Old Bulbs = Algae

[Myka]

The reason for the algae growth is because most bulbs will actually have a fairly significant spectrum change. The spectrum goes red, yellow, white, blue. Not sure what red is (0K?), but yellow is 5000K, white is 10,000K, and blue is 20,000K. Everything in between is in between (go figure!). Whatever color it starts as (blue or white) it will fade towards the red spectrum. A new bulb being 20,000K may be 16,000K after a year. A new bulb being 10,000K may fade to 7,000K. Each bulb will fade a bit more or a bit less than the next bulb, and the ballast will also influence. The red spectrum encourages plant growth, that is why horticulture bulbs are low Kelvin like 5500-6500K.