Fluorescent Lamps:
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Components of a fluorescent lamp

The phosphor coating determines the lamp's color and light output. It is the most expensive ingredient in the lamp and the one that has seen the greatest improvements over the years. The phosphors used in today's T8 lamps are better than the ones used in T12 Cool White lamps.

The cathodes are used to provide electrons for the electrical discharge. They have a powder called "emission mix" which gets used up as the lamp burns, resulting in the lamp flickering (trying to start) or failing to start as it reaches end of life.