PPFD/ PAR conversion factor

[DenverDave]

Hi,

Sanjay's sight repots PPFD for various bulbs in various situations.

For my Radium 20K 150W bulb on an electronic ballast and shielded, Sanjay gives a PPFD of 36.

However, I've read through some threads on RC and it seems that most acros' target range is 200-400 PAR (whatever those units are).

Does anyone know of some sort of conversion factor that I could use? Sanjay said (I think) that PAR is a function of depth, and his PPFD readings were all made at 18 inches below the light ("All measurements are made at 18” from the centerline of the lamp to the top of the sensor dome.") However, I don't know how much of this depth is air above the water.

I'm just trying to get a feel for what a 150W Radium produces in the top 8 inches of the water directly below the bulb with the bulb itself about 4-5 inches off of the water surface without using a measuring device- anyone have any ideas?

AKA, am I even close to the 200-400 range that is supposedly sufficient for photosynthetic acros?

Thanks!
Dave

 

[Entropy]

http://reefkeeping.com/issues/2006-04/sj/index.php

Everything you never wanted to know about Par.

 

[DarG]

Sanjays testing was done with no reflector and no water if we are talking about his page with all the different bulb measurements. It is a wealth of info but it was done to make relative comparisons of all the different lamps in terms of color and output. It doesnt take into consideration the reflector or the water. Just a raw comparison of the different bulbs.

To put it simply, the par of the radium will be far higher than his raw measurement of 36 ppfd with a reflector and 8" below the lamp in the tank.

 

[DenverDave]

Hello again, DarG

Are the units the same? If so, to get 36 ppfd into the 200-400 range for light loving acros, then my par at 8 inches below the water would have to be a 10-fold increase from Sanjay's measurements.

Is this possible?

Dave

 

[DarG]

<a href=showthread.php?s=&postid=15051867#post15051867 target=_blank>Originally posted</a> by DenverDave
Hello again, DarG

Are the units the same? If so, to get 36 ppfd into the 200-400 range for light loving acros, then my par at 8 inches below the water would have to be a 10-fold increase from Sanjay's measurements.

Is this possible?

Dave

Hi Dave. Go to Sanjays site and look at his articles section. Find the reflector tests. There are several of them using several different lamp types, brands, wattages. They will give you a much better idea than the raw data comparing the bulbs alone. Well worth the browse.

 

[DenverDave]

Thanks for the information, guys.