uh question!? about lights

[StirCrazy]

Originally Posted by qwiksilver

So, for sake of simplicity and reliability, lumens are an appropriate means of measurement.

the problem with using lumens is that it is a measurment of a narrow band of visable light only and it is an average over a given area. PAR, PUR ect which is the real importance also incorperates light readings that are not in the narrow band and are also usable by the corals or plants.

the real problem that wreaks havic with lumen measurments comes into play when trying to compare lights that are composed of different spectrums. say you have two lights that are both a final output of 10000K but to get there they use different combanations of red, green and blue. sence lumen measurment is primarly of the green spectrum (if not all in the green if I remember corectly) you can have one light that is heavy in green with just enuf bule and red to balance it, or a light that is heavy in red and blue with a little green. the first bulb will measure a lot higher lumen out put than the latter but the latter will supply a higher PAR rating than the first. so this is why the lumen rating doesent work as good as we would think as I have found out from my own testing and that other have also confirmed in there testing. another problem with a lumen meter is it assumes that the light output is totaly uniform so in reality it is a hypothetical reading, where when I use my PAR meter it is a given that it is a pin point measurment that has to be in the same conditions for each measure, but because it measures the whole usable spectrum the make up of the light isn't as much as a factor as with a lumen meter.

what a lumen is good for, and I used to use it for this purpose, is to track the overall intensity drop of a specific bulb to determin its usefull life for some one who doesent want to drop the change for a PAR meter as a lumen meter can be had for 25 bucks.

I do agree we shouden't be shooting for the minimum light thats why I discourage the use of NO's except for actinic lighting. Some people have sucess with but I see more than don't than do.

as for PAR testing I don't do surface testing at all, (I might start doing some that way also) but my tests have been done through an average of 8" of water and 6" of air combined to give a realistic value not a theoretical black box value.

Steve