Halogen lamps are filled with an inert gas to suppress tungsten evaporation. However, due to the pressure limitations of the bulb, we cannot maintain high pressures. At a given filament temperature and pressure, the tungsten evaporation rate is fixed. The light loss caused by bulb blackening depends on the thickness of the tungsten deposit. The larger the bulb surface area, the thinner the tungsten layer. Therefore, the bulb should be made as large as possible, within the limits of the bulb's compressive strength.
Tungsten halogen lamps are a type of incandescent lamp. Halogen is introduced into the lamp, forming a compound with tungsten evaporated from the filament, thereby eliminating bulb blackening. Tungsten atoms evaporated from the filament can form a stable gaseous compound with halogen atoms, resulting in a low concentration of tungsten atoms near the bulb to deposit. This eliminates the light loss caused by gradual bulb blackening in conventional incandescent lamps.
In addition, the bulb can be made smaller, allowing for higher gas pressure within the lamp. The higher operating pressure inside the lamp further suppresses tungsten evaporation, extending the lamp's lifespan while ensuring consistent luminous efficacy.
Compared to ordinary incandescent lamps, tungsten-halogen lamps offer the following advantages:
At the same luminous efficacy, they offer a longer lifespan. Furthermore, at the same lifespan, tungsten-halogen lamps do not experience luminous decay due to bulb blackening, resulting in higher luminous efficacy at the same wattage.