2 replies to this topic

[Brian Gray]

I have an LED desk lamp.

I have a solid ebonite pen that has been showing a fade line were the cap lip covers the barrel.

The room has received no sunlight at all. I have blinds covering the windows.

Now of all the ebonites that I use, this one is more prone to fading. I've noticed that. After a pen is manufactured, they are kept in a storage rack that is covered up. I've never seen any fading with this method at all.

But this one pen has been on my desk with the LED lamp on it. That's the only thing that I can figure.

Everything that I read about LED lamps is that they are safe when it comes to skin and UV rays. But is it likely that they are emitting just enough to effect this pen?

Thanks

Brian

Edited by Brian Gray, 28 January 2013 - 02:41 PM.

[FarmBoy]

You should be able to get the lamp emission spectra from the LED manufacturer but figuring out the exact LED you have and the manufacturer can be challenging. In general it will be less than a fluorescent bulb but more directional. You could also find a UV phosphor coated paper and look to see if it is activated under your lamp. I would expect the phosphors used in the white LEDs to have some narrow lines in the UV.

[mhphoto]

Oh goodie! I can use my other hobby-knowledge (flashlight collecting).

Fluorescent lights produce white light by exciting mercury, which gives off light in a narrow spectrum spanning a bit of violet and then up into ultraviolet. This ultraviolet light is then converted by different phosphors that coat the inside of the glass. The quality of light output (that is, the CRI, or "color rendering index", a 0-100 scale measuring how accurately colors are reproduced by a given light) is largely dependent on how many different phosphors are used to convert the UV light. Cheap-o fluorescence usually use 3 phosphors (that convert the UV to the three base colors with some UV left over), but more expensive ones (and I would argue most midrange ones nowadays) have 5 or more phosphors:





But even with all the extra spectrum "spikes" creating a more even white light, our brains know the difference. That's why even the best fluorescents one the market that mimic the color temp of incandescence can't render colors as accurately as incandescents (which have a CRI of 100) and often still look "harsh" to us. We've spent eons with the sun lighting our way (also with a CRI of 100).

I mention all the CFL business because LEDs are very similar.

Most white LEDs start life out as a blue or violet LED. Phosphors are then added onto the chip that strategically convert the higher wavelength light to other wavelengths. But LEDs tend to create a more even output than CFLs. But since most every consumer LED start out below the ultraviolet spectrum, there's no reason to add an element to the mix that creates UV light. And any UV light produced would likely be very, very tiny compared to total light output.

The short answer is, I doubt the LED lamp is doing the damage. Despite very tight QC, no LED manufacturer can make two LEDs exactly the same (which is why you see different lot numbers that are separated by output at the factory, like Cree C5, S2, S3, etc., in higher end flashlights). But even with minute aberrations from the factory, the LED is still most likely starting its life out as blue or violet, not ultraviolet.

That's much more info than probably needed, but I will say that I agree with FarmBoy. UV detection paper or beads to see if your particular lamp spikes in the UV spectrum.