re: Measuring Effective Light

["Wayne J" <w.jones at sympatico_ca>]

Bill wrote:


The "Flourex Light'  thread reminds me of a similar discussion about a year
or so ago.  My contribution to that was to suggest that watts per gallon was
at best a rough estimate of the light available to plants, and that there
should be better measure.   Compact fluorescent technology apparently has
further weakened the wpg tool.

I had suggested that we hobbyists, through experimentation or calculation,
determine the amount of light energy from various bulb/ballast/reflector
combinations that actually reaches the bottom of the aquarium, measured at
various depths.  This could be made available in the form of a spreadsheet
and end for all time much of the questions about various kinds of light.
Almost, anyway.

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What you really need to calculate is fixture effciency as it relates to
aquariums. This would be difficult to do at the bottom of the aquarium as
different shaped aquariums would give different results with the same
fixture. It would not be hard to do at just below the water surface of an
aquarium. One could use a 55 gallon tank and put different fixtures on top
of it and then measure the average lumens landing on the horizontal plane
just below the water surface. For best results a lot of measurements would
have to be taken so that araes of concentrated light would not skew the
results. From that it would be possible to calculate an effciency using the
lumens from the lamp. The effciciency would probably be quite low. Surely
something below 50% even for the best fixtures. Once the effciency were to
be calculated it would then be a simple matter to predict the amount of
light that actually makes it into an aquarium. I would suggest using all 841
lamps for this sort of test so that the PAR/lumen would not have to be taken
into account.

Wayne