Which devices emit blue light?

What is blue light? And which devices emit it?

I’m reading up on chronotherapy (using light/dark cues to entrain circadian rhythms). I’ve googled blue light but coming up short on info.

Blue light is just the shorter wavelength or higher energy portion of the light or electromagnetic radiation we can see. We have sensors for red light and green light and blue light, and we sense color because of the balance of signals we get from the three sensors. There is any degree of fineness you like in the wavelength or energy of light, but we only divide it up into three categories with our eyes.

Light in general is about as energetic as electromagnetic radiation can get without breaking the bonds in molecules. When it gets more energetic it can break these bonds and create ions, and we call it ionizing radiation and treat it with a little more caution because it can do things like create cancer. Those kinds of radiation include ultraviolet and x-ray and gamma radiation. Actually, light can do some chemistry, which is how we see it, and how camera film works. But light is pretty safe and doesn’t do much.

Lots of devices emit blue light. There aren’t many categories of devices that always, or never, emit blue light versus red or green. Fluorescent tubes emit blue and red and green, and the choices of the powders on the inside of the tube can change the balance between blue and red and green. Incandescent bulbs emit blue and red and green but they emit more blue when you run them at a higher voltage (which also burns them out sooner) and less blue at lower voltage. LEDs can emit blue (at least since about 25 years ago) or red or green, and have to be made of the right materials for whatever color they’re going to emit.

Any more specific questions?

Thank you very much for the explanation!

I’ve always been sensitive to florescent bulbs. I deal with them at work because they’re up about 12 feet above me in the ceiling and I want to be artificially awake at work. But in my home I can’t stand them, or any high watt bulb for that matter. I like low wattage incandescent.

Am I correct in thinking that florescent bulbs, high watt bulbs, computer devices (phones, laptops, etc.) have me seeing the most blue light typically?

The tv (I have an older one not HD or flat screen) and low watt ambient light doesn’t bother me as much. I love being out in sunlight though.

I’m trying to find the best way to minimize light at night and I’ve noted my computer use to be the biggest culprit.

Another device that emits it is the Labatt production line.

There are also Electroluminescent panels/wires/etc that emit blue light. Some phones used this to backlight keys, in the past when we had keys. My watch uses it as well.

mmmmm… And I suppose, if dosed properly, it can help with sleeping.

Not sure in what sense you are sensitive to fluorescents, but many people find the flickering objectionable. It’s not clear how well we can sense the flickering, but I suspect we do at least sometimes. Also, fluorescents tend to emit light with lots of energy at specific wavelengths, whereas sunlight and incandescents feature more evenly distributed energy over all wavelengths. I think we perceive this effect as a weird rendering of color that may make us uncomfortable.

What do you think?

Robert Goulet.

You might find this to be interesting.

It gradually adjusts the color temperature of your monitor at night. It might take a few days to get used to it, but you can adjust the effect to be milder to help with that.

Napier’s already covered it. But to re-iterate,

incandescent lights put out blue light, as does the sun, but only a tiny portion of the light from either of those is blue – most is in the infrared.

Fluorescent lights put out ultraviolet light, which phosphors inside the tube convert to longer wavelength light. You can probably find a fluorescent tube that is weighted more to the blue, but most people want ones that are shifted more towards being similar to daylight. You might try the Gro-Lamps used for growing plants.

LEDs are available that peak in the blue. In the mid-90s they got a lot more efficient. You can get them from a number of sources (online if nowhere else). As we’ve pointed out on this Board many times, “white” LEDs are almost invariably blue LEDs with a phosphor that shifts much of the light to higher visible wavelengths. But you can get blue LEDs without the phosphors. (You can even get ultraviolet LEDs, for that matter).

There are lots of blue lasers. The standby used to be Helium Cadmium lasers (HeCd). Argon ion lasers have blue lines (the ones used for Laserium and other laser light shows use Argon ion lasers). You can also frequency-tripled Nd:YAG lasers to get blue. Tonic Water was even made to lase in the blue, although no one’s ever published a paper on it. There are also blue diode lasers. This list is by no means exhaustive. But I’m sure this is more trouble than you want to go to.

The easiest way to get blue light is to put a blue color filter over a white light source. You can buy blue cellulose acetate filters in large sizes, or get pierces of cobalt blue glass. The hitch is that you’ll be cutting out a lot of light, and most visible sources don’t have a huge amount of blue. If you want to get brighter, use bluer fluorescents or banks of blue LEDs. We actually have a very white fluorescent lamp that Pepper Mill bought for use in the winter months, when we’re short of daylight, and it’s pretty blue. HJer reasoning isn’t far off the idea of chronotherapy.

