SnakeIce

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 to prevent plant growth stagnation.

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


I hear that Europeans typically have less light over their tanks than Americans. How does the length of bulb use compare? 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?

Could we find a wattage and replacement schedule that would minimize cost of bulbs and electricity given a desired plant growth rate? Obviously a general expression would be of more use to the comunity than a specific solution.