Fluorescent Lamps: Why Phosphor Drops Off in Efficiency & Mechanisms

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Phosphor efficiency in fluorescent lamps declines due to several mechanisms, primarily the degradation of the electrode coating, which reduces arc sustainment over time. As the coating evaporates, it darkens the glass, leading to decreased UV light absorption by the phosphors. This process does not primarily stem from phosphor degradation itself, but rather from the interactions and reactions that can occur with the phosphor materials. Understanding these mechanisms is crucial for improving fluorescent lamp longevity and performance. Overall, the efficiency drop is linked more to electrode and glass changes than to the phosphors directly.
Charles123
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Why phosphor drops off in efficiency during use? By what mechanisms?
Thank you
Regards
 
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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.
 
Thank you for your answer.
So it's not due to degradation of phosphor?
Regards
 
Charles123 said:
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
 

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