Joan E. Roberts, Ph.D., a biochemist at Fordham University, speaking at the 2015 Lightfair International conference in New York City, stated: “Lighting is not neutral! It will either have a positive or negative effect on human health.” Her presentation raised awareness in the design community on how correct lighting can be therapeutic and incorrect lighting can be hazardous to human health.


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Roberts’ conclusions on the effects of lighting on humans can be substantiated by several recent studies, including one from the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute called “Light at Night and Measures of Alertness and Performance: Implications for Shift Workers,” which appeared in the journalBiological Research for Nursing.

LRC research measured performance and alertness at night under three different light conditions — red light, bright white light, and dim white light. It is becoming well-known that blue light and bright white light (which contains a high percentage of blue light) at night suppress melatonin, which can create health issues in shift workers such as nursing staff. So, it’s not surprising that melatonin levels in test subjects were not negatively affected by red light.

What was surprising was that test subjects performed faster under red-light conditions than in either bright white light or dim white light, a complete reversal from traditional thought on the light needed for high productivity of workers at nighttime. The implications that nursing staff could be exposed to red light at night without suppressing melatonin and changing the circadian phase and, yet, still perform well is significant.

The LRC also has added a circadian stimulus (CS) calculator to its website that anyone can access via Excel to check the spectral power distribution for different light sources.

Two such comparison examples are the 2700K light-emitting diode (LED) and the 3500-Kelvin fluorescent sources. Even though the LED is described as warm white, it still spikes higher in the short wavelength range than the cooler fluorescent source. The short wave-length range is exactly the bandwidth to avoid in light sources at night. Tools like the CS calculator allow lighting designers to make informed design decisions about lighting patterns throughout the day and night.

Lighting designers can specify products that change the color temperature of the source from cool to warm over the course of a day much like daylight changes from dawn to dusk. However, the effectiveness of electric light in activating circadian rhythms in human beings needs more study.

For now, the design community needs to stay abreast of the ongoing research and make reasonable observations about what may be effective or, perhaps more importantly, what may be harmful.