There are intense sources of short-wavelength light, such as carbon arcs, high-pressure Xenon and mercury lamps, and the like. I suspect these are more trouble than you want, and more light as well.

I don’t know what it is, but I can’t stand to read a book by that kind of light. Maybe it is the flickering. I find reading very calming, but when I see one of those florescent coil energy efficient things I have an automatic prejudice against that kind of bulb. I just say I’m being energy efficient by using a very low watt incandescent and shutting them off when not in use.

Thanks for the suggestion! I just started reading up on it.

effing blue LEDs. You know, the bright ones on electronic equipment that are supposed to make things look cool. The ones that can light up a bedroom or burn out your retina every time you look at your TV/laptop/portable hard-drive/USB charger.

I have taken to using black duct tape on a number of electronic devices to reduce the emission levels (particularly in my bedroom, where I like it to be dark once the lights go out). And blue is the worst, although I also tape over red and green leds, too. The only thing I don’t mind are low-intensity red LED clock digits.


LED area lighting can have a high proportion of blue light in it. My understanding is that they start with an LED that emits blue light, and then use a blend of phosphors to convert some of this blue light to other wavelengths, but the resulting spectrum still has a preponderance of blue light. Consider for example this PDF data sheet for the Cree CXA2530 LED module.. Check out the emission spectrum on page 7. Every color-temperature version has a big spike in the blue; even if you get the 3000K unit (supposedly comparable to halogen), there’s still a major spike in the blue zone.

The problem is that blue light is particularly good at screwing up our circadian rhythm. The general advice seems to be to get plenty of bright light during your waking hours, and avoid bright lights (particularly blue) for a few hours before going to bed for the night.

How much does it matter? There appears to be some evidence that blind and visually impaired people are less susceptible to some kinds of cancer - the connection being that since their eyes never ever tell their brains “it’s daytime”, their bodies never stop cranking out melatonin (whereas sighted people have a daily/circadian melatonin cycle).

It’s amazing how much light gets through your eyelids, too. Lying in bed at night, if you can see your hand waving in front of your face with your eyes closed, then you may have too much light in the room.

Wait, what?

If tonic water is illuminated with UV light (backlight), it shows a blue fluorescence due to the quinine used to give it its slightly bitter flavour. Wikipedia

It’s true. I’d heard this story for years about the “gin and tonic” laser, but couldn’t find anythimg written about it, even though I performed a very thorough search. Many years later, even with computer databases, I still couldn’t find anything.

I finally did learn where the story came from – Kodak used to have a one-page advertisement in Scientific American every mon th. Every month, it was a different page, which had brief discussions of ongoing research at Kodak. One month in the 1970s they included a small piece about how someone had made tonic water lase.
This was better than the story about the Jello laser, because they ultimately had to mix laser dye into uncolored gelatin to make Jello lase (it had been conjectured that “if you hit anything hard enough, it would lase”, but this effort showed that this wasn’t really true). But people at Kodak had been able to use ordinary, off-the-shelf tonic water and made it lase. But the blurb didn’t give any details.

I finally tracked down and corresponded with the parties responsible. It had, indeed, worked, but only with one brand of tonic water, whose name they wouldn’t confirm (I suspect Schweppes). And they had to let it go “flat” – effervescence isn’t good for lasing. But they were very cagey about it. Despite its being published in Scientific American, even if in an ad, they felt it wasn’t respectable research, and somehow detracted from their professional credentials. Me, I feel just the opposite, and if I did it, I’d be bragging.

Nevertheless, although you’d think this would be an interesting undertaking, no one seems to have followed up on it. There are still, to my knowledge, no papers on making tonic water lase, or even of making quinine solutions lase (which you’d think would have no attached stigma). If nothing else, it’d make an interesting high school physics project, or undergrad experiment.
I researched all this for a column on [I\]Edible Lasers*, and added and expanded on that and updated it for the chapter in my current optics book, How the Laser Got Its Zap, which Oxford put out last year.
(I’ve just submitted a column on Edible Optics, to be published sometime this year)

There are special fluorescent lamps with dedicated power supplies that flicker at a much, much faster rate. I am sure people can’t detect that flickering. These fluorescent lamps are most popular (as far as I know) for “machine vision” systems. These are industrial video camera systems that are built into the various machines used in manufacturing industries. For example, a machine that processes bottles may use such systems to control or verify the labels are being pasted on correctly, or a machine that assembles parts may use such systems to get things lined up before pushing them into place. The much faster flickering lets them do things quickly without the pulsing brightness spoiling the measurements.

I don’t know how curious you are about this or what it would be worth to you to check into this, but if you tried using such a fluorescent lamp you would enjoy a test case where the spectrum (distribution over different wavelengths) was like an ordinary fluorescent and the flickering wasn’t.

Cherenkov radiation.