WPG versus bulb age

SnakeIce

AC Members
May 4, 2002
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North Ga, USA
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Frederick
Does how long you use a fluorescent light bulb change the effective lighting over a tank?

I have a 20 gallon with the eclipse 2 hood over it. I'm using the stock 2x 15 watt fixture in the hood. I have had to use two of the same brand and type bulbs and not use them for more than 6 months to get growth out of my plants. To even out how my plants grew I shifted the replacement of one bulb by 3 months so I wouldn't have either two brand new bulbs or two six month old bulbs. By only using 1.5 WPG I had to keep up with the bulb replacement and change them before all use possibly had been gotten out of them.

So is 2-2.5 wpg recommended because there is more room for efficiency decay due to age or are people after what I had with 1.5WPG but proportionally amped up

Based on my experience with my 20 gallon tank could one 2.5 WPG setup be considered high light while another identical setup (one using bulbs for 4 months and the second for a year just to stretch the comparison) be considered medium light just because of the bulb replacement schedule?
 
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I guess it doesn't matter that much. Just one of those tangents I go on sometimes.
 
IME that flutuates a lot with the tubes. Some decay/degrade fairly slowly, others nuch more steeply. My long-time favorites (Tritons) drop a bit in the first 100 hours, then hardly at all until they turn off at 18-24-29/30 months. The Phillips 6500K which I use for utility loses effectiveness if if I keep it on my 2WPG tanks more than a year. but replacing one of two tubes every six months stays pretty even.
 
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