Question

Efficiency for your bulb should have improved as the operating voltage increased. An even higher efficiency would have resulted if a still higher voltage were to be used to power the bulb. If melting of the filament were not an issue, discuss another limiting factor to improving efficiency by increasing voltage.

This is a concept of a lab called “Efficiency of an Incandescent Light Bulb” that I don’t understand. Please list a limitation to improving efficiency of a light bulb. I feel like I have given enough information in the question, so please do not give “not enough info” as the answer. Thanks!

Answer 1

The name incandescence itself mean an electromagnetic emission due to increase in temperature I.e heating. In incandescent bulb, the wire filament is heated by applying voltage and this heated filament emits electromagnetic spectra. There are two intrinsic limiting factor associated with incandescent lamps I.e

1) Maximum filament temperature that a filament can take without melting and

2) Luminous efficacy constrained by the nature of the light emission mechanism.

If melting of the filament were not an issue then still luminous efficacy can limit the efficiency of the incandescent bulb.

Luminous efficacy is defined as how well as light source like heat of the filament produces visible light and is given the relation

luminous efficacy = luminous flux / power

The efficiency of visible light generation is low in incandescent lamps because of low luminous efficacy which means that most of the input energy is not getting converting into visible light. It is rather getting converted into infrared light which is not relevant or useful for light application such as bulb. This infrared emission is considered as waste energy in incandescent bulb.

Filament can be considered as a black body radiator. Considering an ideal black body radiator, in order to produce visibly light most efficiently, the temperature must by around 6300 degree which is hotter than sun’s surface. Even at this temperature, most of the radiation is either in infrared or ultraviolet. This no known material can be used as a filament without melting at this temperature.

Thus luminous efficacy an important factor limiting the improvement of efficiency of the incandescent bulb by increasing voltage.

P.S higher voltage is to heat the filament more.