096
TECHNOLOGY / LED
ENLIGHTENING LEDS
As an epigenetic design practitioner, my job is similar to most lighting and design professionals except that I also take the position of a scientific researcher striving to understand how the built environment directly affects the human animal. Report- ing on the known physiological, metabolic and neurohormonal consequences of how the spaces we design impact the people who inhabit and experience our designs is a role that is growing exponentially as we go further into the land of LED forecasted dominance. Coinciding with a recent French study documenting the negative impacts upon the retina as a result of exposure to short wavelength light, my intent is to raise awareness to the growing concern for human ocular and overall health impacts arising from the increased use of new light sources for roadway lighting, automotive headlights and pedestrian lighting. I am particularly concerned about the trend to- wards the increased use of short wavelength light in the range of 450-484nm due to the potential for retinal toxic stress and other negative impacts upon the human eye. I believe that the detrimental effect of these new light sources will be most notice- able in older people because their vision is adversely affected due in part to two de- grading anatomical characteristics. The first is a measurable size decrease of the pupil correlated directly with advancing age. This occurs when tissue of the iris swells thus preventing the pupil from adapting by open- ing to its full extent in dim light. In dark- ened conditions, the pupil diameter of a 45 year old is 6.2 mm and decreases to 5.2mm by age 80, while in the light adapted state it is further reduced to 3.4 mm. Coupled with the normal 2mm shift of pupil size which occurs when attention shifts between center and peripheral focus in the presence of bright oncoming light, the older pupil will have dramatically less ability to admit and shield light at night. Because pupil dilation is influenced by the circadian clock targeted iPRGC response, an increased expression of a stress related neurotrans- mitter known to control pupil activity can also be expected as the percentage of short wavelength light at night increases. The aging process also affects ocular health by increasing the amount of glare expe-
The IALD Enlighten Americas conference, held in Denver earlier this year, included some thought-provoking seminars. Among them was a joint talk by Jim Benya and Deborah Burnett. Here Deborah gives the epigeneticist’s view on the widespread adoption of LED
rienced in the presence of bright light. Recognized as a sensation of blinding white- ness, blackness and/or physical irritation, glare is actually a metabolic failure of the retinal surface to quickly remove cellular waste in response to changing light condi- tions. When light strikes a photoreceptor the retinal cell generates a unit of work which produces a waste by¬product that dissipates swiftly in the younger eye. As the eye ages, the rate of removal slows and the waste by-products build up thus causing the temporary “blinding” effect we identify as glare. Since short wavelength light peaks strike the retina closer together, it causes the cellular “work load ” to occur up to 2 trillion times faster than longer wavelengths thus causing the cellular waste to build up faster than can be processed. This in turn exacerbates the disability sensation of glare in a manner that will increase with age. Short wavelength light also plays a nega- tive role in the metabolic process called the ‘visual cycle’. Normally when light hits a photoreceptor the photon is absorbed by a receptor which immediately converts or transduces the stimuli into an electrical signal. This metabolic process ‘bleaches’ the photoreceptor rendering it useless until a specific period of time has elapsed. The recovery time is needed for the regenera- tion of the photopigments to regain full
sensitivity. In the presence of bright blue rich light, current scientific opinion is that this process is reversed and the cell becomes receptive again before it has had time to fully recover, thus possibly leading to retinal distress. In summary, several negative impacts to human ocular health are exacerbated by bright light at night. With the historic bal- ance of most outdoor lighting being the long wavelength light of high pressure sodium lamps, the short-wavelength dominated LED light sources will tend to create more glare and acuity issues with night vision. This has already been noted and readily apparent to most drivers since the introduction of xenon HID headlights. And with short wavelength LED street lighting having many of the same issues, it legitimately raises the question of whether these new light sources are intro- ducing as many problems as those they are claiming to solve.
An extended version of this article is avail- able at
www.mondoarc.com Deborah Burnett is a registered interior designer, licensed general contractor and practicing lighting consultant recently part- nering with James Benya FIES, FIALD in a human-centered consultancy which provides daylighting, lighting and epigenetic design assessments and services for leading A/E and ID firms worldwide.
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