Fluorescent light bulbs are lamps that use the phenomena of fluorescence to produce light. Fluorescence is the emission of radiation by a substance that is exposed to an external source of radiation. They are much more efficient than traditional incandescent bulbs, since incandescent bulbs waste most of their energy producing heat rather than light.
Fluorescent bulbs consist of glass tubes filled with low pressure mercury-argon vapor. The inner wall of the tube is coated with a white phosphor. A heated filament emits electrons into the vapor, causing the vapor atoms to emit ultraviolet light. This ultraviolet light is then absorbed by the white phosphor and re-emitted as visible light.
While running, fluorescent lights send pulses of electricity (electrons) through the tube to cause this effect. As a result, the light emitted by these lights also pulses. However, most people can not detect the pulsing under normal conditions, because they take place so rapidly that the light emissions appear constant. Although the pulse rates vary depending on the kind of florescent light bulb, they generally run at a rate of about 120 cycles per second (120 Hz).
- A problem common to many is that compact fluorescent lights (CFLs) are designed to have the tube on top, and the compact ballast below. So, they are designed such that in upright sockets, this is the case. However, when sockets are sidways, they tend to to function for as long before failing, presumably due to overheating. This problem is much worse with inverted sockets. When a CFL light is installed in one of these, the tube ends up on the bottom and the ballast on top. Heat from the tube rises directly into the ballast, and tends to build up there, having few ways to escape.
- Since the pule rate (about 120Hz) is well above the speed that the human eye can seem to generally detect (50-60Hz), it seems that there should be no problem with the use of these. However, there have been notable increases in reports of headaches, eye strain, dizziness, and general eye discomfort in some places when fluorescent lights are installed. High frequency electronic ballasts (which run at a rate of at least 20,000 Hz) seem to significantly reduce these problems, (by up to 50%) but not eliminate them.
However, some counter these statistics by saying that the pulse rate is simply to great to be noticed. They say hypothesize that these problems could be caused by radio frequency radiation (or Radio Frequency Interference/RFI) generated by the ballasts.
- It has been noted that as fluorescent lights age, they tend to produce modulating light emissions. For example, the U.S. National Library of Medicine did a survey of their own fluorescent lights, and found that 42% of their lights were modulating brightness up to 20% and occasionally even 30%. In other words, 42% of their lights were fluctuating their brilliance by about 20%. These fluctuations are noticeable, and can be especially problematic for people with epilepsy, although they may also cause the headaches, and eye strain others sometimes notice as well.
- Fluorescent lighting, headaches and eye-strain. A. J. Wilkins, I. Nimmo-Smith, I., A. Slater & L. Bedocs. Lighting Research and Technology, 1989. Vol. 21, 11-18