Because physics. If the wavelength is longer than the purple end of the spectrum, there is, literally, no way that it can "nuke" you. Only when you get into the UV range that the photons have enough energy to move around links in the DNA. So UV, x-rays, gammas, bad. Yellow, infra-red, radio waves, zero effect. WiFi is radio.
1/24/14 at 3:44pm