No offense taken rishma. And like you said just a difference of opinion. If you can agree to disagree, I feel an open air test will not tell you much about illuminating your tank as each reflector drives light into the water differently. I actually tested a parabolic relfector yesterday and was getting 100-150 on the bottom under a 400w bulb along with 2 -250's next to it and 3-6ft VHO's. Clearly the reflector did not drive light deep into the tank. Every tank I had tested so far has raised an eyebrow of the tank owner when they actually see what their reflectors are actually putting out or their VHO's or magnetic ballasts for some reason. Every tank other than a LumenBright tank I should say
Again I will not argue that a grid is more repeatable. Just to note, when we rechecked certain numbers, it was interesting that the second set was very close to the first, maybe 1 or 2 PAR off. So at least on the same tank the numbers are repeatable. Another thing to note, if you look at Deuce's, Kurts Reef's, Mike L.'s(Acropora Nut's), and my tank, we all have 400w 12K Reeflux and are pretty much measuring comparable numbers so I believe anyone using this bulb, ballast, reflector combination can get a pretty good idea from the pictures already posted. Again, an open air test will never tell "you" how the light will be driven into "your" tank. Everything changes when the surface of the water is broken and some reflectors drive light through the water better than others. It does not matter how far a distance you place the bulb from a grid, without water you will never know how that light will penetrate "your" water.
The last few weeks have been very interesting owning a Apogee meter. I have opened a lot of eyes as to realizing their thoughts on how their lighting systems were performing was way off. Justin had measured his 30g long T5 tank and noticed his LUX meter was showing numbers almost in half of what the PAR meter was showing. Following the results from the LUX meter he decided to lower his T5 fixture because he did not think he had enough light. He was very surprised as was I with the "actual" results and realized his fixture did not need to be so low.
I suggest to anyone if you have the means to purchase one(an Apogee Quantum Meter) for yourself or borrow one from your local reef club or suggest that they purchase one to be shared amongst club members. I don't suggest relying on everyone else's data to determine what could be a detrimental factor in the life of your inhabitants in your reef tank. Many of our tanks costs thousands of dollars and I feel a couple hundred dollars is a drop in the bucket to have some certainty in regards to your lighting. Honestly, it has been the best investment I have made in reefkeeping in a long time and I have gotten a lot more use of it than I thought I would, including fellow reefkeepers that are no longer in the dark about their tanks
