Re: Measuring light in tank

[busko at stsci_edu (Ivo Busko)]

Zchryk at aol_com wrote:

>     Hi,
>     I have an uncommon light set-up (diy aluminum canopy with raised 
> flourescent fixtures, n.o. bulbs on ice cap electronic ballast), and I want 
> to quantify the light reaching the plants.
>     Using a photography light meter in a baggie, I took readings through it's 
> white plastic diffusion filter (averages the whole field in front of it), and 
> without (which reads a narrow spot in front of it).  Given, are readings 
> (taken with sensor pointing straight up, at 50 asa setting), and their 
> conversion to lux, according to table in Baensch' Aquarium Atlas V1.
>     w/filter:       @ mid-water depth (7")- 2.8f-1/60sec.=2,400 lux
>                     @ just below surface   - 2.8f-1/125sec.=4,800lux
>     w/o filter:           mid-water           (7")- 5.6f-1/250sec.=38,000lux
>                                  just below surface    -       -same-      
> =38,000lux
>     Have visited George Booths' site where he describes readings with a 
> lux-meter but don't know how that compares.  
>     Can anyone help me evaluate these readings?
>     
>     Thank You Kindly,
>     Zach K

Zach,

I understand you actually submerged the photometer, looking up toward the
ligths. In this case the reading that is meaningful is the diffuse one, with 
the filter on. That measures the actual ligth energy per surface unit area at
the receiving spot. You can directly compare it with actual ligth energy
required by plants (in lux).

- Ivo Busko
  Baltimore, MD

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