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Illumination Basics are Most Challenging for LED Lighting

LED lamps are poised to be invasive, and take over market share from traditional lighting.



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]

LED lamp successes in the display and signage industries are sometimes viewed as justifications for further (expected) successes in the lighting industry. Besides this extrapolation, an industry-wide push for solid-state, smart-lighting systems, which would be embedded (and interconnected) in Internet-of-things (IoT) technologies aiding the incursion of LED-lighting applications, is virtually unstoppable.

LED lamps are poised to be invasive, and take over market share from traditional lighting.

LED luminaire manufacturers’ marketing efforts function because lighting consumers, meaning virtually all of us, choose lighting products as if they were illuminated objects, and not for the way they illuminate. Add such misjudgments to the inherent subjectivity in how each of us sees things, and it becomes difficult to implement the additional standards needed to establish light-quality metrics for LED lighting — and for consumers to recognize the inadequacies of solid-state lighting.

Recognizing light quality is like recognizing food quality. When fast food was introduced in the U.S., many people enjoyed the convenience and taste, and few then questioned if it was inferior to traditional, slow-cooked food. Close to 30 years passed before food scientists and nutritionists determined that certain fast food was unhealthy and, as a result, slow-cooking has become popular again. The interesting point is that fast-food industry growth may have stalled if experts had sooner known –and broadcast — that fast and altered foods are not as healthy to eat as natural food items.

Over time, education has helped people appreciate good-quality and tasty food, but we also face the challenge of subjective tastes.


Subjective tastes also apply to lighting and, currently, LED-lamped lighting parallels the fast-food phenomenon, meaning, the majority of lamp buyers are unable to distinguish that much solid-state light quality is not as good as that derived from certain traditional lamps.

Compared to fluorescent and other gas-discharge lamps, many of today’s LED lamps show superior color properties. And, because many are dimmable, mercury-free, and have higher luminous efficacy (compared to their gas-discharge lamp counterparts), and have equivalent lumen outputs, people — including many longtime lighting professionals — appear convinced that LEDs are sure winners.

But, there are consequences to such decisions.

Manufactured properly, many LED replacement lamps have better color properties compared to their gas-discharge counterparts (for example, CFL, mercury halide and high-pressure sodium), and they are more easily dimmable. However, despite the pleasing presence of some LED lamps’ light (those that do not exhibit glare), the light distribution is not useful for such applications as street and commercial lighting, which requires large-space illumination. A lamp’s light-distribution properties can’t be determined by seeing them as illuminated objects; the effectiveness needs to be measured, and the resulting data used to create adequate, interval illumination between lamps.

The luminous-intensity distribution (LID) of LED-lamped T8s doesn’t spread as widely as the LID from fluorescent T8s (Fig. 1a and b), which should prompt lighting-industry manufacturers to specify both beam and field angles, as identified in my figures. Otherwise, LED lamps can produce inadequate illumination between lamps, while producing too-intense light beneath the lamps (Fig. 2a and b).

Prior to the introduction of LEDs and lasers, the lighting industry didn’t establish basics that would quantify light quality beyond color properties and total lumen requirements. Incandescent, halogen, and gas-discharge lamp manufacturers didn t experience the unique problems brought on by SSL lamps, because the traditional units provided uniform and omnidirectional light distribution, with comfortable intensity levels over very broad angles.


Inorganic SSL s problems are that they are small, discrete, flat sources that produce glare and undesirable light distributions, which are undesirable for large, human-occupied space. LED glare can be obscured with thick translucent covers, but the LID properties will suffer a condition more imbalanced than what is depicted in Figs. 2 a and b – meaning the illuminance in between lamps will be drastically diminished from levels that are already low.

The lighting industry needs to adopt metrics for light-intensity distribution, and levels that are necessary to produce desirable illumination for large, 3-D space. When such metrics are in place, the SSL industry will succeed with lumen and color specifications, and the shift to smart lighting that offers on/off controllability and dimming, via IoT networks, may make sense.

As with high-echelon food, literature, music and other cultural awareness we have developed over the years, if most of us aren’t aware of what exactly makes them high-rank, we face the danger in replacing them with something worse. For LED lighting, the manufacturers need to determine rules and metrics for high-quality lighting, so as to avoid wasted dollars invested in bad lighting, and, eventually, face a disruptive turnaround, as has happened in the fast-food industry.



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