Beamswork Da Fspec 48"

Dave A

New Member
Aug 25, 2019
I have a 75 gallon planted tank. It has a footprint of 48" x 18". The beamswork da fspec 48" is 3.5" from the top of the water. The water is 18.5" deep. I have a Seneye meter which gives me PAR, PUR%, and a graph of the light reading covering 400-700nm. This unit was reviewed by some reef people and I feel good about the quality.

So here is my question. I am getting PAR reading with the tank full of water and planted along the lines of:

Directly under the light a few inches underwater:

At the front glass at the gravel line:


So my question is this. Do I assume the PAR readings are what shows on the meter or should I be taking that PAR number and multiplying it by the PUR percentage to get the true PAR reading that the plants can use?

The reason I am wondering is when I look at the 400-700 graph I see a lot falling in the middle...

Would you call this LOW, MEDIUM, or (obviously not) HIGH LIGHT

I keep coming back to a post about Amano tanks having 50 PAR at the front edge gravel line and I just wonder.




Aug 23, 2018
The readings you see are complete and you have no need to do anything more with them. Plants primarily utilize light in the blue and red wavelengths. So, lights designed specifically for aquarium plants will place emphasis in these regions. The graph on the left is the PUR output (Photosynthetic USABLE Radiation), not total intensity, which is the PAR (Photosynthetic ACTIVE Radiation). You can think of the color bands as the ideal maximum PUR reading of 100% and the black line on the graph is your lights' PUR performance which, by the way, is a good light. You won't get much higher than 62% PUR with current lighting technology.

Although it is debatable, I consider light categories to be as follows:

High CO2 (30-40ppm) substrate readings
Low Light: 30-50 PAR
Med Light: 50-80 PAR
High Light: >80PAR

This puts your light firmly in the medium category, according to my interpretations. Others could reasonably argue that you are in the lower end of high light. This is due to your path length being 18.5". In a shorter tank, the PAR at the substrate would be higher, making it a high light tank.
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