Blueacro led

[RedneckReefer68]

I'm a little confused...I have the half star 20k pros. On the web site it listed par at 12" from the light at 1 amp as 380 par. I used my lux meter (15$ red one from Amazon) to measure at the water level with the LEDs hanging 7" above. I got a reading of 57000 directly under and 37000 half way between pucks. Dividing the 57000 with 60 is 950 par at the water level (7"). The top of my rocks is about 6" below the surface. I have no idea what kind of par I'm putting on my acros at that level. It doesn't seem like par would drop 600 points just in 6" of water?

@saltyfilmfolks

Pic of my fixture in actually using 4 pucks now, so the are spaced about 5 " apart. Allot closer than they are in this pic

 

[chipmunkofdoom2]

Why not take the light off the tank and measure 12" below that? It's no good assuming something is wrong, why not pull the light and verify?

Also, it's worth noting that there's going to be some spill from the adjacent puck even if it's a few inches away from the one you're measuring. The PAR figure from the blueAcro site might be assuming that you're running a single puck only.

 

[oreo54]

12" is almost 2x the 7" why would you think you wouldn't get 1/2 the PAR?

Though light from a point light source drops like this:
https://en.wikipedia.org/wiki/Inverse-square_law
2x the distance 1/4 of the light

Pucks aren't exactly point light sources and behave rather linear in "our" distances sooooooooooo 950 @ 7 and 475 @ 14"
would not be out of the range of possibility. 2x distance 1/2 light not 1/4.

Second 60 is a "ballpark" number ..could be 67 ect. ect.. 850 not 950.

Last @ 120 degrees and 7" light cone is 24" if puck centers (actually more like edge diode to edge diode) are not farther than 24" apart they will start to blend.
Measuring at 12" and cone diameter is 41" and def blending together.. though it will give you a better idea of reality..

note that the edges of these cones have way less light than one thinks, w/ a huge percentage at a smaller diameter.

 

[Bpb]

Inverse square law states that when you double the distance from the source, light intensity will be reduced by a factor of 4. Though I’m not sure how tight lenses/optics effect that. Having a reflector will kind of skew that law.

 

[oreo54]

Inverse square law states that when you double the distance from the source, light intensity will be reduced by a factor of 4. Though I’m not sure how tight lenses/optics effect that. Having a reflector will kind of skew that law.

Yes for a point light source and large distances.. Really doesn't apply here .. Range is "more linear"..Though a bit of both..
Just take the data points from 15 and 30..
Once the light gets into the water column reflection and refraction mess w/ it as well..

 

[jda]

To have 750 PAR 9" under the water, mine are at 2600 just under the surface. They fall off pretty fast as they spread.

 

[User1]

Some interesting replies and good information. I have four of the mega star 20k pros over my 30" tall 210 gallon and they are pretty intense. No idea what the par is or would be.

Side question - how much power or what was their intensity if you don't mind me asking if you are using a controller?