Apr 20, 2021

Data used to compute light levels must account for real-world conditions

By Willard Warren

The IES is considered “the source” for technical data in the art and science of illumination—necessary to design lighting systems for optimal visual performance and choose the appropriate luminaires that are functionally available, plus the prevailing data on energy codes. However, these data have often been insufficient either due to unknowns, such as glare, or outdated information. Therefore, the IES is changing its Lighting Library to make it more current and practical.

At the same time, as many as 90% of us are working from home, and the real estate industry is reeling because when this pandemic ends many of us will not be returning to our former offices. We will certainly benefit from a reduction in the rental cost of corporate office space as well as the cost and inconvenience of commuting. In addition, if we set up our home offices to include daylight, we can reset our circadian rhythms, refresh the hormone melatonin and the chemical serotonin, and get 15 minutes of sunlight each day for our needed vitamin D.

Furthermore, several companies are developing more sophisticated remote and virtual communication systems to compete with Zoom, allowing us to conference audibly and visually with anyone, anywhere in the world. We also expect that many homes and offices will be served with electricity from renewable sources of energy, while visual contact with the outside world will provide us with the broad spectrum of daylight. As you may recall, “dressgate”—where 57% of viewers said a dress was blue and black, 30% saw it as white and gold, and 11% as blue and brown—proved that color discrimination lies in the eye of the beholder, and daylight helps in color discrimination.

AS OUR HOME AND WORK LIVES EVOLVE, so too does the nature of our energy consumption. Regarding the portion of electrical energy that is consumed by lighting, we reported in the September 2020 “Energy” column that a recent advertisement aimed at reducing lighting load claimed that 40% of the electrical energy in office buildings is consumed by lighting, which is highly exaggerated. More recently, a technical magazine article entitled “Lighting and Control” opened with the sentence: “According to the U.S. Energy Information Administration (EIA), lighting uses 17% of the electricity consumed in today’s typical commercial building.” However, that study was done by the EIA in 2012, before LEDs became our lighting standard.

In 2020, the EIA updated that figure to 10%, and it’s been declining every year. In the 2030s, when the DOE will have accomplished its goal of a majority of buildings reaching Zero Net Energy (ZNE), we’ll be able to eliminate the lighting energy load from the energy code.

Did it ever occur to the code writers that there is no validity to the need for decimal points in a lighting calculation since all the components in the calculation of illumination have a variance of plus or minus—and it’s mostly minus—at least 5%? That is to account for the actual lamp lumen output, not the manufacturers’ posted value; the coefficient of utilization (CU) of how much source light falls on the workplane; the true net area of the space; the reflection factor of the room finishes; and the maintenance factor for the accumulation of dirt and dust in the luminaires.

These factors can add up. Putting a decimal point in a lighting calculation may be good math, but it doesn’t reflect the “softness” in the values for the computation of the illumination level—and that’s without considering the usual voltage drop of up to 10% due to “regulation” as a building’s total electrical load increases as the day goes by.


Willard Warren

Willard Warren

Willard L. Warren, PE, LC, Fellow IES, DSA, is principal of Willard L. Warren... More info »