Blue LEDs: A health hazard?

Could a common component used in consumer electronics lead to eyestrain, headaches, disturbed sleep, and even increase the risk of cancer? It sounds alarmist, but in fact the first three of these claims are accepted as fact by experts in relevant fields – the last, the risk of cancer, is unproven.

So what's the deadly component? The blue LED. Yes, those bright blue sparks of light on mobile phones, PCs, toasters, TVs, monitors, air purifiers, medical equipment, electric toothbrushes, and thousands of other products.

Now, don't throw away your electric toothbrush just yet – blue LEDs won't definitely make you ill. But used in the wrong way in poorly-designed products, or used at the wrong time, they can. It may sound unbelievable, but read on.

Nakamura's dream

We see blue LEDs everywhere these days. Product designers tend to use blue LEDs instead of red, green or other colors. There's a reason for that.

Developing the blue LED was very difficult. The first usable blue LEDs were created by Japanese scientist Shuji Nakamura, who followed research leads that others had dismissed as dead ends. Nakamura essentially crafted a new technique for making LEDs, instead of simply extending the processes already used for red and green LEDs. So early blue LEDs required an untried, and very expensive, manufacturing process.

This meant that when they began to appear in products, about seven years ago, they had real kudos. “Every product designer wanted the blue LED,” recalls industrial designer Brandon Eash of Design Continuum, “suddenly there's this brand new color, and it's kind of cool and high-tech looking.”

However, as blue LED makers gained experience, prices fell. An LED arms race resulted. In a battle for consumer attention, product makers adorned their products with more and more of the intense blue highlights.

Consumers get the blues

“From about four years ago, we began to see this gratuitous use of blue LEDs,” said Eash, speaking in a telephone interview from the industrial design house's US headquarters in Boston last year. “Then some complaints from customers started surfacing, saying 'well, these blue LEDs seem very intense'”

An online search will turn up hundreds of complaints from people who are so annoyed by bright LEDs on products that they cover them up or even snip their wires.

“Doesn't matter where you put it, it's like a needle sticking in your eye,” says Steve Nelson, a US-based travel industry worker who was so irritated by a powerful blue LED on a new USB hub that he eventually slapped paint over it one evening. “The damn thing wasn't even right in front of me. So you'd have thought I could just ignore it, but no, even in my peripheral vision it was too bright.”

Are they moaning about nothing?

What's all the fuss about blue LEDs? Surely a light is just a light, no matter what the color. How can there be a difference between blue and red, green, or amber?

In fact, blue light causes greater eyestrain and fatigue than other colors. It is harder for the eye to focus and causes greater glare and dazzle effects. It can also interfere with our internal body clocks, disrupting sleep patterns. Some researchers believe that even very low levels of blue light during sleep might weaken the immune system and have serious negative implications for health.

And because of Nakamura's innovation, blue LEDs really are different from old fashioned LEDs. They are much brighter.

Serendipitous luminance

The process used to make most blue LEDs “lends itself to incorporating quantum wells into the structure”, according to Barney O'Meara, of Canadian LED manufacturer, the Fox Group. “These quantum wells, together with the incorporation of indium in the epitaxy, are features [that help make] high brightness LEDs.”

Whatever the scientific explanation, the effects are obvious. Blue LEDs are literally 20 times brighter than traditional red or green LEDs. Seeing a gap in the marketplace, the Fox Group actually went back to the older LED technology and worked out a new process to manufacture more eye-friendly low intensity blue LEDs.

Other researchers headed in the opposite direction and figured out how to bring the world super-bright red and green LEDs. Despite that, bright blue LEDs continue to cause far more complaints.

Our eyes and our brains have a variety of problems with blue light, but there's no single cause for them. These problems are simply side effects of the ways in which evolution has adapted us to fit the natural environment of our planet.

Blue appears brighter at night

Firstly, blue light appears much brighter to us at night, or indoors where ambient light is low – an effect known as the Purkinje shift. This is because the rods – the sensitive monochromatic rod light detectors which our retinas rely on more at night – are most sensitive to greenish-blue light. (Some hypothesize that animals evolved the rods in underwater and jungle environments, hence the bias to blue or green – later we developed separate full color vision on top of that system, but the sensitive rods remained).

