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Light it Up: Why some LED lamps seem brighter than others

Posted: November 15, 2018 by Jim Park

Blue-rich white LED lighting is great for lighting parking lots, but the glare it produces is hard on the eyes and it may be inhibiting sleep. Can we make LED light work for us?

TORONTO, Ont. — We take lighting pretty much for granted in this day and age. With the flip of a switch we can continue daytime activities long after the sun sets. As little as 200 years ago, that option didn’t exist. The first street lamp of any kind was a gas lamp installed in 1817. Electric street lighting wouldn’t come along for another 50 years. Since then, we have migrated from incandescent lights and halogen lights to compact fluorescent and most recently to LEDs, or light-emitting diodes.

LEDs are much more energy-efficient than incandescent lights and they last much longer. Primarily for those two reasons, LEDs will be the light sources of the future, but they are not without their problems.

In 2016, the American Medical Association released Human and Environmental Effects of Light Emitting Diode (LED) Community Lighting, cautioning against excessive exposure to blue-rich white LED light. The report describes several related challenges including the suppression of sleep-inducing melatonin, excessive glare while driving at night, as well as a potentially higher risk for cancer, diabetes and cardiovascular disease.

Its authors laid out specific concerns about white LED street lights in residential areas, compared to the orange-ish light produced by high-pressure sodium lighting. The key difference is the “color temperature” of the light. Sodium lighting has a color temperature of around 2,100 degrees Kelvin (K), which is perceived by human eyes as between the light produced by a candle and a 100-watt incandescent light bulb. Human physiological response to that sort of light is calming and restful.

On the other hand, blue-white LED lighting used in street lights and automotive headlamps can be as high as 5,500 to 6,000 K, which humans perceive as daylight. Sunlight has a color temperature of 4,800 K, while a cloudy sky is 6,000 K and a clear blue sky is 10,000 K. Those numbers do not speak to brightness, but the relative blue content in the light entering the eye.

Our brains get signals from our eyes, which tells us when to be active and when to be sleepy. As you might imagine, being bathed in strong blue-white light is a trigger to be awake and alert. In response, the body suppresses production of a chemical called melatonin, which is responsible for triggering sleep. Normally, the body will naturally produce melatonin from around 9 p.m. until the early morning hours when you wake up. If production of melatonin is suppressed or stopped, you will have trouble falling asleep. That’s not to say the lack of melatonin production acts as a stimulant — it just makes falling asleep difficult.

You can see the positive side of that for drivers working at night, and the downside for those living under streetlights that produce high color-temperature blue-white light.

Customized colors

Engineers who design LEDs can vary the chemical compounds used in the devices to tailor the “color” of the light they produce.

“All of that technology is a function of the phosphor recipe,” said Brad Van Riper, Truck-Lite’s former senior vice-president and chief technology officer, in an interview we did a few months before his untimely passing in May 2018. “One of the reasons that parking lot and street lights use cool LEDs is that you get more lumens per watt. So, it’s more efficient to illuminate large spaces like parking lots to get more light using the cool white technology.”

When it comes to headlights, Van Riper said manufacturers use different LED “recipes” for their products that slightly emphasize different colors in the light spectrum. “Cool white LEDs appear brighter, but we believe that that cooler white isn’t the best solution for on-road applications. We hear testimony from drivers about how they believe their depth perception is improved as a result of the color temperature that we selected for our headlights.”

Van Riper explained his company’s warmer LED headlamps better illuminate red objects like stop signs.

While the “brightness” of the blue-rich white LED headlamps is desired in a headlamp from the user’s perspective, high levels of blue produce an undesirable side effect for other road users: a disabling glare. The U.S. Department of Transportation defines it as “the introduction of stray light into the eye, which reduces the ability to resolve spatial detail. It is an objective impairment in visual performance.”

Who hasn’t had a set of those cool-white LED headlamps shining in the rearview mirrors for miles on end? They are not only annoying, they make it harder see in the dark — especially for older driver whose nighttime vision may be declining with age. The University of Michigan Transportation Research Institute (UMTRI) studied the effects of short-wavelength content (blue-rich white) in headlamps more than a decade ago and came to similar conclusions.

LED impact on drivers

You can understand why people living under LED streetlamps may find them annoying, but what impact does the prevalence of blue-rich white LED light have on drivers? We could find any research on that, but one of the authors of the UMTRI report noted above told Today’s Trucking it’s something that should be looked at.

Drivers are only exposed briefly to oncoming headlight, and while they may work in environments bathed in such light, it’s not shining directly on them. One implication could be the in-cab lighting they are exposed to. Again, there’s no research to draw on here, either. However, since LEDs can be “programmed” to produce different-colored light, LEDs could be used to help drivers stay awake during the night and to help put them into a more restful state as they prepare for sleep at the end of a shift.

Aircraft manufacturers are now using LED cabin lighting in various shade of blue and pink to simulate different times of day to help alleviate passenger jetlag — and to calm and relax passengers.

Optronics, a producer of LEDs, is currently engaged with major truck manufacturers in the design of new variable lighting environments for cabs and sleeping compartments. The lighting scenarios being explored would allow an occupant to self-select a lighting combination that they find comfortable, but would also allow them to select pre-programmed lighting environments based on their activities.

“Lighting is more complex than one might think and people can easily misjudge the type of lighting that might be appropriate for the time of day, or the task at hand,” said Brett Johnson, president and CEO of Optronics International. “Optronics’ solution includes a ‘lighting phase’ approach that follows some of the research done by the airlines and others.”

Operators using Optronics’ system will be able to choose the lighting that most closely approximates the phase of daily activity they are in at that moment. For instance, the “awakening phase” would be red-shifted like a sunrise and might increase in intensity over time. The “alert phase” would be blue-shifted like mid-day sun, while the “resting phase” would again be red-shifted but lessen in intensity over time, like a sunset. A “sleeping phase” would minimize all ambient light but might be motion-activated with automatically dimming convenience lighting that would allow someone to use the restroom and go back to sleep without turning on bright lights that might affect optical receptors and cause wakefulness.

“We’re also working on an aftermarket version that could be installed in existing vehicles. Optronics’ sees that the future of lighting isn’t just about more light or one kind of light, it’s about delivering the right kind of light where and when it’s needed,” Johnson said.

“One thing is for sure. For many working people, the world isn’t going to slow down, so it’s up to science and medicine to help us understand the how to best achieve the healthiest balance between lighting, health and safety.”

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