Domestic electric light sources

Domestic electric light sources

This animation shows the characteristics of domestic light sources, from traditional light bulbs to LED lights.



light source, lighting, lamp, traditional light bulb, halogen lamp, compact fluorescent tube, LED, light bulb, lifespan, filament, LED lights, LED chip, socket, fluorescent coating, electronics, electric current, electrode, light, Edison, Thomas Edison, heat radiation, electromagnetic, visible light, thermal conductivity, light switch, atomic orbital, resistance, particle physics, atomic physics, technology, physics

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  • - The tube is filled with noble gasses and mercury atoms. Mercury atoms emit UV photons which are absorbed by the fluorescent coating of the tube that emits visible photons instead. Its lifespan is about 10,000 hours (10 times the lifespan of a traditional incandescent light bulb).

In traditional incandescent light bulbs a tungsten filament emits light, which glows under electric current. The electric current causes the tungsten atoms to vibrate and release part of their vibrational energy by emitting photons.
The glass bulb is filled with inert gas: noble gasses or nitrogen gas, because, if exposed to oxygen in the air, the tungsten filament would burn almost instantly after switching the light on.

Incandescent light bulbs have low energy efficiency, only about 2% of the power consumed is emitted as visible light. Their lifespan is about 1,000 hours.

The principle of operation of a halogen lamp is the same as that of traditional incandescent bulbs: a tungsten filament glows under current, thus emitting light. Their lifespan is longer than that of incandescent light bulbs, as the noble gasses filling the bulb contain halogen atoms.
Tungsten atoms evaporated by the heat bond with halogen atoms; the resulting tungsten halides close to the filament break down due to the heat, and tungsten is deposited on the filament.

This slows down the thinning of the filament and increases the lifespan of the bulb. The temperature of the filament can also be increased, which results in greater energy efficiency.

In compact fluorescent bulbs the electrodes emit electrons. The tube is filled with noble gasses and mercury atoms. These are excited by the electrons and emit invisible, short-wave UV photons. The inner wall of the tube is covered with a fluorescent coating which absorbs UV photons and releases visible photons instead.

Mercury atoms emit photons because the electrons excite them, they are raised to a higher energy level and then, on 'falling back', they release some of their energy in the form of UV light. This is then converted to visible light by the fluorescent inner coating of the tube.

Compared to traditional incandescent light bulbs, compact fluorescent tubes have little heat loss, therefore they are more energy efficient: a 20 Watt CFL tube emits as much light as a traditional 100 Watt light bulb. Its lifespan is about 10 thousand hours, 10 times the lifespan of incandescent light bulbs.

  • - Its inner wall is covered with a fluorescent coating. The light emitted by the diode is of narrow wavelength, therefore it is colored. The light is absorbed by the fluorescent coating, which emits white light instead. In older types of LED bulbs red, green and blue diodes were used, the mixture of the three colors gave white light.

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