Almost any white LED light you’ve ever seen was an optical ruse.
That white bulb on a Christmas tree? It’s actually a shining blue diode with a touch of glowing yellow on its tip, says Venkat Venkataramanan, a University of Toronto physicist.
“Yellow and blue (are) complementary colours in the light spectrum,” Venkataramanan says. “When you see them together, your eyes trick you into imagining it’s white light.”
But these days, that old trick is far from the only one scientists working with LED lights have up their sleeves. The coming magic centres on manipulating those lights to better your body and mind.
Indeed, the explosion in LED (light-emitting diode) technology over the past decade coincided with new and expanding neurological insights into the ways light affects our mood, our sleep — our physical well-being.
These discoveries have moved the spotlight on LED technologies away from their immense durability and energy advantages.
Scientists are learning how to manipulate LED lights to tune our biological clocks. They’re seeking to use the lights on long-distance flights to combat jet lag, and in schools to help calm children.
The promise the bulbs hold to improve physical and psychological well-being excites LED researchers like Venkataramanan, scientific director at the U of T’s Institute for Optical Sciences.
It didn’t begin well for LEDs in that regard. Many of us were introduced to them that one December back when we first replaced our vibrant — though fickle and dangerously hot — incandescent Christmas tree bulbs with a string of safe but anemic LED lights.
Those sterile, joyless bulbs were based on the high-intensity blue diode that won its three Japanese developers — Isamu Akasaki, Hiroshi Amano and Shuji Nakamura — the Nobel Prize in physics.
But blue, even in a white disguise, is a cold light. It itches at the brain, which has evolved over eons to crave the rich, full-spectrum radiance of the sun.
So the first order of business was to make a sunnier LED light.
This has largely been achieved by combining various photon-shifting phosphors with the standard blue diode and manipulating the gallium nitrate semiconductor at the blue light’s baseto create a wider range of colours.
Tunable diodes that naturally emit the warmer reds and oranges of the spectrum were also introduced into the mix.
Combining all of these advances in multi-diode packages, new-generation “bulbs” have been created to produce a light much more comforting to the eye.
“Now you can put together various different types of LEDs and create an artificial light source that almost resembles sun,” Venkataramanan says.
But it turns out the visual quality of light was only half the story.
Traditionally, it was thought that light entering the eyes hits only two sets of receptors: the familiar rods and cones that discern its intensity and colour respectively.
“But about 10 years back or so they found out that there are also non-visual pathways of light through (the) eyes,” Venkataramanan says.
These non-visual pathways, he says, take in the spectral quality and fluctuations of light as well. But crucially, they also trigger the production of two key hormones that help control the rhythms of the body and brain.
“One (hormone) is melatonin … which sets your circadian rhythm or biorhythm,” Venkataramanan says. While it helps regulate many bodily functions, melatonin is crucial in promoting rest and sleep, he says.
The other light-activated substance is the stress hormone cortisol, which promotes alertness and is critical for daytime performance.
The body’s daily production of these two competing hormones has been tuned by evolution to the natural cycles of the sun.
And because LED lights can so readily change their intensity and spectral quality, they can be used to help reset our sun-tuned biological clocks — clocks that are perpetually disrupted by the artificial lighting, screen time and plane travel of the modern world.
To this end, Venkataramanan is working with the Zhejiang University in China to create LED lighting that can mimic sunlight.
“We have daylight sensors outside, and take that sensor input to tune the spectrum of light” inside, he says. “So exactly the kind of light that you would get outside is what you would get inside. There are a lot of health benefits (to) being in the natural sunlight cycle and darkness cycle as well.”
Venkataramanan works with chemists, engineers, physicists, psychologists and neurologists in his U of T research. His lab also works closely with the burgeoning LED industry, helping to test the spectral range, directionality and power of new lights with an impressive array of sensing instruments.
One, an “integrating sphere” two metres in diameter, gathers the light from devices hung within — electronically analyzing the intensity and colour quality of the beams collected on its white interior surface.
Venkataramanan predicts that all vacuum-based electronic illumination — from long fluorescent office lights to sodium-vapour street lamps — will be switched to “solid state” LED technologies in little more than a decade.
LEDs “are disruptively replacing almost every technology in lighting.”
LEDs lit to last
Current LED lights last an average of 20 times longer than incandescent bulbs.
They also convert about 10 times more electricity into light than the traditional Edison screw-ins — about 55 per cent compared to 5 per cent.
“Saving energy by having high efficiency … is as good as creating new energy,” says Cynthia Goh, director of U of T’s Institute for Optical Sciences.
Four bright ideas for LEDs
• Blast them with blue
Sullen and sleepy, adolescents commonly trudge into morning classes ill prepared to take in their pre-lunch lessons. One solution proposed by some education researchers is to tune school LED lighting towards the cold, blue end of the spectrum. This would give the narcoleptic scholars a jolt of cortisol to boost their attention levels.
• Healing fixtures
Patients need their rest after surgery. Established research has shown well-rested patients heal better and faster, improving outcomes and lowering health care costs. One idea that’s gaining ground in medicine is to place patients exiting the operating room in large-windowed rooms that can bathe them in natural sunlight. But this runs into cost and infrastructure problems in older hospitals. In the meantime, facilities are looking at LED lights tuned to natural solar spectrums to boost healing.
• Jet lag lighting
Travellers taking long flights — especially eastward journeys — can often encounter days of lethargy as their circadian clocks align to new time zones. One way to help mitigate jet lag might be to tune LED lighting in airplane cabins to reflect the sunlight patterns passengers will experience on arrival. This could give them a head start in shifting their biological clocks to those on their adjusted watches and smart phones.
• Nursery good night lights
The lights you turn off when putting your baby down for the evening may be the reason you’ll be up again in the middle of the night. The harsh blue light emitted by many existing fixtures can make it difficult for infants to sleep. Using LED lights that can be tuned to the warmer, reddish end of the spectrum might boost your baby’s melatonin levels, and ensure both infant and parents get a better night’s rest.