[amphead]

Earlier, I created a thread talking about building a blue LED VU meter. The one that I created works wonderfully, with one exception:blue light is a short wavelength. Wavelengths in the ultraviolet and those close to it are blinding! Repeated exposure will blind you! One blue LED of lower output say less than 2000mcd that is diffused is OK for a cool indicator light on your panel, or underneath the tubes on the Millett Max. That is the good news. But do not build a VU Meter with many times that number of blue LEDs that you will be looking at for long periods. That would be akin to looking at the sun from time to time. That would be foolish! I have switched to diffused green LEDs 2000mcd. It looks and performs well. I have also put some translucent white tape, underneath the panel window, which does not show. This makes it bearable and even enjoyable in dim light, without the need to alter my circuit with reduced current flow.

http://texyt.com/bright+blue+leds+an...e+health+risks

 

[amb]

It's a matter of how bright. For panel indicators one shouldn't be using LEDs rated at thousands of mcds, regardless of color. If you do use them, put a high value resistor in series to run them at very low current, so they emit a more reasonable amount of light. Personally, my amps have blue LED indicators, but those LEDs are rated at 40-80mcds, and even then I run them at a much lower current (~1mA) than the indicated maximum.

 

[threepointone]

Usually, LEDs have a relatively tight range of wavelenghts--I'd doubt blue LEDs emit a significant amount of UV. I agree, most of them are pretty darn bright and annoying, but I don't think it has too much to do with wavelength--2000mcd is very intense for any type of LED. It's just that it seems a lot of cheap LED manufacturers these days like to boost their intensity ratings. I read through the articles and the references it gives, and I honestly think the connection between blue light and cancer is at most very tenuous.

Blue LEDs probably should be okay if you decrease the current or better yet find one with a lower mcd rating / larger viewing angle. And another note: the mcd rating is not a measure of how much light the LED puts out, but the intensity.

 

[ericj]

Quote:

Originally Posted by threepointone /img/forum/go_quote.gif And another note: the mcd rating is not a measure of how much light the LED puts out, but the intensity.

Yes, and viewing angle and intensity are inversely proportional. Doubling the angle halves the intensity.

I have some 3mm blue LEDs with a 6 degree viewing angle and 22000mcd rating. At their full 20ma they are eye-stabbingly bright. I typically run them at about 0.7ma.

 

[SilverTrumpet999]

Actually, at the same intensity green wavelengths are perceived far brighter than blue or red. So you would REALLY want to stay away from green - but seriously, you should tone the amperage across those puppies down a bit.

My guess is that you're looking at them in the dark, possibly when tired. At those times I find blue LEDs can be painful to look at as well... Scientific research has found that blue wavelengths have a direct effect on circadian rhythms (hypothesis: blue sky = daylight, unconsciously). Unfortunately I can't find that exact article right now, but it was an interesting read... that much blue light could really mess with your internal clock.

I agree with threepointone, LEDs marketed as blue do not put out much UV (though it should be noted that there have been LEDs manufactured which emit in the UV range, and these would). You shouldn't get a sunburn

 

[amphead]

Quote:

If you do use them, put a high value resistor in series to run them at very low current, so they emit a more reasonable amount of light.

mmmm....hmmm....... agreed! I will be putting them on my Millett Max, just not in my VU meter.
Quote:

I'd doubt blue LEDs emit a significant amount of UV.

Blue LEDs don't emit any UV, they are monochromatic(single wavelength). They do emit a short wavelength, 450-470 nanometers. Thats where the problem lies. Sorry for the rant, I worked as a laser tech.

 

[rockcod]

Quote:

Originally Posted by amphead /img/forum/go_quote.gif mmmm....hmmm....... agreed! I will be putting them on my Millett Max, just not in my VU meter. Blue LEDs don't emit any UV, they are monochromatic(single wavelength). They do emit a short wavelength, 450-470 nanometers. Thats where the problem lies. Sorry for the rant, I worked as a laser tech.

Would you mind elaborate why short wavelength is harmful? I am ignorant.

 

[SilverTrumpet999]

amphead's comment is worded strangely... I believe he meant they emit a short wavelength range. Also, by the technical definition he contradicts himself; monochromatic means there is exactly and only one wavelength emitted. Not even lasers are truly monochromatic (which he should know, having worked as a tech!) - they come close, but have a small range of uncertainty. This may be very small, less even than ±0.1 nm, but no laser is truly monochromatic though they are often considered so because the wavelength range is so small. More expensive lasers often have tighter wavelength ranges.

