Bulb Ballast Starter Switch Power Supply Flicker Color

Flicker

What is it?

Flicker in fluorescent lighting is varying intensity of light, usually between maximum and about 60% of maximum. Lamps using magnetic ballasts flicker at 120Hz under normal operation, which is too fast for us to see.

Who cares?

Well, even flicker that we can't see can still cause eyestrain, headaches and discomfort.

What causes it?

Flicker in fluorescent lighting can be caused by many things.
One of them is variation in the incoming line voltage, though this causes flicker in an incandescent bulb as well, and the cause is often obvious, such as the use of equipment that draws a lot of power sporadically (think arc welders, arc furnaces, MRIs, and even large capacity photocopiers). This flickering is at a low enough frequency to be visible and consciously annoying.
Other causes involve variation in voltage to the bulb, due to a poorly functioning ballast.

What can be done?

Many lamps now use electronic ballasts that run at frequencies in the tens of thousands of times per second (20,000Hz+). In a study by Lighting Research and Technology, it was found that reports of headaches and eyestrain dropped under 50% using these frequencies.

Some things to keep on top of are changing bulbs at regular intervals so they don't get worn out, and verifying that the ballast is functioning properly. A newer working electronic ballast should produce less audible hum than a magnetic ballast.

Why do lamps flicker at 120Hz when household voltage is 60Hz?

60Hz refers to the complete cycle of voltage, which includes a positive and negative part of equal amplitude. Also, the voltage is at zero twice per cycle, or 120 times per second.

What causes the audible hum in these lamps?

The hum is mostly caused by the transformer in the ballast. As AC flows back and through the coils, it creates a magnetic field that interacts with the other parts of the circuit, setting up a 60Hz vibration. Another small factor is caused by magnetostriction, which is when ferromagnetic materials expand and contracts in response to magnetic fields.