face of the painting. We ordered a more narrow 10 x 30 degree optic and added a louver to shield the light source. This resulted in an even wash of light on the painting without any glare.
In the photo, you can see the hot spot at the top of the painting. In contrast, the new fixture with a more narrow optic eliminates this hot spot and also throws light onto the base of the frame. This light at the base tells you that the fixture is throwing far enough.