A Question on Light Penetration of CFL Bulbs
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Old 02-22-2015, 06:53 PM   #1
birbaliktanki
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A Question on Light Penetration of CFL Bulbs


Hi,

I'm using 5 cfl bulbs (15 watts each, 75 watts total) on a 30 gallon tank, about 18" height. I would like to decrease the lighting to about 60 watts total as I'm having various algae issues. I also read from here about the importance of having adequate lighting spread. I don't know if I should use 3 bulbs with 20 watts each or go with 5 bulbs with 10 watts each. Does a bulb with 20 watts have more light penetration than 2 bulbs with 10 watts each? I guess this can be easily answered with a par meter but I don't have one and have no plan to buy one either.

Appreciate your help.
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Old 02-22-2015, 11:47 PM   #2
Raymond S.
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If that is a 29g tank 30" long then three @ 20W is good.
One @ 14W is best for a 10g while two @ 14W is good for a 20L.
So the extra depth will take more, but it's only a couple more inches longer than that 20L.
And not twice as tall so the three @ 19-20W may still be a little high.
But see if it produces much algae. I would not use three @ 26W on there.
If you skim read over this thread till you get to parts which apply it may help.
http://www.plantedtank.net/forums/sh...ad.php?t=85667
But if that is a 30L tank(36"x12"x16") then I would still use three @ 20W but I'd raise them up about 4-6" off the top of the tank.
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Old 02-23-2015, 02:21 AM   #3
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Thanks for your help. Tank is 30 x 18 x 18". How about if I use 5 bulbs of 10 watts each for better light spread? My concern with this is the light reaching the substrate the same as using 3 bulbs of 20 watts each?
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Old 02-23-2015, 04:06 PM   #4
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A 20L tank is about 10" from top to the top of the sub. You are adding another 6".
Look on the link at post # 21 diagram #7.
It shows approximately what you will have/w 14W bulbs. That is way too high of light without injected CO2. The distance is about the same as your tank if the light is right at the top. You will need to raise it some to lower the PAR.
A 20L tank does just fine/w two 13W bulbs(vertical) and it is 24" long. That extra 4"
won't make any difference. If you add other bulbs, the light multiplies by it's self when the beams cross. If you put three 8" dome reflectors and raise them about 6" up from the top of the tank it may work out well. But you may need to raise them more if you start getting algae very quickly. Three bulbs @ 10W.
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Old 02-23-2015, 05:43 PM   #5
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Quote:
Originally Posted by birbaliktanki View Post
Thanks for your help. Tank is 30 x 18 x 18". How about if I use 5 bulbs of 10 watts each for better light spread? My concern with this is the light reaching the substrate the same as using 3 bulbs of 20 watts each?
Lower wattage = less penetration. You'll have better spread w/5 10w but the light source will be weaker near the bottom of the tank.

How big are the domes? A larger dome will help the spread, but also loses a little when it comes to penetration. The diagrams in the thread Ray linked dont include this particular variable. So for example 14 watts in a 6" dome wont be the same as in a 12".

Three 20 watts in 8" - 10" domes may give you the best of both worlds. Good spread and still adequate penetration. Then like Raymond said you can fine tune by adjusting the height.
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Old 02-23-2015, 07:01 PM   #6
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im using finnex solar duo refugium cliplight which houses 1 bulb per fixture. the height is not adjustable.
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