By: Jonathan Z. Kremer
There are many different types of light bulbs around, and they were all designed with a certain use in mind. What follows is a short description of each major type of bulb commonly found in the home, office and factory, how they work, and their uses.
These are the standard bulbs that most people are familiar with. Incandescent bulbs work by using electricity to heat a tungsten filament in the bulb until it glows. The filament is either in a vacuum or in a mixture of argon/nitrogen gas. Most of the energy consumed by the bulb is given off as heat, causing its Lumens per Watt performance to be low. Because of the filament's high temperature, the tungsten tends to evaporate and collect on the sides of the bulb. The inherent imperfections in the filament causes it to become thinner unevenly. When a bulb is turned on, the sudden surge of energy can cause the thin areas to heat up much faster than the rest of the filament, which in turn causes the filament to break and the bulb to burn out.
Traditional Incandescent Bulbs
Incandescent bulbs produce a steady warm, light that is good for most household applications. A standard incandescent bulb can last for 700-1000 hours, and can be used with a dimmer. Soft white bulbs use a special coating inside the glass bulb to better diffuse the light; but the light color is not changed.
Halogen bulbs are a variation of incandescent bulb technology. These bulbs work by passing electricity
Various types of halogen bulbs
through a tungsten filament, which is enclosed in a tube containing halogen gas. This halogen gas causes a chemical reaction to take place which removes the tungsten from the wall of the glass and deposits it back onto the filament. This extends the life of the bulb. In order for the chemical reaction to take place, the filament needs to be hotter than what is needed for incandescent bulbs. The good news is that a hotter filament produces a brilliant white light and is more efficient (more lumens per watt). The bad news is that a hotter filament means that the tungsten is evaporating that much faster. Therefore a denser, more expensive fill gas (krypton), and a higher pressure, are used to slow down the evaporation. This means that a thicker, but smaller glass bulb (envelope) is needed, which translates to a higher cost. Due to the smaller glass envelope (bulb), the halogen bulb gets much hotter than other bulbs. A 300 watt bulb can reach over 300 degrees C. Therefore attention must be paid to where halogen bulbs are used, so that they don't accidentally come in contact with flammable materials, or burn those passing by.
Care must be taken not to touch the glass part of the bulb with our fingers. The oils from our fingers will weaken the glass and shorten the bulb’s life. Many times this causes the bulb to burst when the filament finally burns out.
To summarize, the halogen has the advantage of being more efficient and having longer life than the incandescent bulb. They are relatively small in size and are dimmable. The disadvantages are that they are more expensive, and burn at a much higher temperature, which could possibly be a fire hazard in certain areas.
These bulbs work by passing a current through a tube filled with argon gas and mercury. This produces ultraviolet radiation that bombards the phosphorous coating causing it to emit light (see: “How Fluorescents Work”). Bulb life is very long - 10,000 to 20,000 hours. Fluorescent bulbs are also very efficient, producing very little heat. A common misconception is that all fluorescent lamps are neutral or cool in color appearance and do not have very good color-rendering ability. This is largely due to the fact that historically the "cool white" fluorescent lamp was the industry standard. It had a very cool color appearance (4200K) and poor CRI rating (62). This is simply no longer the case. Regarding color, a wide variety of fluorescent lamps (T12, T8, T5, etc.), using rare-earth tri-phosphor technology, offer superior color rendition (as high as 95) and a wide range of color temperature choices (from 2700K to 5000K and higher). Fluorescent bulbs are ideal for lighting large areas where little detail work will be done (e.g. basements, storage lockers, etc.). With the new type bulbs, and style of fixtures coming out, fluorescents can be used in most places around the home. Most fluorescent bulb cannot be used with dimmers.
Fluorescent tube bulbs
Compact Florescent (CFL)
PL type bulb (CFL)
Note that fluorescent bulbs need components called ballasts to provide the right amount of voltage. There are primarily two types - magnetic and electronic. Electronic ballasts solve some of the flickering and humming problems associated with magnetic ballast, and are more efficient, but cost more to purchase. Some ballasts need a “starter” to work along with it. Starters are sort of small mechanical timers, needed to cause a stream of electrons to flow across the tube and ionize the mercury vapor.
On tube type fluorescent bulbs, the letter T designates that the bulb is tubular in shape. The number after it expresses the diameter of the bulb in eighths of an inch.
Compact Fluorescent Lamps
Compact Fluorescent Lamps (CFLs) are a modern type of light bulbs, that work like fluorescent bulbs, but in a much smaller package. Similar to regular fluorescent bulbs, they produce little heat and are very efficient. They are available to fit screw type base fittings and pin type (snap-in). Most CFLs either consist of a number of short glass sticks, or two or three small tubular loops. Sometimes, they are enclosed in a glass bowl, made to look similar to a regular incandescent bulb. Most CFLs cannot be used with dimmers. They normally last up to 10,000 hours.
High-Intensity Discharge Lamps
High Pressure Sodium (HPS), Metal Halide, Mercury Vapor and Self-Ballasted Mercury Lamps are all high intensity discharge lamps (HID). With the exception of self-ballasted lamps, auxiliary equipment such as ballasts and starters must be provided for proper starting and operation of each type bulb. Compared to fluorescent and incandescent lamps, HID lamps produce a large quantity of light from a relatively small bulb.
HID lamps produce light by striking an electrical arc across tungsten electrodes housed inside a specially designed inner glass tube. This tube is filled with both gas and metals. The gas aids in the starting of the lamps. Then, the metals produce the light once they are heated to a point of evaporation.
Metal Halide Bulb
Standard high-pressure sodium lamps have the highest efficacy of all HID lamps, but they produce a yellowish light. High-pressure sodium lamps that produce a whiter light are now available, but efficiency is somewhat sacrificed. Metal halide lamps are less efficient but produce a whiter, more natural light. Colored metal halide lamps are also available. HID lamps are typically used not only when energy efficiency and/or long life are desired, but also when high levels of light are required over large areas. Such areas include gymnasiums, large public areas, outdoor activity areas, roadways, pathways, and parking lots. Lately, metal halide is successfully being used in residential environments.
Low-Pressure Sodium Lamps
Low-pressure sodium lamps have the highest efficacy of all commercially available lighting sources. Even though they emit a yellow light, a low-pressure sodium lamp shouldn't be confused with a standard high-pressure sodium lamp. Low-pressure sodium lamps operate much like a fluorescent lamp and require a ballast. There is a brief warm-up period for the lamp to reach full brightness.
With a CRI of 0, low-pressure sodium lamps are used where color rendition is not important but energy efficiency is. They're commonly used for outdoor, roadway, parking lot, and pathway lighting.
Copyright © 2004-2005 Jonathan Z Kremer All rights reserved
Jonathan Kremer has over 25 years experience in the electrical field. For more tips and articles please visit http://www.megavolt.co.il