World Expert Reveals Errors In Assessing LED Light Health Risks

Dr Nisa Khan, a respected international pioneer in LED lighting, has triggered consternation in the scientific community. Herein, she provides further insights as to why LED car headlights are a major risk to public health.

Recent appearances on by the world’s leading expert on LED lighting technology have triggered some blowback due to misunderstandings of the science.

A key to such misunderstands is that few critics have grasped that, somewhat like a laser, the critical point of energy intensity in an LED light (where there is most danger) is at the center of the beam.

Critics of Dr Khan’s health warnings have mistakenly focused their rebuttals referencing the off-center light from an LED and thereafter assuming a homogenous light intensity, forgetting that the on-center beam (more akin to that of a laser) is the very narrow field of maximum intensity, from where potential for serious injury exists.

Replying to commentators at Principia Scientific International (PSI) Dr Khan writes:

“Those who still feel like you need to understand further will have to wait until PSI brings you video lectures from me in the future – for which university credits maybe provided as well. These will be paid content as we must incur a good deal of expenses for generating these and these will provide better education over any university lectures currently available.”

Dr Khan explained that well-meaning colleagues, less knowledgeable of the science, have been putting forth demonstrably erroneous information to play down her warnings.

The false arguments proffered are known common red herrings emanating from professionals that belong to CIE, NHTSA, IES, Optica, IEEE, APS and just about all other academic, scientific, technical, and standard organizations.

Undoubted as a world-leading expert, Dr Khan has frankly no equal when it comes to such pronouncements on the scientific facts. Her cited links are to peer-reviewed, or better than peer-reviewed publications. To the few remaining critics prepared to come forward, Dr Khan responds:

“I have been fighting and winning the scientific arguments by all such organisations for nearly a decade now and I again challenge my critics to attempt to refute the science set out in the hyperlinks.“

Those links are as follows:

Confidently re-asserting her position Dr Khan declared:

“There are no peers for my work on LED and wireless near-field photometry and radiometry), you will note that LEDs, lasers, and flat wireless antennas generate beams with non-uniform power density in space and power density at the center of the radiators, be it optical or RF, is enormously larger than what they are off center. This is the basic characteristic of a laser, LED or directive antenna beam. Halogen, HID, and other lamps do not have these characteristics, even after lenses are used like in headlamps.”

In order to understand why at least a 1000W worth of radiant power is easily absorbed by a typical driver on a daily basis when they encounter cars with LED headlights, Dr Khan explains that to cogently debate her critics must have the background in both technical fields of Electronics and optoelectronics.

Electronics and optoelectronics – to address response time for light generation from LED chip devices. This is typically about microseconds. So, in one second, 1 watt of radiant power generated by an LED chip, aggregates to 1 million watts of radiant power absorbed by our body and eyes depending on how much of this radiant power is incident on our body parts.

Dr Khan explains:

“Power adds in time and space. And we need to do the proper calculus to determine just how much wattage is incident on us when we look at an LED light from typical distances and for how long. But even with crude under-approximation, my number of 1000W is nothing compared to what we are experiencing typically. Note that the speed of light is so fast that we can consider instantaneous eye detection of light coming to our eyes from car headlights.”

She Clarified That, While Lumens Are What We See, The Key Here Is The Radiant Power Expressed In Wattage That Is Absorbed By Our Body Parts, Whether Our Eyes Sense Them Or Not.

Having said that, LEDs generate typically 5 to 7 times more lumens within white light spectrum compared to halogen or incandescent counterparts for each electrical watt used to generate light.

“So, this too is more bothersome for LEDs when even lumen power is considered,” she added.

What is required for better understanding is to recognise that radiant power reaching our eyes are far more in the case of an LED headlamp compared to a halogen or an HID headlamp because of power concentration in space in a high or low beam is FAR more for an LED headlamp.

In essence, this becomes a higher-level mathematical calculation, as Dr Khan explains:

“I can do the calculus to determine how much more it is for an LED headlamp vs. a halogen or HID headlamp. This is where the industry is clueless unfortunately. Further, the measurements everyone is doing are incorrect because they simply don’t have the detectors in the right places and the detectors at distances don’t work well for LEDs as they end up erroneously aggregating the power in space without accounting for the highly non-uniform spatial power density in LED headlights.”

For the case of LEDs, she explains, near field measurement must be done accurately and then these need to be extended to typical distances that exist between our eyes and LED headlights.

Not all the electrical power that goes into an LED or a laser converts to radiant power.

“Typically, the power conversion efficiency is about 20 percent; it can be much higher. But I’ll assume that to be the case for my general goal of underestimation of my nominal number of “at least 1000W”! So if you take the 20 percent conversion efficiency, 10 percent overlap of the radiant power from an LED headlamp over your eye when you look at an LED headlight from 2 meters away within a 30 percent solid angle zone, for a sec – what is the total radiant power your eye absorbed? Given the numbers I provided above, let me just say, “You do the math!””

