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Help me understand PAR readings please - and physically dimming lights possible?

605 Views 1 Reply 2 Participants Last post by  Hoppy
I get the numbers and all - but what is the most important, the number at the substrate or an average?

I asked this in another thread, but thought it deserved it's own. Going for low-mid light

Some fixtures (Finnex Ray2 for one) show very strong on the numbers at high mid tank, dropping to low light only after more than 18" (my tank is 20")

Others (like the Finnex FugeRay) have numbers that look doable at the top and middle, but at 20 inches the PAR is down to the mid teens. Is that enough? Just have the feeling that if I go this route and get a nice layer of frogbit growing that no light will get to anything else in the tank.

The TruLumen strips look good - a little pricey when you add up all the parts - but they can be dimmed. See conflicting info that they are either flamethrowers or over rated :) The shape seems nice for replacing the guts of a hood made for t8 bulbs.

Anyway, which numbers count the most?
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The numbers I use as "standards", 20-30 for low, 40-50 for medium, above 50 for high, are all based on PAR at the substrate level. If you wanted to use average PAR thoughout the tank it would be very difficult to measure, and I don't know what the numbers should be. The same is true for PAR at the midpoint of the tank. I use the PAR at the substrate because it is easy to measure, and because virtually all plants start their growth at the substrate. There may be a better way to characterize the light level, but someone else will have to figure that out.
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