[MCSLABS]

In the process of building a hood for a 40g tank that is 20 inches deep. I an undecided as to how many lumens I will need to adequately grow these plants. I have been toying with the idea of 4, 6500k, 1600 lumen CFL's for a total of 6400 lumens. It should really light up the tank but I have no reference as to how much light I need.

 

[jeffkrol]

In the process of building a hood for a 40g tank that is 20 inches deep. I an undecided as to how many lumens I will need to adequately grow these plants. I have been toying with the idea of 4, 6500k, 1600 lumen CFL's for a total of 6400 lumens. It should really light up the tank but I have no reference as to how much light I need.

Lumens reallly don't apply well to planted tanks.
That said, since it is areadily available figure it has "some" use for comparisons w/ lights w/ similar spectrum's..
in your case it may be better to start w/ a watts/gallon figure since it is a "simplistic" tank geometry..
As to "color" don't assume 6500k is the most plant effective color..

So assuming 23W per bulb, you get 92W 2.3W/gallon

 

[jrygel]

A 6500k bulb will usually have a decent amount of output in the blue range of the spectrum (the first hump in the PAR curve on jeff's diagram), but little output in the red range that plants like. Some plants are affected by this loss more than others. That being said, assuming that the output is usable to the plants, 6400 lumens is probably plenty for a 40B. To put it in perspective, I have a DIY LED over my 90P (same footprint, but 2" deeper than 40B); I carefully selected the spectrum to more closely follow the PAR curve: it puts out around 7000 lumens and I get about 130 PAR at the substrate when it's cranked.

-Justin

 

[MCSLABS]

I was also considering these bulbs which put out 63 lumens per watt, running 42 watts. You can't compare apples to apples using watts as the common denominator, LED, Incandescent and CFL's all use varying amount of watts to produce the same amount of light.

I use 6500k on my house plants which seems to be adequate for proper growth. Keep in mind I am budget constricted.

I can put this together for about $20.

https://www.1000bulbs.com/category/150-watt-equal-compact-fluorescents-6500K/


More interesting stuff from the article

Planted Freshwater Aquariums: It is also important to note that freshwater algae also prefer more of the "blue" light so the excessive use of actinic blue lighting should be avoided in planted freshwater aquariums, as well the use of more blue nanometer or higher Kelvin Daylight (14,000K or especially 20,000K) should also be avoided in all but the deepest tanks or in tanks with heavy amounts of C02. Otherwise many freshwater plants may not be able to "out compete" against some algae such as hair algae.



Looky what I found, excellent article on, lumens, kelvin, par, nanometers

http://www.americanaquariumproducts.com/Aquarium_Lighting.html

 

[jeffkrol]

I was also considering these bulbs which put out 63 lumens per watt, running 42 watts. You can't compare apples to apples using watts as the common denominator, LED, Incandescent and CFL's all use varying amount of watts to produce the same amount of light.

I use 6500k on my house plants which seems to be adequate for proper growth. Keep in mind I am budget constricted.

I can put this together for about $20.

https://www.1000bulbs.com/category/150-watt-equal-compact-fluorescents-6500K/

True, but similar products "generally" have the same watt efficiency..
PAR is the best way to go.. Short of that you are left w/ lumens and watts..Knowing their weaknesses helps..
t5's and 8's spec out at close to 70-100 Lumens per watt..Ganted drive current (ballasts) play into this..
you could argue all day who's "guesstimate" is better.. but even "specs" right out of the box are not accurate..

Bump: you are also leaving out a lot of important info.. "bare bulb" cfls over a tank has an efficiency of probably less than 50% of the light going into the tank...
Easiest way is brooder reflectors and a cfl..

Using that as a starting point and assuming 6" of water.. 2 brooders over a 40 w/ 23w CFL's (assume 18" effective distance from rim of light to PAR sensor)..40-plus PAR
40 PAR is adequate for most plants..Second one will "spill over" to add PAR.

Putting 42W (assuming they fit) would pretty much double the PAR.. 80PAR at the substrate..

 

[MCSLABS]

I was considering about 2-3 of the 42 watt CFLs placed inside a hood configuration. I have a very curious cat that has already fell into the tank when I have taken the lid off of it.

 

[jeffkrol]

I was considering about 2-3 of the 42 watt CFLs placed inside a hood configuration. I have a very curious cat that has already fell into the tank when I have taken the lid off of it.

Hear you there..
So what are you planing on doing to make the lights more efficient?
no sense wasting a ton o light..

One suggestion if doing a box type hood.. and not planning any aluminum reflectors..

Paint it white inside w/ a good paint w/ a lot of Barium sulfate..
http://www.triticeaecap.org/wp-content/uploads/2011/12/Barium_Sulfate.pdf

some roofing paints are pretty good..but need to check.
Barium Sulfate itself is fairly cheap "if" you stay away from specialty or high purity powders..
Barium Sulfate Green Coloring Agent
Barium Sulfate - Rakuten.com
mix in your own paint..
It is not really necessary.. but a fun hunt..

 

[MCSLABS]

There is a construction build near my house that using foil lined radiant heat reflective barrier plywood. I picked up a fair amount of it to build the hood. I may still hit up Dollar General or Family dollar for some mirrors. I do have a Aqueon light in the tank now, its old and worn out. I'm considering buying a new one and adding it in there with the CFL's.

My PITA-C

 

[jeffkrol]

There is a construction build near my house that using foil lined radiant heat reflective barrier plywood. I picked up a fair amount of it to build the hood. I may still hit up Dollar General or Family dollar for some mirrors. I do have a Aqueon light in the tank now, its old and worn out. I'm considering buying a new one and adding it in there with the CFL's.

My PITA-C

cute cat.. And why I have all glass tops over my tanks..