Peer Review Request: Watts Per Gallon LED

[Ryan - Serious Reefs]

I've been experimenting with light tuning methods that don't rely on a $500 PAR meter. One approach involves using a $30 watt meter instead. While there's skepticism, we're seeing promising results, particularly from a 'Rule of Thumb' standpoint. Finding a cost-effective way for new reefers to adjust their lighting could be a significant advancement.

In this SRLab's (link) we found 1 watt of LED's per gallon was a good rule of thumb for LPS.
In this SRLabs (Link) we found 2.75 watts per gallon was a good rule of thumb right for SPS.
Here Is a (link) so R2R members can watch those videos for free

Now we need that data "Peer Reviewed" by you. If you own a watt meter, controller that measures watts, or light that tells you real time watts used, share how many watts of LEDs you are running per gallon of display and the type of corals you keep. Bonus points if you know the PAR as well.

If a vast majority of you find similar results, together we learned something new and we can share it with the rest of the hobby. I'll consolidate the results in a future video :)

 

[KrisReef]

Bumping for a larger audience!

This is an interesting idea, watt you got going here. Thanks for the free link.

 

[oreo54]

I've been experimenting with light tuning methods that don't rely on a $500 PAR meter. One approach involves using a $30 watt meter instead. While there's skepticism, we're seeing promising results, particularly from a 'Rule of Thumb' standpoint. Finding a cost-effective way for new reefers to adjust their lighting could be a significant advancement.

In this SRLab's (link) we found 1 watt of LED's per gallon was a good rule of thumb for LPS.
In this SRLabs (Link) we found 2.75 watts per gallon was a good rule of thumb right for SPS.
Here Is a (link) so R2R members can watch those videos for free

Now we need that data "Peer Reviewed" by you. If you own a watt meter, controller that measures watts, or light that tells you real time watts used, share how many watts of LEDs you are running per gallon of display and the type of corals you keep. Bonus points if you know the PAR as well.

If a vast majority of you find similar results, together we learned something new and we can share it with the rest of the hobby. I'll consolidate the results in a future video :)

Like the old wpg rule using t12's it breaks down with "non- standard" tanks like very shallow or very deep.

Also matters on the angle of delivery.
This complicates things in the sw world.

Danoplus and VBR Aqua par meters are under $150....

Anyways... Always interesting. I didn't check out the vid yet sooo my opening statement may be off ...

Btw even Tuillio had a positive statement on wpg.

Oh and don't forget the 1w of led = 2w of t5 rule..

 

[Ryan - Serious Reefs]

Like the old wpg rule using t12's it breaks down with "non- standard" tanks like very shallow or very deep.

Also matters on the angle of delivery.
This complicates things in the sw world.

Danoplus and VBR Aqua par meters are under $150....

Anyways... Always interesting. I didn't check out the vid yet sooo my opening statement may be off ...

Btw even Tuillio had a positive statement on wpg.

Currently, many new and even intermediate reefers rely on trial and error, simply flipping switches and guessing based on what looks good to the eye . So, the standard for improvement is pretty low :)

Initially, I wondered if achieving something 'close enough' for 80% of reefers would be a significant step forward. However, after testing and receiving feedback from peers who have applied this 'rule of thumb' to their tanks, it appears it might be more beneficial than I originally thought.

If between here and a hand full of other locations I could get a hundred or so other data points I think we would be able to materially confirm, adjust or move on :)

 

[Vivid Creative Aquatics Verified Sponsor]

I've been watching that series - (I'm a member) and I have enjoyed it. But My tank seems to be somewhat of an anomy - it sits a little outside of your initial findings.

Our office tank, which is a SPS dominate mixed reef, runs a single Neptune SKY, and has since the beginning, which was dry rock, and small frags. The tank is a 134-gallon cube with the dimensions of 36x36x24 cube

I believe the SKY is around 200 watts and the Apex shows that it is peaking at around 193 watts during the day

That puts the tank at around ~1.4 watts per gallon

the tank grown pretty much any SPS coral I've thrown in there and of coarse any LPS an softies.

Here is the power graph on the SKY from the Apex unit, and the light schedule.

and, here are some refence pics of the tank, that i just shot a few minutes ago. The mounting height on the single light is about 14in off the water.


I did a par map on it when we first set it up, but have since lost it. if I remember right, it peaked at around 225-250 at the top, and was very low near the bottom corners - not typically what you would expect to be high enough for these sorts of results,.

 

[rtparty]

According to MyAI, on my 25g AIO (I assume 20-22g in display) I am using 37w between my 2 Grows and 1 Glow. Close to 1.7w per gallon and this gets me SPS levels but on the lower end. I believe the top of my rocks are around 225-250 PAR. Most of these frags were in 250 PAR for a few months and were growing quickly

 

[Ryan - Serious Reefs]

I've been watching that series - (I'm a member) and I have enjoyed it. But My tank seems to be somewhat of an anomy - it sits a little outside of your initial findings.

Our office tank, which is a SPS dominate mixed reef, runs a single Neptune SKY, and has since the beginning, which was dry rock, and small frags. The tank is a 134-gallon cube with the dimensions of 36x36x24 cube

I believe the SKY is around 200 watts and the Apex shows that it is peaking at around 193 watts during the day

That puts the tank at around ~1.4 watts per gallon

the tank grown pretty much any SPS coral I've thrown in there and of coarse any LPS an softies.

