The Planted Tank Forum - View Single Post - what light level is this
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post #2 of (permalink) Old 01-17-2013, 04:30 PM
Planted Tank Enthusiast
Join Date: Jun 2012
Location: NE TN
Posts: 588
Originally Posted by Contrl View Post
I have a single t12 4foot 40 watt strip light over 2 15 gallon tanks. 12" deep and the light sits 5" above the tanks.

is this low? Medium?..... if I did a double tube t12 or t8 would I be high?

it does grow egeria densa like a weed,,,, but then again that is a weed...
I used my Lux meter on an old 2 bulb T12 fixture with new bulbs done in air not in water. Here's the readings I got:

2 bulb T12 fixture on the 2nd no foil reading I turned the bulb slightly and noticed it got brighter so it's more accurate.
Height Foil Lux/Par --- No Foil Lux/Par -----No Foil Lux/Par
15 -------- 381/50.1 --------- 344/45.3 ------------ 372/49.0
20 -------- 278/36.6 --------- 248/32.6 ------------ 275/36.2
25 -------- 210/27.6 ----------190/25.0 ------------ 202/26.6
30 -------- 164/21.6 ----------145/19.1 ------------ 154/20.3

For background, I was also trying to see if an aluminum foil lined fixture was better than just a regular white painted surface shop light. Comparing the 1st column with the 3rd column appears it's not worth the effort.

I think you can use 1/2 the value to get an guesstimate of what 1 bulb would be. Also, Hoppy says it will get at least 10% more than my data indicates - due to the slight focusing effect of the air to water interface. Unfortunately I didn't do a reading for 10" height and Hoppy didn't chart this fixture but maybe this will help at least a little bit.

This info was originally posted in this thread but I've corrected the PAR values here. In that thread the PAR was NOT based on the corrected conversion number: Lux readings for T12 & T8 Aquarium Hood
I see I need to correct that thread so the PAR values are correct.
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