I'm one of those people who can also see the LED Christmas lights flickering. I was trained as a lookout in the Navy and spent a fair amount of time searching for targets in very dark conditions which requires extensive use of your peripheral vision. I'm also a juggler (used to juggle professionally) and this also trains you to use your peripheral vision.
Color receptors (cones) in your eye are mostly located in the center of your visual field and need a lot of light to distinguish color. Rods are more sensitive to shades of brightness rather than color and are more numerous in your periphery. This is why you can see an object at night in your periphery but it disappears when you look directly at it. https://en.wikipedia.org/wiki/Eye#Rods_and_cones You can test this yourself by looking directly at an LED Christmas light and then looking away. As the LED moves from the center of your vision to the periphery the LED will flicker for a brief instant. Incandescent lights also flicker at 60Hz but due to the thermal mass of the filament it does a better job of integrating the light intensity so the flickering is not as obvious. I can very rarely catch an incandescent bulb flickering. LEDs don't emit light by heating up like an incandescent so they actually turn completely on and off at 60Hz (assuming they are being driven by an AC voltage). LEDs have a safe operating envelope that is a combination of peak current and average temperature. LED brightness is directly proportional to the current. If you run the LED continuously at its peak current rating at room temperature it will overheat and burn out. To get the most light and stay within the max temperature rating you can pulse the LED on and off at its peak current and adjust the duty cycle to stay within the max temperature at the maximum ambient temperature you want it to run at, this is typically how LED dimmers work. You also have to pick a frequency that is high enough that the human eye will not detect the flicker. Most people can't see 60Hz flicker but enough can that monitors started supporting 72Hz as a refresh rate. https://en.wikipedia.org/wiki/Refresh_rate If the LED lights are using 60Hz as the frequency for turning the LED on and off there are going to be people who will see the flicker. Despite the flickering I prefer the LED lights because they run at a lower temperature and use less power. Depending on how the LED light string is wired (series versus parallel) the entire string won't die when LEDs stop working. I spent well over an hour going through an incandescent Christmas light string that didn't work, testing and replacing burned out bulbs. When I was done I plugged it in and it stayed lit for all of two seconds. To fix it I would have to retest every bulb again. Needless to say the light string ended up in the trash. I'm hoping the LED Christmas lights don't suffer the same rate of burn out and a single, or multiple bulb, failure won't result in a dead string. I haven't owned a set long enough yet so the jury is still out. keith -- Keith R. Watson Georgia Institute of Technology IT Support Professional Lead College of Computing [email protected] 801 Atlantic Drive NW (404) 385-7401 Atlanta, GA 30332-0280 _______________________________________________ tech-chat mailing list [email protected] http://lists.linuxmoose.com/mailman/listinfo/tech-chat
