Pretty much since the inception of artificial light, people have been using and experimenting with it to alter settings and set ambience, to provide calm, to stimulate. Even if illumination has been the main stock and trade of the lighting industry, human effects have always been somewhere in the mix.

As Bob Karlicek, the director of Rensselaer Polytechnic Institute’s Center for Lighting Enabled Systems and Applications (LESA), noted, “We don’t have the expression ‘mood lighting’ for nothing.”

But in the last few decades, scientists have come to a firmer understanding of how the spectral content and intensity of light can alter biological processes. Many studies have shown a connection, for instance, between blue-rich white light and the suppression of the sleep-promoting hormone melatonin, leading to many warnings about using LED-lit gadgets and computer screens, or even general illumination LEDs, at night.

Conversely, recent research has shown that blue wavelengths can excite a pigment called melanopsin that resides in the eye’s non-visual photoreceptors (known as intrinsically photosensitive retinal ganglion cells or ipRGCs) and sends stimulating signals to the body’s master clock that resides in the brain.

With such impressive science, it seems that lighting is on the cusp of a new human-centric era, in which we can use the same light we use for general illumination to encourage physiological effects such as sleep and stimulation. White light with a strong red spectral makeup might help us sleep. Blue light might help us stay alert and learn. And so on.

What makes the possibility all the more likely is that LEDs lend themselves to delivery of different wavelengths. “The LED allows us to be a little bit more precise than incandescent because you can tune the spectrum,” noted Mariana Figueiro, acting director of Rensselaer’s Lighting Research Center (LRC), a sister research center to Karlicek’s LESA. “You can change the spectrum over the course of the day.”


Nurses Leanne Langhorn (l) and Lone Moeslund (r) pushed for a circadian lighting system at the brain trauma ward at Aarhus University Hospital in Denmark to help patients recover faster. The technology seems to be working, as patients are resting better and are less stressed, among other benefits.

But exactly how the concepts proven in laboratory studies might work across homes, workplaces, offices, factories, hospitals, care homes, schools, and the like is something that is still in its early days and largely unproven on a broad operational level.