As president of IEM LED Lighting Technologies, Dr. M. Nisa Khan consults in the solid-state lighting industry and educates consumers about LED lighting. She has a bachelor’s degree in physics and mathematics, and master’s and Ph.D. degrees in electrical engineering. Email her at [email protected]
Overwhelmingly, Lightfair 2014 — celebrating its 25th anniversary — was all about LEDs, albeit with a few exceptions. This year, the show also officially included electronic signage, which of course, primarily uses LEDs. The show and largest-ever Las Vegas venue attracted more attendees and exhibitors who, once again, overpoweringly displayed LED lamps for lighting.
Just as last year, many lighting and LED firms audaciously said, for all lighting applications, LEDs are today’s choice, moreso in the future. One established lighting company disclosed that LED lighting comprises 30% of its current revenue, and even more of its future revenue will come from LED lighting. In some form, Osram Sylvania, GE, Acuity, Cooper and other firms echoed this message. I was surprised at such boldness because, more than ever, the lighting industry sees tenacious challenges for LED-based lamps and luminaires.
Persistent but subtle challenges
Although LED lamps’ efficacy and color-rendering index (CRI) records are regularly and heroically broken in the laboratory, and many commercial LED modules routinely yield 150 lumen/watts, with a CRI superior to fluorescent and other gas-discharge lamps, certain challenges still aren’t resolved; the blue-light hazard, pronounced glare and non-ideal, spatial-light distribution, for example.
Other concerns comprise non-ideal dimming; flicker idiosyncrasies in discrete, LED-modules’ time-dependent, electronic controls; and stroboscopic effects and striation shadows.
Similarly, but more exaggerated than with fluorescent lamps, LED-caused striation shadows and pulsing can cause certain people to suffer nausea, or seizure-induced dot patterns.
These important LED light-quality concerns appear to be overlooked by light-industry professionals, those who prefer to headline LED efficacy and CRI improvements, as well as their cost reduction.
Of course, such concerns are elusive because the average person doesn’t immediately recognize non-ideal, light-distribution effects, or how subtle disturbances arising from non-gradual spatial and temporal-light variations affect their vision. The reaction comes from our photobiological responses, which relate to evolutionary conditioning by sunlight, fire and, later, incandescent lamps. The latter are ideal light sources because they emit light in a gradual and natural manner over space, time and the color spectrum.
We enjoy sunlight and artificial light that mimics daylight.
For example, incandescent lamps produce natural-light color, intensity levels and spatial distribution, as well as variation in time. Our eyes see color affected by both intensity levels and light distribution and, therefore, such interdependencies create non-linear relationships among color, light intensity and distributions. Essentially, this complicates our static as well as time-dependent visual responses and physiological processes throughout the day. It even affects our nighttime sleeping patterns.
Current LED light characteristics differ significantly from other, more ideal light sources in terms of color, luminance and light distribution in space and time. Although not seen at a first glance, such undesirable traits can become evident over time. Many people who have switched to LED lamps go back to traditional lamps.
Increasingly, LED and lighting designers recognize LEDs’ glare problem, but they’re not clear on the cause. Further, the industry remains ineffective in handling glare because no clear definition of glare exists.
Without such a definition, a glare reduction or elimination solution can’t occur.
The lack of a glare standard, or the ineffectiveness of any existing standard, is exemplified by the LED-lamped and infuriatingly bright automobile brake lights that exhibit excessive glare.
Despite the awareness, to date, no country has published adequate or mandatory glare-limiting specifications, although the Europeans have established a Unified Glare Rating (UGR), EN 12464-1 standard.
Measuring LED luminaire glare is challenging because typical LED lamps comprise many small, discrete and unshielded modules. Further, the UGR definition was adopted for halogen, fluorescent and other gas-discharge lamps primarily, which makes it ineffective for most LED luminaires.
Awareness is key
While LED issues are worrisome, certain steps can sufficiently reduce or eliminate the blue-light hazard and stroboscopic effects. More serious is the fundamental glare issue.
Steve Zimmerman, Greenlight Ventures’ (Carmel, FL) CEO, said glare is his first concern for LED lamps and luminaires. Greenlight makes LED luminaires and other products. I discussed LEDs with him at Lightfair. Comparatively, he said, LED luminaires are not superior to metal-halide or HID lamps for illuminating large, volumetric space.
Steve was surprised that I agreed with his LED vs. HID/metal-halide comparison.
We also agreed that LED lamps, to match pre-determined, luminous flux levels at various areas within a desired illuminated space, must emit enormous amounts of light along the normal (center-orthogonal) axis, which inevitably creates annoying glare beneath the lamps.
Martin Klassen, founder of Klaasen Lighting Design (Perth, Australia) also expressed concerns about LED lighting and glare. His Lightfair program — “Have LEDs High-jacked the Lighting Design Industry?” — specified valid LED objections, but he also described a positive LED future. His present glare-reduction solution, shown via photographs, simply included dimming the lamps.
I agree with Martin. LEDs have highjacked the lighting-design industry. It has occurred because LEDs, an unconventional, high-tech light source, dropped upon an unprepared lighting industry. LEDs are a disruptive technology. They have opened a Pandora’s box.
However, this new, far-reaching technology isn’t yet complete. It demands a deeper understanding of photometric parameters — and the definitions that link to light quality.
Cooperation between multiple-discipline experts — scientists, engineers, designers, manufacturers and lighting designers — can resolve the problems.
Where LEDs makes sense
At Lightfair, Bright View Technologies (Morrisville, NC) displayed attractive, lighting sconces that feature that firm’s patented, glare-reducing film covers. Similar to channel-letter face covers, the sconce covers stand in front of LED arrays that distribute light in attractive patterns. (Fig. 1)
LED challenges are solvable
In truth, glare is strong light concentration caused by a thin and flat light-emitting area. Inorganic LED chips — the basic, light-emitting source elements — are very thin and flat. They comprise very-high-density, light-emitting micro particles that produce light radiation described as Lambertian distribution.
Solving the glare issue will cure striations shadows and, to a degree, color visualization.
Commonly, discrete-LED modules, arranged in a 2-D array, produce Lambertian-like light distribution, which then creates abruptly varying illumination (see LED Update, ST June, page 32).
To redistribute the light in a more efficient and gradual manner, an effective LED lamp or luminaire must change the light distribution near the diode chip*.
Solving the glare problem in LED lamps becomes a primary task for the solid-state lighting industry. Without a proper solution, the lighting industry’s bold movement toward LED lighting will eventually falter, due to disturbing the natural, status-quo visualization of humans.
*Understanding LED Illumination, Chapter 6, M. Nisa Khan.
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