It’s the Blue light emitted by white LEDs that can be dangerous -
Among the most popular household LEDs are products that employ a chip emitting blue light, which is surrounded by a yellow phosphor coating. Although the resulting light looks white to the naked eye, it can feature a spike in the blue end of the spectrum, at wavelengths of 460–500 nm. Light of this wavelength has been shown to have unique physiological effects.
In tests on albino rats, their eyes were actually damaged by thes LED lights:
… the retinas of rats exposed to either blue or cool white LED light showed evidence of retinal damage and cell death after 9 days of exposure. Although rats exposed to cool or warm white CFL lights also showed some evidence of damage relative to unexposed controls, in general differences were much less pronounced than those observed in the LED-exposed rats. The authors suggest the observed injuries may have been a consequence of oxidative stress from reactive oxygen species that were generated in retinal tissue.
For quite a while had nuisance to at times really annoying interference on 80/40/30M. Seemed to vary at lot from day to day.
Of course did all the usual things with computers, wall warts and all the rest.
Noticed a certain individual in a house behind mine whom did not have an enviable reputation around here recently moved out.
Since then the interference has disappeared, which makes me wonder.
I have to say that this has some of the hallmarks of pseudoscience. Light in the 460-500 nm band is abundantly present in sunlight, and the midday sun beloved of mad dogs and Englishmen is much more powerful than artificial light. Albino rats already have pigments missing from their eyes, and I suspect that these already pre-biassed tests were further biassed by overexposure, much as testing for cancer inducing chemicals and foods is biassed by feeding improbably large doses to the test animal. I think that in these days of excessive caution these white LED lamps would already have been banned if there was any likelihood of damage from them, if only to avoid any chance of litigation.
Well it could be a falasy, but like most things, Joe Public goes by what he reads in the Internet or in News Papers and there’s lots of stories about bad light from LED “blue” lights. Anything that stops the spread of Interferance creating LED systems is OK with me! Please note I said “systems” as the RF interferance comes from the power supplies, not the lights themselves.
We use big arrays of purple LEDs at work for photolithography. The purple LEDs (the sort boy racers like to put under their cars) and even the blue ones, typically have useful output into the UV. It’s easier to use a vast array of these than fluorescent tubes when you want good collimation, and they are very cheap. My colleague used, I think, about 4000 LEDs for a 1.5m x 1.5m exposure unit. Fortunately he had somebody else to do the soldering!
Head for the outdoors is probably the best advice.
You can build low frequency 50 kHz switching mode power supply for the 5 V USB using good RF techniques with toroidal coil, filtering capacitors and ground plane. That can pollute your feeding 12V DC power supply though but at this frequency it is usually harmless for the shortwaves.
