A New Look at Lighting
by Mike Lu
It is often said that we do not appreciate what we have until it’s gone. The adage seems fitting when it comes to lighting – reliable and pervasive, luminaires once installed are then forgotten for the next 20 years. Lighting is simple and works, most of the time. About the only time lighting enters our mind is when there is a burnt-out or faulty lamp.
The advent of solid-state lighting (SSL) is breathing new life and opportunity into that staid landscape. The initial focus has been the energy-saving potential of light-emitting diodes (LEDs). More recently, the “connected” nature of both lamps and luminaires is allowing a new degree of control over the built environment. It has propelled lighting to the forefront of another revolution known as the Internet of things (IoT).
The Society for Information Display (SID) has long recognized the interest in lighting among its members. Lighting has been a special topic at Display Week for several years running. Moreover, SID entered into a friendship agreement with the Illuminating Engineering Society of North America (IESNA) last year. Very broadly speaking, both display and lighting are about the generation of light and its subsequent manipulation. More specifically, we have seen the LED-powered backlight units for liquid-crystal displays (LCDs) morph into edge-lit flat panels for illumination and organic light-emitting diodes (OLEDs) designed for emissive displays enabling both white and color tunable panels for lighting. While improvements in both LED and OLED performance remain a hotly pursued topic, finding new applications for connected lighting draws ever more companies, large and small, into this renewed enterprise.
This issue highlights another emerging and major trend in lighting research, the impact of lighting on health. Dr. Jennifer Veitch from the National Research Council of Canada has contributed an article for this special topic with an overview of the medical research centered on intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells are a separate class of photoreceptors, different from the retinal rods and cones responsible for vision. Reports of a fifth opsin or photosensitive material in the retina, melanopsin, began to appear as early as 1998.1 Evidence clearly linking this opsin, the ipRGCs, and sleep, as well as potentially other biological regulatory functions with light, began appearing
shortly thereafter in 2002.2 A flurry of activity has ensued as the anatomical and physiological links from the ipRGCs to the super-chiasmatic nuclei were established, and with these discoveries a mechanism for light to regulate the human circadian rhythm, including levels of melatonin.3 Blue light at night has been shown to suppress melatonin secretion, which can lead to sleep disorders, and there are even suggestions in the literature that this may be related to a
higher incidence of breast cancer.4
Reducing the putative hazards posed by blue-light exposure at night or during inappropriate times within an individual’s diurnal cycle was the key motivation behind the work described in the second lighting article, by Professor Jou et al. from the National Tsing Hua University in Taiwan. His group has made candle-like (CCT <2000K) OLEDs with minimal blue spectral content. Unlike typical OLED lighting panels with red, green, and blue emitters, these candle-like OLEDs employ four, five, or even six emitters to best approximate the continuous spectrum of a black-body radiator of low correlated color temperatures.
Dr. Veitch’s article further provides actionable advice – as useful as it is rare from an academician! There are gems for both luminaire manufacturers and ordinary consumers of light – everyone in the civilized word. Much of the research is on-going, but all signs indicate that in the not too
distant future, we will develop a new appreciation for the value of lighting, not because it has stopped working, but rather due to its additional functionalities, which include making us healthier, more energized, and more productive.
1I. Provencio et al., “Melanopsin: An opsin in melanophores, brain, and eye,” Proc. Natl. Acad. Sci. 95, 340–345, (1998).
2M. Barinaga, “News Focus: How the Brain’s Clock Gets Daily Enlightenment,” Science 295, 955–957 (2002); S. Hattar et al., “Melanopsin-containing retinal ganglion cells: architecture, projections, and intrinsic photosensitivity,” Science 295, 1065–1070 (2002); D. M. Berson, F. A. Dunn, and M. Takao, “Phototransduction by retinal ganglion cells that set the circadian clock,” Science 295, 1070–1073 (2002).
3M. S. Rea et al., “A model of phototransiduction by the human circadian system,” Brain Res. Rev. 50, 213–228 (2005) and M. G. Figueira, A. Bierman, and M. S. Rea, “Retinal mechanisms determine the subadditive response to polychromatic light by
the human dircadian system,” Neuroscience Lett. 438, 242–245 (2008).
4R. G. Stevens et al., “Breast cancer and circadian disruption from electric lighting in the modern
world,” CA Cancer J. Clin. 64, 207–218 (2014).