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hi, can anyone tell me what high, medium and low ligh levels are in lumens or lux or candelas at gravel level instead of watts per gallon.

Last edited by dan76 at 22-Apr-2005 02:52

OH TOLEEDY!

Hi,
Specifically, No. However here are two sites that will
offer assistance in your computations:

http://www.fishprofiles.net/faq/plant-lighting.asp
and http://www.fitchfamily.com/lighting.html

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

thanks good links, but still looking for actual numeric values

OH TOLEEDY!

Hi,
I don't know that you are going to come up with any
specific values until you place your light meter in the
bottom of your tank. Because the amount of light varies
between tanks and tank depths, they don't publish anything
(that I know of) that says that "A" specific light will
deliver X lumens on the substrate of a given tank. There
are no standards.

You will either have to measure it with a meter designed
for diving and photography, or use the formulas in the
two sites I suggested.

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

hi frank , i was planning to use our lux meter from work to measure my light output at gravel level next time the tanks were empty. my tanks vary from 150mm to 600mm deep and i was hoping to get a number say 50 - 75 lux for low lighting etc and then i could add or remove lights to suit my plants.

OH TOLEEDY!

Hi,
Taking that reading while empty would give you a vague
idea what you had at the substrate surface, but remember
that as light travels through the air/water boundry you
have diffraction a loss, and as the light passes through
the water it is scattered by particulate matter, and as
it travels through the water it is absorbed by the water.
The red part is especially affected and absorbed. That is
why deeper tanks frequently require a bulb over 10,000K.
The blue part of the spectrum is the least affected.

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

*pulls out textbook*

Lux, lumens, etc. are useless measurements for plants, because they are normalized measurements specifically for the spectrum and intensities that humans can see. Plants need different amounts of a somewhat different spectrum. Lux meters measure the intensity of light only in this limited spectrum. Since aquarium bulbs are designed specifically to include frequencies outside what these meters can read, and to limit some that they do, you'll get a low measurement.

Optical watts are a measurement of the total optical power delivered across the whole spectrum. But, the watts that they use on the light bulb package is normally not the optical power, but the electrical power. This electricity is converted into heat as well as light, so only a percentage of the power ends up as usable light for your plants. The manufactures don't tell you how efficient their bulbs are, so we have no idea how much light they deliver.

In other words, there's no good scientific way to improve on the rules of thumb that you can find on this site without using a whole range of optical instruments. At work we just bought a spectral photometer for over $300000 US, and it still has a limited frequency range....

okay, thanks for your help everyone

OH TOLEEDY!