I’ve heard (from observations recorded in an office environment) that fluorescen…

I’ve heard (from observations recorded in an office environment) that fluorescent light bulbs “emit” their energy at a certain frequency. If this frequency is at or below the rate at which our eyes blink/scan, this will cause eye fatigue and other health “problems.” What would be the best light system for the office environment?

Fluorescent light bulbs flicker rapidly because they operate directly from the alternating current in the power line. The light that you see is emitted by a coating of phosphors on the inside surface of the glass tube. These phosphors receive power as ultraviolet light and emit a good fraction of that power as visible light. The ultraviolet light comes from an electric discharge that takes place in the mercury vapor inside the tube. Since this electric discharge only functions while current is passing through the tube, it stops each time the current in the power line reverses. Thus, with each reversal of the power line, the discharge ceases, the ultraviolet light disappears, and the phosphors stop emitting visible light. So the tube flickers on and off. However, the alternating current in the United States reverses 120 times a second in order to complete 60 full cycles each second. The fluorescent lamps flicker 120 times a second. Even the very best computer monitors don’t refresh their images that frequently because our eyes just don’t respond to such rapid fluctuations in light intensity. In short, you can’t see this flicker with your eyes. If you get eye fatigue from fluorescent lamps, it’s the color or intensity of the light that’s bothering you, not the flicker. It’s just too fast to affect you.

Why does a fluorescent bulb sometimes appear blue, especially right before it bu…

Why does a fluorescent bulb sometimes appear blue, especially right before it burns out?

I’m not aware of any tendency to change colors as it begins to burn out, but many fluorescent bulbs are relatively blue in color. The phosphor coatings used to convert the mercury vapor’s ultraviolet emission into visible light don’t create pure white. Instead, they create a mixture of different colors that is a close approximation to white light. There are a number of different phosphor mixtures, each with its own characteristic spectrum of light: cool white, deluxe cool white, warm white, deluxe warm white, and others. The cool white bulbs are most energy efficient but emit relatively bluish light. This light gives the bulbs a cold, medicinal look. The warm white bulbs are less energy efficient, but more pleasant to the eye.

Do fluorescent light fixtures emit magnetic fields? If so, would they be intense…

Do fluorescent light fixtures emit magnetic fields? If so, would they be intense enough to affect diskette magnetic media?

While fluorescent light fixtures do emit magnetic fields, those fields are far too weak to affect magnetic media. Any electric current produces a magnetic field, even the current flowing through the gas inside a fluorescent tube. However, that field is so weak that it would be difficult to detect. Nearby iron or steel could respond to that weak magnetic field and intensify it, but the field would still be only barely noticeable. The only strongly magnetic component in a fluorescent fixture is its ballast coil. The ballast serves to stabilize the electric discharge in the lamp and relies on a magnetic field to store energy. However, the ballast is carefully shielded and most of its magnetic field remains inside it.

As for affecting diskette magnetic media, that’s extraordinarily unlikely. Even if you held a diskette against the ballast, I doubt it would cause any trouble. Modern magnetic recording media have such high coercivities (resistances to magnetization/demagnetizations) that they are only affected by extremely intense fields.

We have some problems with a “fluorescent lamp igniter”, the device that turns…

We have some problems with a “fluorescent lamp igniter”, the device that turns on the lamp. I would like to know what is necessary for the fluorescent lamp to turn on?

A fluorescent lamp produces light as the result of an electric discharge that takes place inside the lamp tube. Electrons, emitted from hot filaments at each end of the tube, are pulled through the tube by electric fields and collide violently with mercury atoms inside the tube. These mercury atoms then emit ultraviolet light, which is converted to the visible light you see by the phosphor coating inside the glass tube.

To emit the electrons needed to sustain the discharge, the filaments at each end of the fluorescent tube must be heated. In the “preheat” style of fluorescent lamp, these filaments are heated red-hot for a few seconds by sending current directly through them. There are two pins at each end of the tube and current is sent to the filament through one pin and extracted through the other pin. Once the filaments are hot enough, the lamp turns off this current flow and tries to send current through the tube itself. If the discharge starts, the discharge is able to keep the filaments hot enough to emit electrons continuously. But if the discharge fails to start, the filaments are heated some more to try to release enough electrons to initiate the discharge.

The “igniter’s” job is to preheat the filaments for a few seconds and then to test the main discharge. If you see no red glow from the filaments at each end of the tube or you see no attempt by the igniter to start the main discharge, then the igniter should be replaced. It could also be that the tube itself is bad—that its filaments have burned out. If you see only one end of the tube glowing red or you see the igniter trying repeatedly to start the discharge, the tube is probably bad. I’d suggest replacing both the igniter and the tube and seeing if that fixes the problem. The only other component of the lamp, other than wiring, is the ballast—the device that controls the amount of current flowing through the discharge. It, too, could be bad.

Do neon lights have glass that is not colored, but has phosphors that emit a par…

Do neon lights have glass that is not colored, but has phosphors that emit a particular color?

A true neon light tube has completely clear (no color, no phosphor) glass surrounding a thin gas of neon atoms. When current runs through that gas, the neon atoms emit red light. In “neon tubes” that emit colors other than red (green, pink, orange, yellow, etc.), there is a layer of phosphor on the inside surface of the glass and mercury vapor inside the tube. These fluorescent tubes probably don’t contain any neon at all. You can see the light coming from the phosphor coating. In a true neon tube, you can see the light coming from the gas itself, well inside the glass tube.

Does the size of the bulb affect its intensity?

Does the size of the bulb affect its intensity?

The intensity of a normal fluorescent light bulb is determined by how many times each second (1) a mercury atom can absorb energy in a collision and emit a photon of ultraviolet light and (2) a phosphor particle can absorb a photon of ultraviolet light and emit a photon of visible light. The first rate depends on how much current and electrical power can flow through the tube, which in turn depends on (A) the geometry of the tube and (B) the density of mercury vapor inside. As for (A), the long, thin tube seems to be the best geometry choice for a low voltage (120V) tube, producing a certain amount of ultraviolet light per cubic centimeter of volume. The longer or fatter the tube, the more electrical power it will require and the more ultraviolet light it will produce. As for (B), at room temperature, the density of mercury vapor is just about right. In very cold weather, the density drops quite low and the bulb becomes dim (thus fluorescents are not recommended for outdoor use in cold climates). Finally, the second rate (conversion to visible light) depends on the coating of phosphors on the inside of the tube. A tube that is too fat will send too much ultraviolet light at the phosphors and they will become inefficient. So a long thin tube is a good choice again. Each region of tube surface converts the light from a relatively small volume of mercury gas. Overall, the intensity of the bulb scales roughly with the volume of the tube. Big tubes emit more light than little tubes. One of the challenges facing fluorescent lamp manufacturers is in making small tubes emit lots of light. To replace an incandescent lamp with a miniaturized fluorescent, that miniaturized fluorescent must emit lots of light for its size. They’re getting better every year, but they aren’t bright enough yet.

What happens when a fluorescent lamp flickers during start-up but doesn’t fully …

What happens when a fluorescent lamp flickers during start-up but doesn’t fully light?

Sustaining the discharge in a gas lamp requires the steady production of charged particles. Even if a lamp contains many negatively charged electrons and positively charged ions, these particles will quickly migrate to the electrodes once electric fields are present in the tube. If they don’t produce more charged particles as they fly across the tube, these charged particles will quickly disappear and the discharge will stop. It takes a critical number of charged particles in the tube to ensure a steady production of new charged particles. Thus the tube may not always start, even if it has a brief flicker of light.