A practical example of the Purkinje Shift: a cool blue power LED on a TV might catch your eye and even attract you to buy it in a well-lit store. But after you take it home, the same LED appears distractingly bright when you watch the TV in a darkened room.

And blue is brighter in peripheral vision

The Purkinje shift also noticeably brightens blue or green lights in our peripheral vision under medium to low light conditions, because there are comparatively more rods towards the edge of the retina – hence complaints that blue LEDs are distracting even when they're not the focus of attention.

“Glaring LEDs on displays that you need to see at night... that's poor design,” says Brandon Eash. Remarkably though, it is a mistake that manufacturers continue to make.

Blue does not help you see clearly

We tend to associate blue with coolness, accuracy and clarity. But paradoxically, our eyes cannot focus blue sharply. We actually see a distracting halo around bright blue lights.

“It's well recognized that blue light is not as sharply focused on the retina as the longer wavelengths. It tends to be focused in front of the retina, so it's a little out of focus,” explains Dr. David Sliney, a US Army expert on the physiological effects of LEDs, lasers, and other bright light sources.

The various wavelengths of light focus differently because they refract at slightly different angles as they pass through the lens of the eye – an effect known as chromatic aberration.

For similar reasons, blue scatters more widely inside the eyeball, says Dr. Sliney, who answered questions by phone last year from his office at the US Army Center for Health Promotion and Preventive Medicine in Maryland

We're half blind in blue

The modern human eye evolved to see fine detail primarily with green or red light. In fact, because we are poor at distinguishing sharp detail in blue, our eyes don't really try. The most sensitive spot on the retina, the fovea centralis, has no blue light-detecting cones. That's right: we're all color blind in the most sensitive part of our eyes.

In addition, the central area of the retina, the macula, actually filters out some blue light in an effort to sharpen our vision. Snipers and marksmen sometimes improve on nature by wearing yellow-tinted 'shooters glasses', which block the distracting blue light.

“You throw away a little bit of color information in order to have a sharper view of things,” explains Dr. Sliney.

Blue glare interferes with vision

The twin effects of fuzzy focus and blue scatter both make intense blue light from a point source, like an LED, spread out across the retina, obscuring a much wider part of our visual field.

Although our retinas simply don't handle blue very well, nobody told the rest of the eye that. If blue is the strongest color available and we want to see fine detail, then we strain our eye muscles and squint trying to pull the blue into shaper focus. Try to do this for too long and you'll probably develop a nauseating headache. This won't happen in a normally lit scene, because the other colors provide the sharp detail we naturally desire.

A dazzling pain in the eye

By the way, the physical pain some people feel from high intensity discharge (HID) car headlights and particularly intense blue LEDs seems to be a combination of these focus and scatter effects, together with a third. We have a particularly strong aversion reaction to bright blue light sources, including bluish-white light. “Pupilary reflex is down in the blue [part of the spectrum]. The strongest signal to the muscles in the iris to close down comes from the blue,” says Dr. Sliney.

Intense blue light can cause long-term photochemical damage to the retina. Now, nobody is claiming that you're likely to suffer this kind of injury from a normal blue LED (unless you stare fixedly at it from a few millimetres for an hour). However, it is theorized that this may be the evolutionary driving force behind the immediate feeling of pain we get from bright light with a very strong blue component.

Our body's instinctive reaction is to reduce blue light entering the eye by closing down the pupil. This means that blue light spoils night vision. After a brief flash of blue, you can't see other colors so well for a while.

Blue light, sleep disorders, and cancer

The chain of cause and effect which might link blue light to serious conditions like cancer is a long one, and far from proven. Blue light's effects on circadian rhythms and sleep, however, are quite firmly established. Putting blue LEDs on a radio alarm clock isn't a great idea.

Light centered in the blue part of the spectrum is known to suppress levels of melatonin in the body. Melatonin, sometimes referred to as the 'sleep' hormone, plays a key role in regulating the sleep cycle.

In summary, when melatonin levels in your body are high, you sleep; when they are low, you wake up. Blue light appears to be a kind of natural alarm clock, which wakes animals as the sky becomes blue after sunrise. Only a fairly narrow band of frequencies centered around 'pure' blue has this strong impact on melatonin.