Finally, Dr Khan asserts that has yet to be proper analysis of how our brains processes intense LED light that is hugely non-uniform in space and time and this is the part that gives many people migraines, epilepsy, temporary blindness and dizziness, and other abnormal feelings.

Does that sound familiar?

“Ask yourself, math or not, better light detection or not, color-temperature or not – do LED headlights bother you more than halogen headlights?”

Behind this is the reason that LED headlight peak luminance is much more than 1 million nits where as a halogen headlight peak luminance is around 40,000 nits!

“I have data on this more than most people do. Like man-made detectors, human eye detectors also vary, and some people’s eyes are simply saturated, and they don’t see light level beyond a certain amount. For them, tolerating LED headlights is much easier. However, my studies show that about 20 percent of the population simply cannot take LED headlights at all; another 50 percent put up with it; and about 30 percent likely aren’t bothered by it much.”

For the actual wattage used in a typical LED headlight, look here:

Mind you, the trucks used more powerful LED lights!

Dr Khan’s Challenge To Her Remaining Critics

“If you disagree with anything I said here and would like to challenge me in public, please do the following:

* Reveal your full name and affiliation.

* Bring yourself and any other expert on the subject to a public debate against me.

* In the public debate, I would like the best Bell Labs optical and RF scientists and engineers present. Further, I would like the best math professors who understand analytic functions and Fourier Transforms and Fourier Optics fully. These need not be anybody I know or have worked with in the past. I’ll ask you what you measure when you measure power from a flat radiative source and what that number means. I’ll ask you what you know about near-field photometry and radiometry. I’ll ask you what you know about visible, invisible, and not-so-visible optical radiation and what determines their visibility function for the human eye. I’ll ask you why a laser produces a pencil beam at the surface as shown in Figure 1 in the article written by Donald Nelson, R. J. Collins, and Wolfgang Kaiser. This article is referenced by the author of this article here. Please come prepared.”

About Dr M. Nisa Khan

M. Nisa Khan is the author of, “Understanding LED Illumination” (CRC Press, 2013) – a widely used university textbook around the world in the field of laser and LED engineering and solid-state lighting. She received the B.A. in physics and mathematics from Macalester College in 1986 and the M.S. and Ph.D. degrees in electrical engineering from the University of Minnesota, Minneapolis, in 1988 and 1992 respectively. During her studies, she worked as a research associate for 9 years at Honeywell Solid State Research Center in Bloomington, Minnesota. After completing her doctorate, she became a member of the technical staff at AT&T Bell Laboratories (now Nokia Bell Labs) in Holmdel, New Jersey, and spent most of her 6 years at the Photonics Research Laboratory at Bell Labs-Crawford Hill conducting pioneering work on 40-Gb/s optoelectronic and integrated photonic devices. Dr. Khan then worked on optical communication subsystems at several other companies, including her own venture-backed companies in New Jersey. In 2006, she started an independent research and engineering company, IEM LED Lighting Technologies, and has since been involved in innovation and technology development for making solid-state lighting more suitable for general lighting. She has written over 40 peer-reviewed research articles in IEEE, OSA, and AIP journals, presented numerous invited and contributed papers at OSA, IEEE, and APS conferences, notable international conferences in Europe and China, and has 10 U.S. granted patents as either first or sole author. Dr. Khan performed many feasibility field studies for LED display and signage industries and wrote over 50 LED column articles from 2007 to 2016 in Signs of the Times magazine, which has been serving the electric sign illumination industry since 1906. Dr. Khan’s original scientific contributions can be found in that highlight her discovery of why semiconductor lasers, LEDs, and RF antennas produce directional beams and she is the first to derive the closed-form, analytic equation for near-field electromagnetic radiation distribution from finite, flat radiation sources. This derivation along with the theory of Fourier Optics prove that LEDs, lasers, and flat RF antennas and their arrays are NOT point radiation sources no matter how far the observer is from a flat radiation source. This discovery is very notable and she explains with her new theory why high- power and high-brightness LED-based lamps – used for example as car headlamps – have tremendous glare that propagate directly into viewers’ eyes when their field of view substantially overlaps with the center optical axes of the headlight beams. Her discoveries have been validated by experiments and finite simulations many times over and stand as the only work that can help the auto headlamp industry upgrade their photometric standards for non-point sources that produce non-uniform luminance and radiance – and adopt appropriate measurement techniques that would disqualify all current LED headlamps for having too great a luminous intensity along the optical axes of both high and low beams. Similarly, her work suggests that current 4G and 5G wireless signals generate dangerous levels of electromagnetic radiation for cell phone users and for residents who live nearby antenna base stations. Source:

Dr Khan’s website address:

Listen To Dr Khan’s Interviews, And Other Topical Science And Technology Stories By Principia Scientific International’s Senior Team, At Tntradio.Live