Fluorescent Lamps: Why Phosphor Drops Off in Efficiency & Mechanisms

  • Thread starter Charles123
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In summary, the drop in efficiency of phosphor during use can be attributed to two main factors. Firstly, the coating on the electrodes in the bulbs degrades over time, leading to a decrease in electron emission and ultimately causing the arc to not be sustained. Secondly, the darkening of the glass due to the evaporation of the electrode coating and subsequent deposition on the inside of the glass also contributes to a decrease in UV absorption by the phosphors. Additionally, depending on the type of phosphor used, other reactions can also occur, further impacting its efficiency.
  • #1
Charles123
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Why phosphor drops off in efficiency during use? By what mechanisms?
Thank you
Regards
 
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  • #2
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.
 
  • #3
Thank you for your answer.
So it's not due to degradation of phosphor?
Regards
 
  • #4
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
 
  • #5


There are a few reasons why the efficiency of phosphors in fluorescent lamps may decrease over time. One possible mechanism is the buildup of impurities on the surface of the phosphor coating, which can decrease its ability to convert electrical energy into light. This can happen due to factors such as dust, moisture, and chemical reactions with other materials in the lamp.

Another mechanism that can contribute to decreased efficiency is the degradation of the phosphor material itself. Phosphors are typically made of rare earth elements, which are known to have limited lifetimes and can degrade under the high temperatures and pressures inside a fluorescent lamp.

Additionally, the constant bombardment of electrons on the phosphor coating can cause physical damage, leading to decreased efficiency. This phenomenon is known as electron bombardment damage and can occur due to the high voltage and current used in fluorescent lamps.

In summary, the decrease in efficiency of phosphors in fluorescent lamps can be attributed to factors such as impurities buildup, material degradation, and electron bombardment damage. Regular maintenance and proper handling of the lamps can help mitigate these issues and maintain their efficiency over time.
 

1. What is the main reason for phosphor dropping off in efficiency in fluorescent lamps?

The main reason for phosphor dropping off in efficiency in fluorescent lamps is due to the degradation of the phosphor coating on the inside of the lamp. This can be caused by several factors, including exposure to high temperatures, UV radiation, and ion bombardment from the discharge in the lamp.

2. How does temperature affect the efficiency of phosphor in fluorescent lamps?

High temperatures can cause the phosphor coating on the inside of the lamp to break down, resulting in a decrease in efficiency. This is because the heat can alter the chemical composition of the phosphor, making it less effective at converting UV light into visible light.

3. What role does UV radiation play in the degradation of phosphor in fluorescent lamps?

UV radiation can cause the phosphor coating to age and become less efficient over time. This is because the high energy of UV light can cause chemical reactions in the phosphor, leading to a decrease in its ability to convert UV light into visible light.

4. Can ion bombardment affect the efficiency of phosphor in fluorescent lamps?

Yes, ion bombardment from the discharge in the lamp can cause physical damage to the phosphor coating, leading to a decrease in efficiency. This is because the ions can physically remove or damage the phosphor particles, making them less effective at converting UV light into visible light.

5. What techniques can be used to improve phosphor efficiency in fluorescent lamps?

There are several techniques that can be used to improve phosphor efficiency in fluorescent lamps. These include using higher quality phosphor materials, optimizing the lamp design to reduce heat and UV radiation exposure, and implementing protective coatings to reduce ion bombardment. Regular maintenance and replacement of old lamps can also help maintain the efficiency of phosphor in fluorescent lamps.

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