Flourescents changing spectrum?

[dnjan]

A post in another thread mentioned that florescent lights would change spectrum over time, and that this spectrum change could contribute to a nuisance algae outbreak.

I'm not sure I follow this. I can see how some parts of the florescent spectrum could decrease over time, but not how other parts could increase. So if nothing is increasing, how could that cause a nuisance algae bloom? And as far as new wavelengths appearing, wouldn't that be akin to creating matter? (for a florescent bulb?)

Explanations/clarifications appreciated.

 

[Witfull]

as a bulb gets used the phosphurs burn and as they do they degrade. this causes a shift in spectum. its not creating matter is a rearrangement so t speak. as a bulb ages the spectrum will shift from the shortwavelengths to longer ones (blue to red) nuisience algaes will thrive in a more yellow/red spectrum thus the older the bulb the ]more the envonment is skewed towards the NA liking.

 

[dnjan]

Is it a changing of the phosphor compounds? I thought that the "flourescence" was element-specific.