Will You Explain How to Calculate DLI?

[chaoticreefer]

Hi Dana,
I have watched your interview with Terrance (Neptune Systems) on the Sky last night. Will you please explain how exactly do you calculate DLI on our tanks? Is it just something as simple as PAR divide by time span? With my luck, that sounds too simple.

Also...will the Sky, that you know of, include this calculation in it's software?

Thanks Dana, I am always looking forward in learning from you.

Bill

 

[Jekyl]

@Dana Riddle

 

[areefer01]

These may help you. If you have time they are worth the read. I have a feeling this topic is going to be coming up a lot because some people are going to say Neptune is changing the rules. There are no rules changing and this subject has been discussed for a number of years. There is more to successful reefs than a PAR number. It is just gaining traction now that new lighting kits are coming out.

Edit: I realize that maybe you wanted the actual formula. Per the first link it reads (note - copy/paste):

The formula for DLI is simple. It is Photosynthetically Active Radiation (PAR, reported as micromole per square meter per second, or molm²sec) times the photoperiod in seconds.

For example, let’s determine the DLI for a coral receiving 250 molm²sec for 12 hours:

250 molm2sec * (12 hours * 60 minutes per hour * 60 seconds per minute, for a total of 43,200 seconds) = 10,800,000 molm² in 12 hours. We can divide the result by 1,000,000 to arrive at usable shorthand of Mol per Day, which is 10.8 Mol per Day.

Another, slightly more complicated, example:

• Actinic lamps delivering 100 molm2sec on at 6 am, off at 8 pm (14 hours). A metal halide lamp delivering an additional 300 molm2sec is on from 11 am to 6 pm (7 hours).
• Actinic lamp DLI = 100 molm2sec * (14 * 60 * 60) = 5.04 Mol per Day.
• Metal halide DLI = 300 molm2sec * (7 * 60 * 60) = 7.56 Mol per Day, for a total DLI of 12.6 Mol per Day.
  https://cdn.reefs.com/blog/wp-content/uploads/2009/05/image002-bf7d8c75a410dff4a414a9ddfae153be.jpg

A Different Look at Lighting: Effects of Prolonged Photoperiod, Spectral Quality, and Light Dosage

Some reef aquaria 'experts' have suggested that we understand all we need to know about lighting of reef aquaria. This article will suggest otherwise.

reefs.com

Imitating Natural Light Quality, Intensity, and Dosage in a Reef Aquarium – Do We Really Want To?

When it comes to reef aquariums, Mother Nature has always been the de facto benchmark aquarists aspire towards. Dana investigates in great detail the quality and quantity of light over natural reefs in order to lay the groundwork to answer the age-old question: what is the best light for...

reefs.com

 

[oreo54]

Hi Dana,
I have watched your interview with Terrance (Neptune Systems) on the Sky last night. Will you please explain how exactly do you calculate DLI on our tanks? Is it just something as simple as PAR divide by time span? With my luck, that sounds too simple.

Also...will the Sky, that you know of, include this calculation in it's software?

Thanks Dana, I am always looking forward in learning from you.

Bill

Start here for steady state lighting... i.e on/off 200 par 10 hours..

Daily Light Integral (DLI) Calculator | Waveform Lighting

With a PPFD input value and total hours of use per day, Daily Light Integral (DLI) values can be calculated using our online calculator.

www.waveformlighting.com

Of course ramping makes it a lot more difficult to calculate it.
0,25,50,100,100,100,100,50,25,0 "par"
Average 55 par over 10 hours.
1.98 dli per calculator.
More points the better.

If you want to not use the calc..

Once you know the average over a 24 hour period you will multiply it by 0.0864 to get the mols/day. This factor is the total number of seconds in a day divided by 1,000,000

550 (using above example) / 24 = 22.91 x .0864 = 1.97

 

[Dana Riddle]

@areefer01 explained DLI well. I calculated DLI for the bottom of my reef, and it is about 7. At the top of the tank, where light intensity is higher, the DLI is about 11. All corals are doing well. I'll post some photos with PAR/DLI numbers in my build thread when things slow down a little.

