This post is the first part of operation of all types of lamps and a comparative of parameters between the existent technologies. This part is about incandescent lamps.
Incandescent lamps
Standard incandescent
An electric current pass through a spiral tungsten filament, it produces heat with temperature high enough to emit light. In addition to that, this type has nickel (níquel) wires to sustain tungsten filament in extremities and conduct electric current. Molybdenum (molibdênio) wires support tungsten in center.
The lamp’s interior is filled with vacuum or inert gas, which does not react with other substances, this gas is nitrogen or a noble gas, like krypton, xenon or argon. The fusion point (melting temperature) of tungsten is 3422ºC, lamp’s temperature stays between 2200ºC and 3000ºC. Lasts in average 1200 hours, efficiency between 5 and 20% and luminous efficiency is between 15 and 25 lumens per watt (lm/W). The low yield is due to most part of energy used is converted in heat. The IRC (color reproduction index) is 100.
Halogens
These lamps also use tungsten filament and work like the standard incandescent. The main difference is that the inert gas has a quantity of halogen, it is used iodine, fluorine or bromine. Part of tungsten filament evaporates and these particles go to bulb’s internal walls. It because of that, standard incandescent lamps become darker and lose luminosity with time. In addition to have a bigger bulb to reduce luminosity loss.
The inert gas reduce filament’s evaporation rate. But halogen gas inside the lamp reacts with tungsten particles (W).
W+I_{2}\rightarrow WI_{2}
Thermal convection currents attract tungsten halide molecules to close to filament, where tungsten is deposited. However, the atoms are never deposited in the same place.
WI_{2}\rightarrow W+I_{2}
With the halogen gas, these lamps can be smaller than standard incandescents. This type of lamp has between 2000 and 4000 hours of lifespan. The luminous efficiency is 25 lm/W, IRC is 100. Halogen lamps can have many shapes and sizes. Usually are hotter than standard incandescent, though temperature depends on lamp’s power.
The next part will be about luminescent lamps.
