Voltage, light output, and lifetime

ncandescent lamps are very sensitive to changes in the supply voltage. These characteristics are of great practical and economic importance.

For a supply voltage V near the rated voltage of the lamp:

Lamp bases

Very small lamps may have the filament support wires extended through the base of the lamp, and can be directly soldered to a printed circuit board for connections. Some reflector-type lamps include screw terminals for connection of wires. Most lamps have metal bases that fit in a socket to support the lamp and conduct current to the filament wires. Continue reading “Lamp bases”

Bulb shapes, sizes, and terms

Incandescent light bulbs come in a range of shapes and sizes. The names of the shapes may be slightly different in some regions. Many of these shapes have a designation consisting of one or more letters followed by one or more numbers, e.g. A55 or PAR38. The letters represent the shape of the bulb. The numbers represent the maximum diameter, either in eighths of an inch, or in millimetres, depending on the shape and the region. Continue reading “Bulb shapes, sizes, and terms”

Power of Light Bulb

Incandescent light bulbs are usually marketed according to the electrical power consumed. This is measured in watts and depends mainly on the resistance of the filament, which in turn depends mainly on the filament’s length, thickness, and material. For two bulbs of the same voltage, type, color, and clarity, the higher-powered bulb gives more light. Continue reading “Power of Light Bulb”

Light Bulb Electrical characteristics

Incandescent lamps are nearly pure resistive loads with a power factor of 1. This means the actual power consumed (in watts) and the apparent power (in volt-amperes) are equal. The actual resistance of the filament is temperature-dependent. The cold resistance of tungsten-filament lamps is about 1/15 the hot-filament resistance when the lamp is operating. Continue reading “Light Bulb Electrical characteristics”

Halogen lamps

The halogen lamp reduces uneven evaporation of the filament and darkening of the envelope by filling the lamp with a halogen gas at low pressure, rather than an inert gas. The halogen cycle increases the lifetime of the bulb and prevents its darkening by redepositing tungsten from the inside of the bulb back onto the filament. Continue reading “Halogen lamps”

Bulb blackening

In a conventional lamp, the evaporated tungsten eventually condenses on the inner surface of the glass envelope, darkening it. For bulbs that contain a vacuum, the darkening is uniform across the entire surface of the envelope. When a filling of inert gas is used, the evaporated tungsten is carried in the thermal convection currents of the gas, depositing preferentially on the uppermost part of the envelope and blackening just that portion of the envelope. Continue reading “Bulb blackening”

Reducing filament evaporation

One of the problems of the standard electric light bulb is evaporation of the filament. Small variations in resistivity along the filament cause “hot spots” to form at points of higher resistivity ; a variation of diameter of only 1% will cause a 25% reduction in service life. The hot spots evaporate faster than the rest of the filament, increasing resistance at that point—a positive feedback which ends in the familiar tiny gap in an otherwise healthy-looking filament. Irving Langmuir found that an inert gas, instead of vacuum, would retard evaporation. Continue reading “Reducing filament evaporation”

Light Bulb Filament

The first successful light bulb filaments were made of carbon (from carbonized paper or bamboo). Early carbon filaments had a negative temperature coefficient of resistance – as they got hotter, their electrical resistance decreased. This made the lamp sensitive to fluctuations in the power supply, since a small increase of voltage would cause the filament to heat up, reducing its resistance and causing it to draw even more power and heat even further. Continue reading “Light Bulb Filament”

Light Bulb Construction

Incandescent light bulbs consist of a glass enclosure (the envelope, or bulb) with a filament of tungsten wire inside the bulb, through which an electric current is passed. Contact wires and a base with two (or more) conductors provide electrical connections to the filament. Incandescent light bulbs usually contain a stem or glass mount anchored to the bulb’s base which allows the electrical contacts to run through the envelope without gas/air leaks. Continue reading “Light Bulb Construction”

Efforts to improve efficiency

Due to the measures noted above, there have been recent efforts to improve the efficiency of incandescents. For example the consumer lighting division of General Electric announced that they are working on a “high efficiency incandescent” (HEI) lamp, which they claim could ultimately be as much as four times more efficient than current incandescents, although their initial production goal is to be approximately two times more efficient. Continue reading “Efforts to improve efficiency”

Cost of lighting

The desired product of any electric lighting system is light (lumens), not power (watts). To compare incandescent lamp operating cost with other light sources, the calculation must also consider the lumens produced by each lamp. For commercial and industrial lighting systems the comparison must also include the required illumination level, the capital cost of the lamp, Continue reading “Cost of lighting”

Light Bulb Commercialization

Joseph Wilson Swan (1828–1914) was a British physicist and chemist. In 1850, he began working with carbonized paper filaments in an evacuated glass bulb. By 1860 he was able to demonstrate a working device but the lack of a good vacuum and an adequate supply of electricity resulted in a short lifetime for the bulb and an inefficient source of light. By the mid-1870s better pumps became available, and Swan returned to his experiments. Continue reading “Light Bulb Commercialization”

Early pre-commercial research of light bulb

In 1802, Humphry Davy had what was then the most powerful electrical battery in the world at the Royal Institution of Great Britain. In that year, he created the first incandescent light by passing the current through a thin strip of platinum, chosen because the metal had an extremely high melting point. It was not bright enough nor did it last long enough to be practical, but it was the precedent behind the efforts of scores of experimenters over the next 75 years. In 1809, Davy also created the first arc lamp by making a small but blinding electrical connection between two carbon charcoal rods connected to a 2000-cell battery; it was demonstrated to the Royal Institution in 1810. Continue reading “Early pre-commercial research of light bulb”