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post #6 of (permalink) Old 09-27-2012, 11:50 PM
Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Posts: 11,721
Here is a really basic PAR lesson:

People see yellows and greens best.

Plants see reds and blues best.

PAR is a measure of the reds and blues.
A high PAR light may not make the tank look great, because it usually does not have much of the greens and yellows we see. If you can arrange 3 of those light fixtures over the tank I would get 2 bulbs with high par, and use one of the 6500K bulbs so it will make the fish look better.

Light is a lot of different colors. A K value is just an average of what the light looks like to our eyes, it does not tell you what colors go into making it look like that.

WPG worked pretty well when there were very few styles of bulb to choose from, but the field is so wide open now that it is much better to go by the PAR info, if you can find it. Reflectors were not all that great then, either. Now you can get reflectors so good that they make a low light bulb (a T-8) work as well as a much better medium light bulb (a T-5NO).
If you are stuck going with WPG, this was worked out when T-12 and T-8 bulbs were most commonly used. There were hints even then that the colors produced by the bulbs made a difference, and about the only info commonly available about most lights was the K value.
This does not work so well with the fluorescent bulbs that are coiled into a spiral. A lot of the light hits the other parts of the spiral, and not the tank. A straight bulb with a good reflector puts more light into the tank, loses less to getting absorbed.

I understand low budget, but there are 2 parts to that equation:
Buy the cheapest, then pay more for the power because you had to get a more powerful fixture, 'cause half the energy is wasted.
Buy better, then pay less to run it because more of the power it uses is turned into light that actually works by hitting the plants (not lost or getting absorbed by cheap reflectors), and is the right wavelength to make them photosynthesize.
Diana is offline  
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