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Re: Light Meters

"Wayne Jones" <waj at mnsi_net> wrote:

> I think you could also obtain different readings for the same object
> depending on the angle you view it at through the glass. Also the
> orientation of the object seems to me should matter as well. Wouldn't a
> vertical flat object collect less light than a than a horizontal object if
> there was more light entering the tank at a high angle. I find it hard to
> believe that changing the orientation of something flat would not change the
> reading that you get. Changing the orientation of a sphere though obviously
> wouldn't do anything.

That's right, the readings should change with object orientation.  At least 
in my saucer measurements in the planted tank, I had to lay the saucer at 
different angles anyway due to stones, driftwood, and to avoid crunching 
plants. But I attempted to lay it as close to the horizontal as I could,
since plants are supposed to orient their leaf surfaces about in the same
way. Near the front glass I measured it both horizontally and at a angle. 
The readings were hard to tell apart given the camera's limitations, but 
they seemed to be a bit higher in the horizontal position. As for the angle 
of view thru the glass, I didn't see any measurable effect. Again, I tried
to keep the camera consistently at a rigth angle with the glass.

IMO, all these effects, including the extra low-angle ligth you suggest 
(and I agree) should exist with a white reflector hood, are second-order 
effects given the precision we can get from such measurements. The main 
point in using the cheapo technique is that it costs nothing, and it
apparently can provide me with the data I need in order to design a light
canopy. Of course I would feel more confident if working with a properly 
designed underwater meter, but that wouldn't be as fun !

- Ivo Busko
  Baltimore, MD