Have you ever encountered an alien coming towards you that is nothing more than a giant ball of glare?
The auto industry has been busy replacing halogen headlights with Light Emitting Diodes (LEDs) because the LEDs are small, powerful, and consume little energy. The problem is that the National Highway Traffic Safety Administration (NHTSA) has not understood that LEDs are a directed-beam light, nearly a laser beam. The NHTSA regulations such as FMVSS-108 are not applicable to directed-beam lighting. In addition, the measurement devices that NHTSA uses are not sensitive enough to detect the changes in luminance associated with directed-beam lights.
Without regulation and precise measurement instruments, the LED chip industry and the auto industry have been free to produce and install LEDs without any restrictions on how intense they can be. As of 2018, LED chip makers had reached 100,000,000 nits of peak luminance, whereas human tolerance is 50,000 nits and human comfort level is around 300 nits.
Besides the peak-luminance issue of directed-beam LEDs, another issue is called Spectral Power Distribution, a graph of the energy levels of the light at each frequency in the visible spectrum. LEDs have an unnatural SPD, with a large spike of high-energy blue wavelength light that causes the glare shown in the photo above. Again, NHTSA has no regulations for this Spectral Power Distribution. The industry uses a single value called Correlated Color Temperature instead of SPD, and, although not entirely accurate, does convey the problem. While a halogen headlight may have a CCT of 3,000 Kelvin, with little blue wavelength light, today’s LED headlights have a CCT of 6,500 Kelvin, which signifies a large amount of high energy blue wavelength light that causes glare and eye damage.
Figure 1 – Spectral Power Distribution for 6500K LED 
A third issue is a flicker. Automakers may use Pulse Width Modulation to limit the brightness of the LED lights by turning the current to the chip on and off. This flicker can strongly negatively impact our central nervous system, even if we don’t see it consciously.
There is a misconception that the auto industry is fully aware of these issues, but the truth is that all these issues are being ignored. The auto industry, including NHTSA, the Insurance Institute for Highway Safety (IIHS), and American Automobile Association (AAA), are still acting as if LEDs are just the same as uniform emitters such as halogen. The industry needs to recognize that LEDs are a directed-beam light with non-uniform luminance. Once this is recognized, the industry must develop all new regulations to protect human eyes and limit glare and develop all new measurement devices and software.
What can you do? Many articles will suggest closing one eye or looking to the right. We find these suggestions to be dangerous. Closing one eye reduces your vision by 50 percent. Looking to the right means ignoring what is on the left. What about when drivers are making a right turn from a parking lot onto the street? Are drivers not supposed to look to the left to see if any cars are coming towards them?
The only way to get this solved is to let the authorities know. Make a submission to firstname.lastname@example.org to let the National Transportation Safety Board know whenever you encounter a blinding LED headlight. Feel free to describe your incident and/or provide photos. Also, call your Congressional representative in Washington, DC, and tell them you want NHTSA to regulate “chip-level peak luminance,” “spectral power distribution,” and “flicker.”
Editor’s Note: The opinions expressed in this article are those of the author.
Mark Baker is the founder of SoftLights.org, an international advocacy group dedicated to requiring stationary and mobile lights, including vehicle headlights and flashers, that are human and ecosystem compatible.