Fluorescent Lamps: Why Phosphor Drops Off in Efficiency & Mechanisms

[Charles123]

Why phosphor drops off in efficiency during use? By what mechanisms?
Thank you
Regards

 

[rollcast]

A couple of reasons I can remember:

The electrodes in the bulbs have a coating which makes it easier to produce the arc by emitting more electrons when heated compared to the tungsten electrode and over time this coating degrades until eventually the arc cannot be sustained.

This leads on to number 2 which is the darkening of the glass, as the coating is evaporated off the electrodes it is then deposited on the inside of the glass which then causes less UV to be absorbed by the phosphors.

 

[Charles123]

Thank you for your answer.
So it's not due to degradation of phosphor?
Regards

 

[rollcast]

Thank you for your answer.
So it's not due to degradation of phosphor?
Regards

You also can get reactions with the phosphor but there's a whole load of them depending on the phosphor: link