If the light emitted by the LEDs is "really close" to the mercury light, it should be just as carcinogenic. I also seriously doubt that the LEDs are based on s

If the light emitted by the LEDs is "really close" to the mercury light, it should be just as carcinogenic. I also seriously doubt that the LEDs are based on silicon since indirect bandgap semiconductors make horribly inefficient light sources. Also the bandgap of silicon is somewhere in the near infrared. Frequency doubling requires exteremely high intensites that are usually only reached by focussed laser beams. I don't see how one could use it in a LED.