Even very low levels of blue light, such as are emitted by a single bright blue LED, are enough to suppress melatonin levels. It's perhaps important to understand that the blue light receptors in the retina which affect melatonin levels are independent of our visual system. In other words we don't 'see' with them.

“The air-con unit has a blue power LED. You wouldn't believe how bright it is when the lights are off in the bedroom. I could actually read a book with it,” says Richard, a 30-year-old engineer from Austin, Texas (he asked that his family name not be published).

“I don't know how much the light was stopping me sleeping, but I slowly realized I didn't like it. Maybe I was really sleeping badly [because of the blue LED]. Could be it just bothered me some other way – though I don't think the noise was different than my old air conditioner. But I did feel more tired than usually, had trouble getting awake some mornings. After a week, I slapped duct tape over it [the LED]. I recall my sleeping was back to normal right away.”

While this article focuses on the health effects of blue light during sleeping hours. Pre-bedtime use of some other light sources with a strong blue component, such as high intensity lamps and PC monitors, has also been blamed for causing sleep disturbances, again by stimulating blue light receptors that trigger melatonin production.

The reason that blue LEDs are now seen as a potential hazard to sleep is that they are finding their way into bedrooms, on air ionizers, battery chargers, PC cases and many other popular gadgets. On some poorly designed products they are far brighter than they need to be, and they stay on all the time. Unlike traditional incandescent light sources which emit a broad spectrum with relatively little blue content, blue LEDs put out an intense, single wavelength blue. 

Blue LEDs couldn't really cause cancer? Could they?

Blue light at night reduces our bodies' melatonin levels, which can disturb sleep – this is generally accepted. What is far less certain [PDF] is a link between low levels of melatonin, a weakened immune system, and cancer.

Melatonin has been shown to slow or stop tumor growth in animal and test tube studies. However, in humans, the evidence is much less clear cut. Surveys showing that night shift workers are particularly prone to colo-rectal and breast cancer appear to be the strongest circumstantial evidence [PDF]  for this theory.

According to this line of reasoning, night workers suffer suppression of melatonin because they are often exposed to blue light - from daylight and other sources - during sleeping hours, and low melatonin levels make them more prone to cancer. Of course, one could suggest many other fairly plausible reasons why shift workers might be more prone to cancer, such as bad diet, poor medical care, or stress. However, the animal experiments do seem to add weight to the hypothesis that posits a melatonin-cancer link.

Manufacturers wake up

Following complaints, product designers began to wake up to the user discomfort issues with blue LEDs several years ago. PC peripherals maker Logitech said last year that it was redesigning some products to deal with the problem – although at least one of the company's newer speaker systems still attracts complaints online.

At the lower end of the price scale there's been little change. Less design-conscious manufacturers in developing countries like China appear to be unaware that users might have a problem with all those lovely cheap blue LEDs. Products like PC cases continue to show up with intense blue spotlights on the front.

“There are a lot of products out there that aren't designed intelligently at all. It strictly comes from the manufacturing floor,” commented industrial designer, Brandon Eash in an interview last year, “I think they'll continue to place LEDs wherever they see fit, without much attention.”

Practical advice

If you're bothered by a bright LED on a product, what can you do? There are several obvious solutions: covering with tape is the most common, and shouldn't affect your warranty.

Some users protect the product case with masking tape and them paint the LED housing with a black marker pen or correction fluid. One or two layers should be enough to reduce brightness considerably. This works best for LEDs which have a transparent plastic housing around or above them. It's more difficult for tiny surface mounted LEDs.

To make the light from an LED a bit less intense, you may be able to roughen the surface of the transparent housing with fine sandpaper. Unlike incandescent lights, LEDs project almost all of their light output forward, so diffusing the light helps if the LED is right in front of your eyes.

For recessed or internal LEDs it may be necessary to remove the product's case to access the whole LED housing. If you're going to that extreme, disconnecting the LED or connecting a resistor in series with it is a possibility.

This kind of end-user enhancement will certainly void your warranty, unfortunately, and could be dangerous with high voltage products. Opening power supplies is unwise unless you genuinely know what you are doing.

The long term solution for those who don't like excessively bright LEDs, according to professional designer, Eash: “You should go with another brand. Make the designers pay for their poor design decision.”