Do Light Bulbs Flicker?
A flickering light bulb can be a great annoyance. For some people, it can also cause headaches, tired eyes and other health complaints. Do light bulbs flicker? Is it something to worry about? and what can be done to eliminate flicker?
What is Flicker in Light Bulbs?
Technically, any quick, frequent change in light intensity can be referred to as flicker. It is caused when the amount of power being delivered to the bulb varies, either through a voltage change or a fluctuation in voltage in the power line itself. How severe the flicker is depends on a number of factors:
- How quickly and regularly does the voltage change occur?
- How much does the voltage change each time?
- What type of lighting is involved?
- How much does the light level vary with each change?
- How constant is the rest of the light in the area?
In the United States, most lights operate on Alternating Current (AC) operating at 60 Hertz (Hz). What that means is that the power to the light bulb fluctuates at twice that rate, essentially switching on and off at 120 times per second. Since changes in voltage are what causes flickering, it can be seen that all bulbs running on AC electricity can be subject to flicker.
Can This Flicker Be Seen?
The human eye can see lights flashing up to a speed of fifty flashes each second, although a range from 10 to 25 times per second is more readily perceived. Above 50 flashes, the human eye doesn't have time to react to the stimulus from the first flash of light and its subsequent dimming before the next flash arrives. So, at 120 Hz, or 120 flashes per second, the flicker is usually too fast to be seen. It looks as though the light is steady and constant.
However, since the light is actually flashing on and off, it can sometimes be seen if there is something nearby that is moving at the same or a similar speed, something like a fan blade. Since the light is flickering at the same rate the blade is spinning, it might cause a strobe effect which causes the blade to appear to slow down or even stop. This happens because the flickering light is hitting each blade at the same point in its movement each time. While this can be an interesting effect when purposely caused by a strobe light, it can be dangerous in certain situations where the brain perceives that the equipment is stopped, when the reality is that it is moving quite rapidly.
What Causes Visible Flicker in Lights?
As noted, rapid changes in voltage is what causes lights to flicker, so anything that causes the power to fluctuate beyond its normal range can cause visibly flickering lights. A bulb that is loose in its socket or faulty wiring may be to blame. Another high powered electrical device turning on and cause a sudden power fluctuation might also cause a light to flicker visibly.
Do All Types of Lighting Really Flicker?
Although all lights run on AC power are subject to 120 voltage changes per second, not all show a perceivable flicker. Incandescent light bulbs supply light by causing a filament inside the bulb to heat up and glow, producing light. In most incandescent bulbs, from the time the power is shut off until it comes back on again 1/120th of a second later is not long enough to allow the filament to cool enough to cause a change in its glow. So even though the power fluctuates, the temperature of the filament remains constant and so does the light level.
Why Do Fluorescent Lights Cause Headaches?
Interestingly, although the human eye can't actually see the flicker in a fluorescent light, some people can somehow detect the flicker in normal fluorescents and it cause them headaches, tired eyes and general visual discomfort. For some reason, their nervous systems seem to be able to tune in on the higher flicker rate, but only with fluorescent bulbs. Although it still isn't understood, multiple studies have directly tied the effect to these bulbs.
The use of high frequency electronic ballasts in these lights cause the flicker rate to change to 20,000 times per second or higher, and this can result in less eye strain. Also, more available ambient light from other sources can also reduce the effect.
Flicker is generally only a problem in lights that use a magnetic ballast as fluorescent lights do. They operate by causing ultraviolet light to shine against a phosphor coating on the inside of the bulb of which in turn causes visible light to shine. This change in light level is perceivable, at least for some people as mentioned previously. Using the high frequency electronic ballasts takes this flicker well beyond perceivable range.
How Can Flicker Be Reduced
If flickering lights are a problem, take the following steps:
- Replace old bulbs. They flicker more and aren't as bright, so flicker is more noticeable.
- Ensure that all parts and connections function correctly. This is especially true of the ballast.
- Upgrade to high frequency electronic ballasts to move the flicker beyond the range that the human eye can possibly perceive it.
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