Baby with Lamp

Incandescent Lamps

The incandescent lamp dates back over one hundred years to Thomas Edison's original invention. Essentially, an incandescent lamp produces light when its filament is heated by an electric current, causing it to glow or "incandesce." Normally, the filament is made of a coiled or doubly-coiled tungsten wire.

The advantages of incandescent lamps include a low initial cost, high color rendering ability and general ease of operation; dimming is easy and a variety of wattages can be used in the same socket.

There are hundreds of variations of wattages, sizes, shapes, and colors. The everyday incandescent lamp is called a "general service" lamp or an "A" lamp.

Reflector ("R") Lamps

A general service lamp emits light in all directions. However, "R" lamps were introduced with a built-in reflector to collect and focus the light from the filament, giving a simple, directional characteristic to the beam.

The Energy Policy Act (EPACT) of 1992 targeted "R" lamps and other incandescent type lamps that did not meet the new minimum efficiency ratings. As a result, very few "R" lamps are still sold today.

PAR Lamps

A more efficient, commonly used reflector lamp is the PAR lamp. PAR stands for Pressed Glass Aluminized Reflector. These lamps are formed from two pieces (lens and reflector) of pressed, thick, heat resistant glass and are able to be used outdoors in the rain or snow.

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Halogen Lamps

Tungsten halogen lamps are basically incandescent lamps that operate at higher pressure and temperature than standard incandescent lamps, producing a whiter light and longer life. The "tungsten" part of the name comes from the filament material - tungsten. The halogen part refers to the type of chemical additive that bestows the lamp with its special properties.

Another way halogen is an improvement over standard incandescent is in light output. Incandescent lamps have a tendency as they burn to slowly deposit their allotment of tungsten onto the glass bulb, turning the bulb black. This black coating blocks some of the light from coming out of the bulb. Eventually, the filament gets thinner, breaks, and the lamp fails.

The halogen gas in the lamp significantly reduces the deposition of evaporated tungsten onto the glass bulb. No bulb blackening = more light!

Infrared Coating

The most energy efficient halogen lamp is one with an infrared reflective (IR) coating. The coating redirects the infrared energy back onto the filament, while letting the visible energy pass through the coating. The redirected (or recycled) infrared energy improves the output to approximately 82% infrared heat and 18% visible light - instead of the 90-10 heat to light ratio of a standard lamp.

The Halogen Cycle

1Tungsten atoms evaporate from filament.

2Tungsten atoms combine with halogen atoms.

3The resulting compound returns to the filament, redepositing tungsten.

4Halogen atoms are released to recombine with other tungsten atoms.

There are two general families of halogen lamps: line voltage and low voltage. Line voltage simply means the voltage available at the wall outlet in your home - 120 volts in North America. Europe and much of the rest of the world uses 220 volts. Low voltage usually means 12 volts (and that's the same all over the world).

Here are some examples of line voltage halogen lamps:

Line Voltage halogen lamps tend to be mostly PAR lamps, but can also be tubular-shaped.

Low voltage halogen lamps have shorter, fatter filaments compared to line voltage lamps. Due to this, the lamps can be smaller in size and the light more precisely aimed.

Halogen lighting can provide dramatic downlighting effects

DramaLow voltage halogen lighting can be used to create dramatic contrast - calling attention to featured artwork in a space.

Halogen Applications

Retail highlighting merchandise either from track or recessed luminaries

Museums lighting artwork and sculpture

Residential track lighting, recessed lighting

Decorative pendant lights over surfaces

Task Lighting reading and other tasks

Since low voltage lamps operate at 12 volts, they need a transformer to reduce or "transform" the 120 volt power down to 12 volts. Even though this adds to the cost, these lamps can provide lighting effects unattainable with line voltage types.

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Dimming incandescent lamps in the home can substantially increase lamp life as well as save energy.

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The Life of a Lamp

Lumen values decrease over time as the lamp is operated. In incandescent lamps, this is due primarily to the deposition of tungsten from the filament on the glass bulb - darkening it and reducing the transmission of light. When a standard incandescent lamp is near its end of life, it may only be providing 80% of the light it produced when new.

For incandescent lamps, this decrease in lumens (called "lumen depreciation") is noted at a point that is 70% of the rated life of the particular lamp. If a lamp were rated for 1000 hours life, then the rating point to denote lumen depreciation would be at 700 hours.

Long Life vs. Light Output: The Trade-off

Most general purpose incandescent lamps are designed to operate at 120 volts. Life of incandescent lamps can be extended beyond the official rating by operating the lamp below its rated voltage. For example, at 110 volts, the lamp would last over 3 times as long as its rated life.

The downside is that the light output drops by 25%. For higher-than-rated-voltage operation, the opposite occurs. At 130 volts, this same lamp would only last about one-third as long as the rated life, but the light output increases by 30% as compared to the 120 volt rating.

Suggestion It is impractical to have 130 volt service or any other "higher-than-rated-voltage-operation".
What we sometimes explain is the possible use of 130v lamps operated on 120 volts. It's more usual to have 115v or 120v service at a residence. 130 volt lamps do exist but would have to be special ordered. The result is an extension of lamp life, and also a warming of color temperature - a "yellower effect.