The normaI operating life of pre-heat type fluorescent lamp is terminated when the cathode coating is completely stripped from the coiI filament.
In D. C. operation, the cathode spot moves from the line side of filament to the other expending it's coating.
We can measure the filament drop V
f-which is caused by the burned turns and shows the degrees of consumption.
It has been found that V
f has a linear performance characteristic.
Hence, within a comparativelly short period, measuring the incleasing speed of V
f and using a conversion coefficient obtained experimentaly, the life of A. C. supplied fluorescent lamps can be estimated.
Practically a rippled D. C. obtained by simple rectification of A. C. is preferable.
Our estimation of life shows agreement with actual and statistic data on the operating life of fluorescent lamps.
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