LED Flicker - Learning Objectives
What is causing all this flickering of lights?
Since LED light sources do not mimic daylight, there is a need to have some metrics for comparison to familiar light sources of sunlight, incandescent and halogen.
Flicker is a difficult challenge
Mate your LED with the correct driver and dimmer!
LED's require a driver. A driver is a current controlling device that is similar to a transformer. The driver converts 120 volt power to a lower voltage that is comfortable to the LED light source.
Since LED's are tiny electronic chips, they are very sensitive to changes in electrical current.
If you try to dim an LED light with the wrong kind of dimmer, you may get flicker, or the light will got to zero more quickly than desired.
Manufacturers have been working hard to solve this problem. The solution is to 'mate' the LED + driver + dimmer in a pre-tested configuration that has been tested to provide smooth dimming.
DC power supply may not flicker.
Magnetic dimmers may not cause flicker because they do not 'cut' the shape of the wave of current where you have 'blanks' and 'peaks' in the sine wave curve, that cause flicker.
"Flicker is a rapid variation in light source intensity, usually most noticeable in peripheral vision. Individuals vary widely in flicker sensitivity. Almost all lighting systems produce some flicker, but most people are ale to tolerate minor fluctuations in light output over time. More -severe flicker can contribute to headaches, photosensitivity, epileptic seizures, and other health issues. Even if the flicker cannot be consciously detected by an individual, it may still affect the person neurologically." 
Lighting Facts - Comparing the numbers
DOE - Department of Energy