The blackening of a used light bulb is actually a sublimation phenomenon, which is because the filament of an incandescent bulb is usually made of tungsten.
When the light bulb gets hot, the tungsten filament sublimates due to heat and turns into gas. These heat-containing gases solidify when they encounter the low-temperature parts of the inner wall of the bulb, forming black tungsten substances that gradually adhere to the inner wall of the bulb.
The service life of light bulbs is usually limited by the sublimation problem of tungsten filaments. When a light bulb is heated, the tungsten filament sublimates and gradually becomes thinner, and may eventually burn out. Once the inner wall of a bulb turns black, its lifespan will be shortened. Therefore, the average lifespan of an incandescent bulb is usually only about 1,000 hours.
Incandescent lamps have many advantages, such as small light source, good color rendering, and proximity to natural light. Moreover, after multiple processing and designs, many different types of bulbs have been derived. However, incandescent lamps also have drawbacks. For instance, when they are powered on, their temperature rises, and they only convert 2% of the electrical energy into light energy, while the majority of the other electrical energy is wasted in the form of heat.
To sum up, the blackening of a light bulb is a sublimation phenomenon. If there is no problem with the bulb itself, it can still be used. However, considering the low efficiency and short lifespan of incandescent bulbs, it might be necessary to consider replacing them with other types of bulbs, such as LED bulbs, which have higher energy efficiency and a longer lifespan.
Luminaire lighting
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