Reviews Supplements Essilor April 2014 : Page 1
BLUE LIGHT, AND THE VISION, Figure 1. Electromagnetic spectrum and zoom on visible and blue light By developing an experimental framework to distinguish beneﬁcial blue light rays from harmful ones, Essilor has effectively created a new ﬁeld in photobiology research. he electromagnetic spectrum encompasses every possible wavelengths of radiation in our universe. At one end lie the tight, high-energy gamma rays that are so powerful that exposure to these rays can cause cancer in living creatures; while far away on the opposite end lie the long, low-energy frequencies that cause nothing more harmful than AM radio. Near the center of this vast continuum, sandwiched between ultraviolet and infrared energy, runs a very thin sliver of bandwidth that we see as visible light and colors—also known as optical radiation, which ranges from about 380 nanometers (nm) to 780 nm. (See Figure 1.) Within optical radiation, the colors that are blue and bluish, from violet to turquoise, take up a lot of space, about 380 to 500 nm. They have tighter wavelengths and pack greater energy than greens, reds and yellows. Thus blue light is sometimes referred to as high-energy visible (HEV) light. Blue light tends to occur at higher frequencies outdoors via sunlight and at lower ones indoors, where, until recently, most illumination was provided by incan-descent light sources, which burn at higher red and yellow frequencies than the sun. It is known that prolonged exposure to outdoor radiation (both visible and non-visible light) can result in cumulative damage to eye tissues, both anterior and posterior. Ultraviolet radiations are harmful to the cornea and crystalline lens and are associated with cataract devel-opment. HEV light is a known risk factor for age-related macular degeneration T (AMD). It can induce and accelerate photochemical reactions and cell photo-damage, largely mediated by the accumu-lation of reactive oxygen species in the retina, researchers believe. And yet we also know that exposure to HEV light has a beneﬁcial effect as well. It plays an important role in non-visual functions, such as circadian rhythms involving sleep-wake cycles, as well as cognitive, psychomotor, and hormonal balance. Although they have a great deal in common, these two areas of scien-tiﬁc inquiry—the study of HEV light’s positive effects on the one hand and its negative impact on the other—have up until now operated largely independently of each other. But recently, Essilor’s R&D department, working in conjunction with the Paris Vision Institute, unveiled data that maps out a very precise retinal phototoxic spectrum within HEV radiation. 1 For the ﬁrst time ever, researchers can measure the precise physiological condi-tions of illumination using an in vitro model. This paves the way for a whole new discovery of corrective lenses that ﬁlter out harmful HEV frequencies while allowing beneﬁcial ones, to pass through to the eyes untouched. Blue Light Sources Every light source emits a spectrum that can be expressed as a function of a monochromatic wavelength and shown on a graph. For example, Figure 2 repre-sents the spectra in the visible range of typical sunlight, an incandescent bulb, a ﬂuorescent lamp, a halogen lamp, and a cool white light-emitting diode (LED). Depending on atmospheric conditions, time of day, geography, etc., the blue light portion of sunlight is 25-30% percent. Existing artiﬁcial light sources are based on one of two processes: incandescence or luminescence. In incandescent light sources, that is, incandescent bulbs (of the Thomas Edison variety) and halogen lamps, a ﬁlament is heated and emits a light radiation.