Lighting Question

**csmith** · 05-07-2010, 03:37 AM

Will a 24 watt T-5 bulb over a 20 gallon tank put me into low light territory? My options are 1x24 (1.2 wpg) on the tank or 2x24 (2.4 wpg) hanging. My goal is a medium-ish rate of growth (stems, crypts, dwarf sag) and if the 1 bulb can get me there I'd prefer it, but hanging a 2x24 is feasible. Either way there will be an inconvenience, waiting for the glass lid to come in or having to build the arms. Opinions?

**dutchy** · 05-07-2010, 09:19 AM

I would go for 1 x 24 Watt. One T5 with reflector over a small tank gives a pretty intense light. if you look at Hoppy's PAR measurement chart on
http://www.plantedtank.net/forums/li...t5-t12-pc.html you will find out that even with one bulb you will have high light.

regards,
dutchy

**Tug** · 05-07-2010, 11:29 AM

Hi all,
That is one nice chart by Vaughn showing PAR. We should have one around here as well. Here it is, http://www.barrreport.com/showthread...or-T5HO-lights

I don't grow all the plants mentioned in the OP, but it is adding CO2 that makes all the difference. Most plants will grow under one T5HO, you might find you even need to add a little window screening to block back some light. One bulb wont give you the best spread. Hanging them above the tank wouldn't hurt in either case.

**aquabillpers** · 05-09-2010, 12:40 AM

Even one T5 over a 20 gallon tank will move you into the high light arena.

Bill

**csmith** · 05-09-2010, 02:59 AM

I'm not sure why it's such a difficult thing to grasp (for me) that watts per gallon is a moot point now-a-days. T-5 has T-5 power, MH has MH power, etc. and watts are just what powers them. Thanks for the answers guys, I'll try to keep it straight now.

Hoppy = Vaughn = VaughnH?

**Tug** · 05-09-2010, 12:50 PM

Sorry, I linked to my post and not the one by VaughnH. That has been fixed.

I should also say, just to be contrary, I kind of like the hanging light idea. The PAR values are about the same if you can raise the two T5HO's far enough above the tank and the raised light would provide a more even spread.

**csmith** · 05-09-2010, 04:55 PM

Originally Posted by Tug

Sorry, I linked to my post and not the one by VaughnH. That has been fixed.

I should also say, just to be contrary, I kind of like the hanging light idea. The PAR values are about the same if you can raise the two T5HO's far enough above the tank and the raised light would provide a more even spread.

It would seem that way. Using both links you guys gave, It kind of comes across as if you raise any T-5's by 10 inches it'll halve the PAR output but increase spread. Atleast that works out according to these charts for my 20 and 55. Thanks again guys.

**Gerryd** · 05-09-2010, 05:44 PM

Originally Posted by csmith

I'm not sure why it's such a difficult thing to grasp (for me) that watts per gallon is a moot point now-a-days. T-5 has T-5 power, MH has MH power, etc. and watts are just what powers them.

Hi,

Because watts does not equate to a LIGHT unit of measure....

You hit it on the head with your last statement. Watts are just what POWERS the bulb NOT what THE PLANTS UTILIZE.. So the two are not really related.

PAR is an accepted method to measure the actual LIGHT OUTPUT across ALL bulbs and types.

So, a PAR value of 30-50 is lower light no matter if from 1 T-12 bulb or a MH suspended 60" above the surface

Even though the t-12 is 2 wpg and the MH is 5 wpg.

Watts per gallon is MEANINGLESS when measuring actual light output that THE PLANTS receive.

Regardless as well of the way it looks to our eyes...

Hope this helps.