How Much Less Wattage from CFL?

DGalt

DGalt

AC Members
Jun 1, 2008
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Connecticut
I've heard this said a couple times (at least in reference to questions I've had) - that even though a CFL bulb may say 20 watts or whatever that it's not as efficient as an "old school" fluorescent bulb.

Unfortunately the only CF bulbs at the right K value that I can find are 26 watts (if someone can point out lower wattage ones please let me know), which brings my 15 gallon tank to about 3.5 WPG.

Now I didn't want to get anywhere close to this range because I didn't want to deal with a whole CO2 system and whatnot. So, my question is, about how much less efficient are the CFL bulbs (don't need a number, just a general idea)?
 
The relevant measure is luminous efficiency; this measures the lumens of visible light given off (lm) per watt of electricity (W) consumed. Standard incandescents have a luminous efficiency usually about 12-15 lm/W. CFL's are better at 45-60 lm/W. T12's are 80-85 lm/W. T8's are slightly better (80-95 lm/W) and standard T5's are even (a little) better at 90-100 lm/W. HO T5's are about as efficient as T8's. In all cases electronic ballasts are assumed; efficiency is considerably less with magnetic ballasts.

So, overall CFL's are about 50-75% as efficient as T8 or T5 fluorescents. If you have, say, two 23W CFL's over your 20 gallon, you have 2.3 W per gallon; however, you should actually calculate ((46 W X .5 to .75 = 23 to 34.5 W)/20 gal) = 1.2 to 1.7 W/gal when determining which plants you can grow.

Of course it should be noted that there a lot of other factors besides bulb efficiency, such as reflector design and distance of lamp from plants, that affect the amount of light actually reaching your plants. Additionally, high-color-temp and broad-spectrum fluorescents are less efficient than the numbers I gave, which are for household lamps, but as far as I know the proportionate efficiencies among the different lamp types remain the same.

I hope that was helpful! If anyone who knows more about lighting wishes to correct me please feel free; I just did a bit of googling and am by no means an expert.
 
I appreciate the comparisons, Noto. I use T8s mostly & like them for thier inexpensive availabilty & color. I have considered T5s & power compacts but don't have either so far, I'm too cheap & low tech.
 
great info! thanks so much. This is just what I was looking for. Luckily I bought the right bulbs :grinyes:
 
On a vaguely related note, if any of you are setting up 'shoplight' style fluorescent fixtures on your planted tanks and are looking for non-aquarium-trade lamps, I suggest checking out BlueMax lamps. I have four BlueMax HO T5's (really T6's, but they sell them as T5's) on one side of my 300 gallon and eight Sylvania 'Daylight' T12's on the other side, and the difference in plant growth is phenomenal. My vals on the BlueMax are 30" tall or more and are putting off plenty of plantlets, while the vals on the other side have hardly grown since being planted.

Unfortunately most of the lamps they offer are 36" and up, so they're not convenient for smaller tanks.
 
Also, I should point out that 'CFL' in the figures above refers to screw-in incandescent replacements, which I assume is what the OP was talking about. Two-pin high-output fluorescents are also called CFL's; I haven't found any luminous efficiency figures for them.
 
yea i'm referring to the spiral bulbs (which I think that site actually mentions)
 
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