So because he said blue LEDs are monochromatic, then cited a wavelength range of 20 nm, you are well justified in your confusion. Wavelengths above 400 nm are not harmful in and of themselves, they are in the standard visual range, but (being blue) they may screw with your natural day/night cycle as research has shown. Below 400 nm is the UV range, and those wavelengths can be harmful.

For further reading, peruse the wikipedia article on "Electroluminescence" which is the basic principle of how a LED works. Band-gap transitions cannot produce monochromatic light, though the wavelength range is much tighter than a blackbody-type emitter (such as an incandescent filament) and they require significantly less power.

Now, I apologize for my rant, but perhaps somebody will learn something from this...

 

[franky_s]

Hi everybody,
this is my first post here and I want first say "Hello".
I think SilverTrumpet999 is absolutely right. Just for your amusement I attached two sets of spectral data, one of a blue LED and the other from a green Laser-pointer. I measured theses data myself and I think the data shows exactly what SilverTrumpet999 posted. And please note the different scalings of the x-Axis...

Frank

 

[SilverTrumpet999]

Hi franky_s! Welcome to Head-Fi!

Thanks for the backup/measurements. I am curious; what spectrometer(s) did you use for those? The peak wavelength at ~532 nm implies that the lasing structure was similar to that seen in most green laser pointers, which is by no means a direct method of obtaining the desired wavelength (808nm high-intensity IR diode laser pumping Nd:YVO4 crystal to produce 1064nm photons, which pass through a doubling crystal to yield 532nm output). The extra steps in there are likely the reason why it has almost a 5nm FWHM (Full-Width at Half-Maximum, for the non-physicists)... still way better than a LED, but not quite up to a benchtop model's spectral purity.

Now I'm tempted to grab one of the physics department's HeNe benchtop lasers and hook it up to an optical spectrometer! Wikipedia claims HeNe lasers remain within 0.002nm of the rated 632.8nm output, so that should pretty much return a delta function, but still - my curiosity has been piqued.

 

[threepointone]

I don't remember everything perfectly, as I read up on this about two years ago, but lower UV ranges (UV-B and UV-C, generally < ~300nm) can be absorbed by the the thymine (T) nitrogenous bases in DNA--the UV will turn two consecutive T bases into a thymine dimer. In other words, it'll screw up your genes, which can cause skin cancer. It also messes up a whole bunch of other things in your cells, which is why you can get sunburn. In general, the lower the wavelength, the more your DNA will absorb the UV, and the worse the damage is. Your body has natural DNA repair enzymes which will usually correct minor DNA damage of this type, but prolonged exposure to UV-B or UV-C is not good.

As a side note, this is why the ozone layer is so important; the ozone molecules absorb the bulk of the UV-C and lower wavelenght UV-B from the sun. Without the ozone layer, the UV-C from the sun would be more than enough to really screw up your DNA. UV-C is also what's used to kill bacteria--generally, bacteria have less complex DNA repair mechanisms, and are more susceptible to DNA damage due to UV.

Even most UV LEDs are centered around the very high end of the UV spectrum, about 400nm or so--this is why they're usually still visible as a slightly violet color. This is in the longer-wavelength UV range, which generally does not affect DNA much.


Interesting measurement results--where did you get that blue LED from? I'm just wondering if the cheaper LEDs spew out a less narrow spectrum. The same data is available on LED datasheets, btw.

 

[rockcod]

Thanks all for the clarification -- I love this forum!

 

[amphead]

Quote:

amphead's comment is worded strangely... I believe he meant they emit a short wavelength range. Also, by the technical definition he contradicts himself; monochromatic means there is exactly and only one wavelength emitted.

mmm....hmmm.....You are correct! There is some bandwidth falling on either side of the peak. I should have said peak frequency. You will notice from the graph that a blue led does not come close to straying into the ultraviolet region. What I was attempting to say, was that photons in the blue led spectrum 450-470 nanometers are thrown out in sufficient quantity when used in a large VU meter that they can degrade the rods and cones within the human eye. The short "blue" wavelength means that the photons have more destructive power than longer wavelengths, that other colors possess.

 

[amphead]

You might be confused as to why the long wavelength infrared is also very damaging. This is because human beings are made up of about 70% water. The infrared and even the microwave spectrum excites the H20 molecule. This excitation or heating is destructive.

Many years ago I worked on a machine called a laser scribe, at Intel Corp. This was a YAG laser that produced an infrared/invisible beam. The purpose of the machine was to cut a number into the silicon of a wafer. This was known as the lot number, which kept track of individual chips in the wafer fab, as they were being processed.

 

[amphead]

Just installed blue LEDs in my Millett Max!