When you are just comparing two or more setups there are several ways to do it without the PAR meter. It is when you want to compare to some standard or compare to someone's tank in another state that you need a PAR meter. Then, of course, in-the-water measurements would be preferable too.

I have been thinking more about the question, does the light intensity drop off differently for long linear bulbs than for short "blob" bulbs. I downloaded some log log "paper" from the internet and replotted some of the data I took - the center line of the tank from the substrate level up to near the plane of the bulbs. Here is what it looks like:



I think it is clear that there is a different drop off rate for the two fixtures I tested. And, it appears that the almost linear AH Supply PC bulbs appear to lose intensity inversely approximately proportional to the distance from the bulb. But, the CFL screw-in bulbs seem to lose intensity approximately proportional to the inverse square of the distance. As you get close to the plane of the bulbs, the relationship seems to break down, and that is explainable because the "linear source" is less and less a linear source as you get close to it. The same is true of the "blob" source. I'm sure these relationships break down at the ends of the tanks too for obvious reasons.

This isn't proof of anything, but it does suggest to me that one reason for the effectiveness of T5 bulbs is that they are close to true linear light sources. And, to me it suggests an explanation for why people can successfully use what appear to be way over powered MH bulbs - they are suspended further above the tank, and their very high light intensity drops to a reasonable level as you do deeper into the tank. It makes me also think that the ability of MH fixtures to "penetrate" deep tanks is largely because they are so bright to start with.

I think maybe I have now squeezed out all that I can from the data I took.

Comparison can be made using a Lux meter to get performance results between someone's tank in another state. When comparing light performance the in-the-water measurement might not be the way to go to get meaningful data concerning the lights being used as the water clarity would have a significant effect.

If using a light meter for comparison results how do you calibrate the meter?

Regarding the mylar being tested, was there a reflectivity rating?
Some mylar is advertised as having a 98% reflectivity and other mylar does not advertise a rating.

I got the mylar from another aquatic plant keeper, left over from a project he did, so I don't know what it was advertised to be. It is 3 mil thick, and doesn't transmit light through it, as a lot of mylar does, plus it is aluminized on both sides. All of that tells me it has high reflectance.

I have often been told on various forums, by experienced people, that mylar is not nearly as good a reflector as it seems to be. Being a skeptic I chose not to believe that. The stuff just looks so good! Compared to aluminum foil it looks like a much more efficient reflector, but that is a trick our eyes play on us. We judge a reflector by how true the reflection is, by how much it looks like a great mirror to shave by. And, that has nothing at all to do with how good the reflectance is.

I would like to say from now on I will believe what experienced people tell me.........but I'm sure I won't. Incidentally, experienced people by the dozens, also tell me that white paint is a great reflector, but with my superior knowledge I laughed that off too. Wrong again. But, I also assured a lot of people that Senator Obama could never possibly win the Democratic Presidential nomination. And, back in 1989 I assured a lot of friends that the San Francisco Giants would beat the Oakland A's in the world series. To my credit I did predict that Sacramento summers would see little or no rain.

Hi, I've got a LX-1020B & an LX-1330B lux meters that I've used for photography (outdoor & indoor) but i was wondering if this have a use in aquarium either in light fixtures on the aquarium or in aquarium photography. I've reading about this light meters for aquariums and it got me more confused i just want to know if these type of lux/light meters can be use in aquariums in any way.

link for 1020B & 1330B light meters:
DIGITAL LIGHT METER 100,000 LUX LCD LAB PHOTO CAMERA - eBay (item 330242481267 end time Jun-14-08 00:40:47 PDT)
NEW DIGITAL LIGHT LEVEL METER 200,000 LUX PHOTO CAMERA - eBay (item 330243179304 end time Jun-16-08 15:03:15 PDT)

any information to enlighten me is very much appreciated. many thanks in advance.

Thanks for posting this, it has been an interesting read so far.