Retinal Revolution
April 14, 2009 - 11:00am

Residential Lighting: Explain the new science regarding the human eye.

George C. Brainard:
Light is the primary stimulus to the visual system. That’s been well-studied for hundreds of years. What’s new in the last 25 years is the understanding that light, independently of the visual system, affects human behavior. Those studies, which now amount to a very substantive body of evidence published in biomedical literature, began in the early ’80s and led to many therapeutic applications of lighting. But in the past seven to eight years, there has been a dramatic upheaval in our field: the discovery that the human eye contains two distinct sensory systems.

RL: What is this second sensory system?

The human eye has one system for vision, but a second distinct set of photoreceptor cells affects our biology and behavior. We now know where these cells project to in the brain. We know the photopigmentation in the cells—its amino acid structure and the genes that create it—and that its fingerprint of wavelength sensitivity peaks in the blue part of the spectrum. These cells are not rods and cones. They’re in a different layer of the retina—the ganglion cell layer.

RL: What is this discovery’s significance?

The pigment is called melanopsin. You can take the human melanopsin gene and put it into a non-photosensitive cell and turn

on that cell’s ability to see light. We know that a human kidney cell doesn’t see light, but if you plug in the melanopsin gene, it becomes

photo responsive.

This opens the door for innovation in lighting human environments. Since there’s a second wavelength sensitivity, lighting designs will have to evolve to address traditional values and the value of stimulating the body appropriately for health and well-being. But there’s a lot

of work that has to be done. Since it’s such a new finding, and one not deeply and thoroughly characterized like the visual system, there will be a lot of blind alleys and false leads. It will be decades before we see changes in lighting based on this remarkable discovery.

RL: How will residential lighting be affected?

We’re going to have to learn how to fabricate technologies to a sensory system we didn’t even know existed 10 years ago. All light-emitting sources will change—how they’re placed in environments, what they emit in terms of wavelength and brightness and how they emit light over time. I think daylighting will become a bigger and stronger theme in the future. I also envision indoor lighting that is dynamic to the time of day; the kind of light you need in the morning

is likely to be different from the kind you need in the evening.

RL: Are the forces of change underway?

Internationally, lighting design comes under the purview of the CIE, the Commission Internationale de l’Eclairage. In 2004, the

CIE hosted a special meeting, and it was the first time the standards body invited scientists to explain this new evidence. Two years later, they re-hosted the meeting—a sort of Part 2—and this time invited the contributing bio-logical scientists to meet with the key individuals who

set the standards for both residential and industrial lighting. These are still early days, but it is very emblematic that the CIE would sponsor two meetings to begin laying the ground-work for change.

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