Most LED lights, unless uniquely designed, have “invisible” flicker, typically 60 impulses per second, which the human eye cannot see. But, this can be picked up when you use a mirrorless, DSLR, or phone camera for recording, especially slow motion recording. The “invisible” flicker of LED lights is due to frequency of electricity (60 Hz), which means that it switches on and off 60 times per second (in the U.S. and Canada) and the fact that the diodes of LED lights cool off very quickly, following the electrical impulses (which heat them up). For this reason, LED lighting may not be the best for photography. On the other hand, Metal Halide and Tungsten lights tend to burn very hot and take a long time to cool between electrical impulses, and therefore while they also invisibly flicker, their flicker is undetectable to a camera, even in slow motion.
Note: Invisible flicker is not to be confused with visible flicker. If you can see flicker with your naked eye (where it is blinking on and off) then the bulb is probably failing or there is a defect or interruption in your power supply. At Norb, when we receive returns for bulbs that visibly flicker, about 95 % of them test out ok. As much as we’d like to think that our power supply in North America is perfect, it has imperfections that sometimes show up with LED technology.