Tuesday, October 7, 2008

Lighting for Aquatic Plants

I was just reading interesting article from ADA web site regarding their product NA light bulb spectrum. I realize that I have been mistaken for years. I was thought that photosynthesis is require red spectrum, but according to the article that only apply for land-based plants. If I understand correctly from the article, red light does not travel far under the water. This is the reason why NA light bulb temperature is around 7800K to 8000K.

"Amano: ...My red jacket looked black. What should have been red appeared black."

Graph shows light reduction rate depending on wavelength
(graph taken from ADA web site)

Also the light only appear bright for short period of time, typically 11:00 AM until 2:00 PM. During this time sunlight comes straight into the water. The entry angle before or after that period of time is too stiff thus the light reflected off the surface.

(graph taken from ADA web site)

Other important infos captured from the article are fluorescent bulb if turn on for 8 to 10 hours a day will last about half a year before the brightness rapidly decrease. As for Metal Halide (MH) bulb, it decrease after about 4000 to 5000 hours of lighting

You can read the full article from "Light Transmissivity in Water" and "The Light I Encountered Under Water"

Another interesting article is from Dennerle, it was mention that "The periods with bright light should always be of at least 4 hours’ duration. Plants will be unable to make effective use of shorter periods". I did accidentally verify this when I change my daily lighting period to 3hrs diffuse light + 3hrs intense (MH) light + 3hrs diffuse light, After two weeks I can see that my rotalla start shedding its leaves. This is when I found the Dennerle light article.

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