Filament Design
1.Rated Voltage
The voltage at which the rated current,
brightness and average service life are specified is defined as the rated voltage.
2.Rated Current
The current, which flows when the rated voltage is applied to the lamp,
is defined as the rated current. Rated current tolerances are kept within +/-10%.
3.Brightness
The Brightness obtained when the rated voltage is applied to the lamp.
The brightness unit that is normally used in Japan and Europe is luminous flux(Lm).
In the United States mean spherical candlepower(M.S.C.P.) is used.
The relationship between M.S.C.P. and luminous flux is shown below.
4.Average Life
The average life (or laboratory life) is the average time until failure occurs with the rated voltage continuously applied,
with voltage fluctuation within +/-1% and without any shock or vibration.
Average lamp life is affected by the efficiency of the lamp. Generally,
a lamp with lower efficiency has a longer life.
Lamp efficiency can be calculated per the below formula.
5.Efficiency
Incandescent lamps will eventually fail due to evaporation of the tungsten filament.
High efficiency vacuum lamps will have a short average life due to accelerated evaporation of the tungsten filament caused by high filament temperatures.
To retard or slow the evaporation of the tungsten filament and to achieve longer life with higher efficiency,
gas-filled lamps should be used. For gas filling of lamps, Nitrogen(N2), Argon(Ar), Krypton(Kr), Xenon(Xe) or a hybrid gas mixture is generally used.