Fashions in home lighting have been changing ever since Edison invented the light bulb. One of the latest developments to catch on on it track lighting, a commercial item that's become a part of contemporary room decor.

Track lighting, which generally uses overhead spotlights, is a highly flexible and relatively low-cost way of lighting a room well. In many instances, a moderately handy person can easily install it in place of existing ceiling fixtures. When misused, however, track lighting can be a disaster. And in some cases, it should not be used at all.

"Visual comfort and appearance are the important things," said Alexander Bonvini Jr., president of the New York section of the Illuminating Engineering Society. "People spend a lot of money decorating or furnishing a house or apartment. Why botch it up by adding something alien, which track can be?"

Track lighting does not, for example, usually look good in a highly stylized traditional room, he said, such as one from the Federal period, particularly if the room contains period ceiling decorations.

Bonvini is senior partner in Bonvini-Condos Associates, a Manhattan lighting consultant firm for businesses, industries and, occasionally, wealthy homeowners. Bonvini is neither an advocate nor a critic of track lighting. To him, it's just another tool in his lighting kit.

Deciding whether to use track lighting is a matter of common sense and some basic knowledge, he said. Here are some guidelines, based parimary on Bonvini's advice:

Track is just that, a ceiling or wall mounted track, usually less than 2 inches wide. It comes in a variety of finishes and colors, and is usually screwed into the ceiling (or occasionally, into a wall).

An open, electrified channel runs the length of the track. A variety of swiveling fixtures can be pushed into the channel, secured and pointed in any direction. Adapters are available that allow many types of pendant lamps to be hung from the track. The opportunity to use different kinds of lamps anywhere along the track gives the system its basic flexibility.

Tracks can be either single or multiple-circuit. On a single-circuit track, all the lights go on and off at once. Such single track is available with a long cord that can be plugged into a regular electrical outlet. A multi-circuit track provides for two or more sets of lighting on one track, each controlled by a separate wall switch. And while multi-circuit tracks are more versatile, they are also more expensive and difficult to install.

Track is rated to carry a given amount of wattage, usually 600 for tracks sold to homeowners. Total wattage should not exceed the maximum, although 600 is usually more than enough for the average room. Whatever the stated wattage, keep in mind that the average house circuit can safely supply a total of about 1,200 watts to track lighting. Also consider other appliances on the circuit, such as air conditioners, that might draw enough additional power to blow a fuse when the track is on.

Fixtures attached to the track hold the lamps or bulbs. The most common shapes are cylinders, squares and spheres, in a large array of colors and finishes. Many overhead systems will accept a common light bulb, although a reflector is then needed to push the light in the right direction. However, even with a reflector, a common bulb doesn't provide illumination where it's needed as well as a reflector lamp. The two basic kinds of lamps normally used in a track system are the R-lamp (reflector lamp) and the PAR lamp (for parabolic aluminized reflector). Both produce more light (called lumens) at a given wattage than regular bulbs and place it more precisely. The PAR lamp throws a stronger light -- "the most light for the money," Bonvini said.

Depending on the particular lamp, R and PAR lamps have different beam spreads (the area that the light from the lamp covers), degrees of brilliance and the like, so it's worth combing catalogs and talking to lighting-fixture personnel to find the right ones for a particular need. R and PAR lamps cost more than regular light bulbs, but last longer. While a regular bulb might last 700 hours, Bonvini added, a comparable PAR might go 2,000.

There are also low-voltage lamps and fixtures that can be used on a track. Although they cost more, they use significantly less electricity than regular reflector lamps, last just as long, heat up less, and provide a whiter, crisper light. Keep in mind, however, that a transformer is required in each fixture to step the house current down to the lamp's 12-volt level.

Finally, a track system shouldn't be contemplated without considering the use of a compatible dimmer, particularly with a single-circuit track. The ability to dim the lights can increase the versatility of a single-circuit track.

Cost can start as low as $50 for a 4-foot, single-circuit track with two lamps. Fixtures from different manufacturers cannot be mixed, so shopping around is necessary to find a system that fills the needs of a particular room.

"Some units are rather filmsy, and they're cheap," Bonvini said. "But if they're going to be mounted on the ceiling and left there, they're fine. I don't think you necessarily have to buy the top of the line."

How should track lighting be used? There are three basic ways, often intermixed:

Spotlighting (accent lighting) an object or group of objects such as a sculpture, wall-hung pictures, plants or collectibles. A spotlight or framing projector is usually used, although a floodlight may be needed for large objects or a grouping. Objects also often need two or even three different lights on them to provide proper shadowing.

Washing a wall with light to visually expand a room. This requires careful choice, spacing and aiming of the lamps, to avoid hot spots in the center and to create and even glow of light.

Directing light to a work area. Placement is doubly important to keep shadows off what is being worked on.

Overhead lighting not only adds to the background light in a room, but it can also vary the mood through the use of a dimmer switch or multi-circuit track. Each requires careful choice and placement of lamp to avoid glare, as well as proper lighting.

Eliminating glare generally requires running tracks a relatively short distance from the wall, usually 2 to 3 feet and all the way around the room if necessary. Such placement also allows the proper angle between the light and the wall or object that it is aimed at.

In selecting the lamp itself, the most important factors to consider are whether a spotlight or a floodlight is needed, and how much area it should cover. With either spot or flood, the greater the area covered, the less the intensity of the light in the center, even at the same wattage. A 75-watt R30 flood with a beam spread of 130 degrees will provide only about a third of the light 5 feet way that a 75-watt, PAR 38 flood with a 60-degree beam spread will.

Deciding how lamps should be placed is not as difficult as it might seem. With a helper on a ladder holding one or two flashlights or lanterns, try out different rough lighting placements before buying the track. Vincent Franzone, manager of Bowery Lighting in Garden City, N.Y., said he recommends getting a minimum number of lamps to start with, on the theory that less is safer, as well as potentially cheaper. "You can always come back and get another one," he said.

As for using flashlights or the lamps themselves to judge placement, Bonvini says "it's all shawow-casting. Everything makes a shadow. Depending on where the light is, that's where the shadow goes . . . Head-on lighting eliminates shadows. The more the light grazes on object, the more the shadows occur. All you have to do is plan where you want the shadows."

Finally don't forget that track lighting hangs from the ceiling. Ceilings less than 8 feet high are usually unsultable, partly because the fixtures can get in the way visually and partly because taller individuals can walk into them. Keep in mind that whatever track and fixtures you choose should blend into the room. "If you have a very contemporary room, lots of white and wood, black units are not suitable," Bonvini noted. In the same way, white fixtures might be suitably unobtrusive in traditional room with a white ceiling.