Lighting, PAR and DLI

[pascal32]

Out of curiosity I started reading up on reef lighting in an attempt to somewhat quantify what proper lighting is.

the hope is to:

(1) ensure my reef is properly lit
(2) try to create a similar environment in my frag tank as the display for ease of moving frags
(3) try to make the LPS frag tank lit the same as the bottom of my display

To help with this process I borrowed a PAR meter. I will concede the PAR meter is of unknown age, and likely is in need of calibration. Even if it is out of calibration it still serves as a consistent measurement for synchronization of the frag tanks to the display tank.

Par readings (dusk dawn/daylight)

Display - 120 Gallon 48", 24" tall, 8xT5 using two fixtures with pressed individual reflectors. Note that the high point is that of my rock stack which is about 9" down

high point: 158/270
Mid Point: 110/189
Sand: 84/180

Frag Tank

(left)
top rack: 60/180
bottom rack: 51/144

(right) - yes, the right side reads higher
top rack: 80/237
bottom rack: 71/183 (right tank lower level is 2" down from left)

I took these numbers and ran them against my light cycle of:
8-11 dusk/dawn
11-5 daylight
5-9 dusk/dawn

this gives me a DLI (Daily Light Integral) as follows:

display:
high point: 9.81
Mid Point: 6.85
Sand: 6

(left)
top rack: 5.4
bottom rack: 4.4

(right) - yes, the right side reads higher
top rack: 7.14
bottom rack: 5.74 (right tank lower level is 2" down from left)

According to advanced aquarist a natural reef has 16-30 DLI depending on season.

It starts to get even more interesting. Advanced Aquarist believes that photosynthesis saturates at 200-400 PAR for most corals.

So taking this in to some extent you can extend the photo period to provide enough DLI - within limits. You can read the article which contains a description of the photosynthesis cycle and at what point the cycle is disrupted.

There were some interesting observations:
* tilting the meter yields dramatically different results
* the frag tanks don't have the same amount of light (left by the labels and fan are lower)
* in the frag tanks the centers are higher than the sides (likely due to the two glass walls blocking light between the tanks (one covered in algae)

I'm hoping for some feedback on DLI and other folks experiences. I have two unused T5s on the Display and the Frag tank, so i can increase lighting - the flip side is that frag tank is doing great. The display shows some sign of lack of lighting with the SPS which are not up on the tipy-top

The following links were the most useful:
http://www.advancedaquarist.com/2009/5/aafeature
http://www.advancedaquarist.com/2006/1/lines/view?searchterm=par
http://reefcentral.com/forums/showthread.php?s=&postid=14976874

 

[dreaminmel]

Bump back to page 1 for you.

I have no knowledge of DLI but my thoughts after reading are this... If your sps are doing great in the frag tank but showing lack of light lower in the display, I'd personally be tempted to leave the frag lighting alone and try an increase over the display of some sort. If I remember right everything is plumbed together so there wouldn't be any difference in water quality to justify the signs. It's curious that the old meter showed higher #'s for the display though and that's where lower sps don't look right to you. I know that some sps require higher lighting than others. I tend to take visual signs more to heart than technology so if I was in the situation I'd be tempted to try moving up coral that don't like being low and if that didn't help, try a lighting increase.

Hopefully some others can give ya some feedback on the DLI, etc though. G'luck.

 

[der_wille_zur_macht]

I agree with Mel, observational results matter more to me than numbers. The "inconsistencies" between your two frag tanks (which iirc are lit identically?) are interesting, as is the amount the reading changes with small changes in position or angle as you observed. I don't think these factors should discourage people from trying to look at numbers, but IMHO the numbers should be taken with a grain of salt.

The display shows some sign of lack of lighting with the SPS which are not up on the tipy-top

What exactly are your observations? Poor coloration? Poor growth? Both? What are the flow differences between the frag tanks and display tank? Do you have frags of those exact same corals in the frag tanks or elsewhere in the DT?

 

[Gravesj1s]

I'm not sure either.

I believe a par meter should be mounted to get more consistent and accurate results.Most people I've seen use a grid pattern and a plastic stick of sort attached to the meter for best results.

 

[oneradtek202]

this would be a great question for melev!

 

[pascal32]

Thanks for the responses. The display and frag both look great. There are a few pieces in the display which are lacking a bit in color, most notably the green Same issue with the birdsnest in the frag tank. The tricolor Bali as at the top and looks absolutely fantastic!

I'm wondering if PUR has something to do with what appear to be somewhat conflicting results. If I understand correctly, 90% or so of photosynthesis occur from 400nm to 500nm, and a PAR meter reads from 400-700 which means I could have a better spectrum in the frag tank.

I need to pull up some spectrums on the bulbs!

For now I'm going to add some light to the display and see if color comes in a bit better. I'll start slowly with 30 minutes additional per day till I'm up to 4 hours and cut the overall duration back an hour to 12 hours.

Just neat to read up!