 

[Dana Riddle]

Hi Dana,
I have watched your interview with Terrance (Neptune Systems) on the Sky last night. Will you please explain how exactly do you calculate DLI on our tanks? Is it just something as simple as PAR divide by time span? With my luck, that sounds too simple.

Also...will the Sky, that you know of, include this calculation in it's software?

Thanks Dana, I am always looking forward in learning from you.

Bill

Hi Bill, Please see responses below - they explain how to calculate DLI well. I calculated DLI in my tank using PAR measurements made with Neptune's PMK (PAR module). See below for details. The SKY software doesn't do that automatically to the best of my knowledge - it would be a good question for those more familiar with writing code for the Apex. If that's not an option, some (perhaps all) of the Apogee Instruments PAR meters will calculate DLI when in the 'log' mode.

 

[areefer01]

Start here for steady state lighting... i.e on/off 200 par 10 hours..

Daily Light Integral (DLI) Calculator | Waveform Lighting

With a PPFD input value and total hours of use per day, Daily Light Integral (DLI) values can be calculated using our online calculator.

www.waveformlighting.com

Of course ramping makes it a lot more difficult to calculate it.
0,25,50,100,100,100,100,50,25,0 "par"
Average 55 par over 10 hours.
1.98 dli per calculator.
More points the better.

If you want to not use the calc..


550 (using above example) / 24 = 22.91 x .0864 = 1.97

With regards to ramp up I think it is fine but just more work. If you own a controller it is of course easier. Using Numbers, or Excel, or Pad of paper write out your schedule (time) and intensity for the desired spectrum. Measure part at each point. Formula is the same so just calculate each. Now you have your numbers to look at the average, 90th, and 95th percentile. You can then look at the numbers and adjust intensity or light duration and let that be your guide.

At least this is how I'm doing it.

 

[oreo54]

Once you know the average over a 24 hour period you will multiply it by 0.0864 to get the mols/day

Too complicated??? LOL
Average daily par anyway you see fit .

Sorry, just having a bit of fun..Call it dli for dummies .

Each spot in the tank will have a slightly or not so slightly different dli.

 

[oreo54]

Daily Light Integral: Measuring Light for Plants

www.apogeeinstruments.com

PAR, Daily Light Integral, and Photoperiod Meters - Daily Light Integral Measurement - Apogee Instruments, Inc.

www.apogeeinstruments.com

Adding the function to apex should be a piece of cake.

 

[areefer01]

Actually with the Neptune mobile app and the SKY light is pretty easy even if using say a Seneye. Once you have the PAR device where you want it you can bring up the app, adjust the intensity, look at the reading, note it down, and then increase to the next schedule intensity. Repeat until done or move to the next pre-defined spectrum. It really is simple. The app's intensity slider is instant so it is quick to navigate through all of your settings. Or use the average as you suggested Oreo.

I've done this for the middle of my display because I had a SPS acro that started to look pale. I believe it was caused by too much light. The lower middle of my display which is 210 gallons (54 x 30 x 30) and tall reads 8.51. My sand bed about 6.

Dana's numbers are more accurate as he has better tools. I'm just using numbers as a reference for my system because the corals as a whole are receiving more surrounding light or coverage. Some responded very well but I do have a few that I've had to move or slowly acclimate.

DLI seems like a good tool regardless of fixture. Have to say I'm a fan.

 

[Fogy]

Is there a way to fool the Seneye into working out of the water? I want to measure PAR around the house for houseplants.

 

[oreo54]

Is there a way to fool the Seneye into working out of the water? I want to measure PAR around the house for houseplants.

I "believe" (from memory) "they" said it works just fine out of water.
Even the flashing red leds (out of water warning) doesn't affect it.

Old apogee sensors immersion factor was very low as a comparison. Like 1.09x

Since you are considering just daylight for the most part, a Lux meter works just fine as well

Convert Lux to PPFD - Online Calculator | Waveform Lighting

Online calculator to convert illuminance (lux) to PPFD (micromoles per second per meter squared).

www.waveformlighting.com

100 Lux = 2.3 "PAR"