Fluorescent Lamps: Why Phosphor Drops Off in Efficiency & Mechanisms

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SUMMARY

Fluorescent lamps experience a drop in efficiency primarily due to the degradation of the electrode coating and the darkening of the glass. The electrodes, which initially emit more electrons when heated, lose their effectiveness as the coating deteriorates over time, making it difficult to sustain the arc. Additionally, the evaporated coating from the electrodes deposits on the inner surface of the glass, reducing the amount of UV light absorbed by the phosphors. This discussion clarifies that the efficiency loss is not primarily due to phosphor degradation, but rather due to these mechanical and chemical processes.

PREREQUISITES
  • Understanding of fluorescent lamp components, specifically electrodes and phosphors
  • Knowledge of the mechanisms of electron emission and arc sustainability
  • Familiarity with the effects of UV light on phosphor efficiency
  • Basic principles of chemical reactions involving phosphors
NEXT STEPS
  • Research the degradation mechanisms of electrode coatings in fluorescent lamps
  • Explore the impact of glass darkening on UV absorption in lighting technologies
  • Investigate different types of phosphors and their reactions in fluorescent lamps
  • Learn about advancements in fluorescent lamp technology to mitigate efficiency loss
USEFUL FOR

Electrical engineers, lighting designers, and anyone involved in the manufacturing or maintenance of fluorescent lighting systems will benefit from this discussion.

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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