# Lumens vs. Light Temperature (K)



## Aioros (Nov 17, 2010)

I have seen some bulbs that have specs like 300 Lumens with a color temperature of 4000k and say a 230 lumens with 6500k. Which one would be more efficient? I know there are many variables regarding the choice of light for my specific tank, but in general which one looks more promising. I guess I'm confused about lumens.


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## Hoppy (Dec 24, 2005)

Lumens are the measure of the total light emitted by the bulb. "Color temperature" is a number chosen largely to help sell the bulb, but very roughly related to what temperature a "black body" would be heated to to emit a similar spectrum of light. Color temperature has no relationship to the efficiency of the light. (It is certainly related to the efficiency of the marketing people at the bulb manufacturer.)


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## Wasserpest (Jun 12, 2003)

More lumens means the bulb appears brighter to the human eye.

Efficiency would be lm/w, so you would divide the lumen number by the electrical power usage of the bulb and the higher that number, the more efficient is the bulb.

There are some other aspects to throw in when it comes to planted tanks, like how many of those lumens make it into the tank (reflector design) and how useful are those lumens for photosynthetic activity of our plants (PAR).


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## stewardwildcat (Feb 24, 2010)

Wasserpest is correct, Lumens is corrected for how the human eye sees. So Lumens/w is the efficiency for lighting up your tank so you can see it, but PAR/w is the efficiency the light available to be used by the plants in your tank.


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