Here is the power graph on the SKY from the Apex unit, and the light schedule.

and, here are some refence pics of the tank, that i just shot a few minutes ago. The mounting height on the single light is about 14in off the water.


I did a par map on it when we first set it up, but have since lost it. if I remember right, it peaked at around 225-250 at the top, and was very low near the bottom corners - not typically what you would expect to be high enough for these sorts of results,.

Glads you enjoyed it :)

I think your results highlight where exploration really begins. While this might fall outside of established findings, it’s probably not as far off as it seems—potentially a case where rules of thumb and human intuition align to produce real-world results.

1. There’s some ambiguity in how I asked the original question: were we talking about watts per gallon (w/g) to get most of the tank into the 200–350 PAR zone, or w/g for SPS specifically? Your tank is a great example where peak PAR sits at the lower end of that range but still supports thriving SPS.
2. That said, if your peak PAR is 225–250 at the center, then the bottom and edges are likely lower than that—which covers the majority of the tank volume. From the photos, this seems consistent: SPS growth is strongest in the center, where PAR is highest. I think this illustrates why a mixed reef tank will likely fall somewhere between 1 w/g and 2.75 w/g, depending on how much of the tank you want within the 200–350 PAR range.
3. A 36" x 36" footprint lit by a single module is definitely an outlier, and likely works due to several factors—not least that most of the light is directed into the tank rather than spilling into the room. But it's also important to consider how much tank volume exists within the outer 6" ring. That zone has significantly lower PAR, yet represents roughly half of the physical space (gallons) and will require some initiative thought when applying any 'rule of thumb.'

Question: If your goal were a pure SPS tank and you added another light module—or some fill lighting—to raise most of the tank into the 200–350 PAR range, how far would you be from the 2.75 w/g mark?

 

[Ryan - Serious Reefs]

According to MyAI, on my 25g AIO (I assume 20-22g in display) I am using 37w between my 2 Grows and 1 Glow. Close to 1.7w per gallon and this gets me SPS levels but on the lower end. I believe the top of my rocks are around 225-250 PAR. Most of these frags were in 250 PAR for a few months and were growing quickly

Yeah, we also found that the AI Blades and Edges using similar lenses were anomalously efficient. I suspect the Philips CoralCare, which pioneered that type of lens design, would show similar performance.

 

[spsick]

You’re dead on. I think with the majority of fixtures now shifting to wider coverage (finally, what T5 has had for years) I think a watts per gallon range will be good enough that folks don’t cook or starve corals. At least this gets people to a “lights aren’t my problem” stage.

Outlier fixtures excluded, like a Reefi or Radion with the narrower lenses installed.

 

[Reefer Matt]

I estimated 4.5 watts per gallon (70% intensity Kessil, 100% Reefbrite) peak on this 75 gallon sps tank. Four Kessil a360x tuna blue lights on a Reefbrite xho fixture (2 xho total). Par is 300 up top, 225 in middle, and 150 on bottom. Blanket coverage, no big hotspots. I’ll get a watt meter to confirm.
(Those are shades, not reflectors)

 

[Ryan - Serious Reefs]

I estimated 4.5 watts per gallon (70% intensity Kessil, 100% Reefbrite) peak on this 75 gallon sps tank. Four Kessil a360x tuna blue lights on a Reefbrite xho fixture (2 xho total). Par is 300 up top, 225 in middle, and 150 on bottom. Blanket coverage, no big hotspots. I’ll get a watt meter to confirm.
(Those are shades, not reflectors)

Will be interesting to see of the watt meter matches your expectations but I suspect it will. Before starting this Ryan Thompson ( @rtparty ) suggested I go find out the PAR per watt (efficiency) for the dozens of lights we tested in this BRStv episode called distribution of reef tank lighting. The video had the 108 point PAR measurements and we know the watts but I never thought to do an efficiency calculation of how much par for the watts consumed before.

We talk about it in the first Watt Meter vs Par Meter Video but below you can see how much more PAR you get per watt from some lights. Notable is the Kessils and XHO's had some of the lowest total PAR per watt so I would not be surprised if your set up was a bit higher than the typical 2.75 w/g.

When you look at this you will see that there is a wide range of efficiencies and that would indicate that a w/g ratio won't work but if you exclude the extreme high and low performers it isn't grossly different and that is what we saw when we tested the lights for this series. This is where the rule of thumb coupled with some available info to make educated guesses should get those without a PAR meter a lot closer than "pure guess" :)

*note the watts were not measured at the wall to make this chart. I just looked up the manufactures specs as best I could. Performance could have changed since March 2023 as well

 

[Reefer Matt]

Will be interesting to see of the watt meter matches your expectations but I suspect it will. Before starting this Ryan Thompson ( @rtparty ) suggested I go find out the PAR per watt (efficiency) for the dozens of lights we tested in this BRStv episode called distribution of reef tank lighting. The video had the 108 point PAR measurements and we know the watts but I never thought to do an efficiency calculation of how much par for the watts consumed before.

We talk about it in the first Watt Meter vs Par Meter Video but below you can see how much more PAR you get per watt from some lights. Notable is the Kessils and XHO's had some of the lowest total PAR per watt so I would not be surprised if your set up was a bit higher than the typical 2.75 w/g.

When you look at this you will see that there is a wide range of efficiencies and that would indicate that a w/g ratio won't work but if you exclude the extreme high and low performers it isn't grossly different and that is what we saw when we tested the lights for this series. This is where the rule of thumb coupled with some available info to make educated guesses should get those without a PAR meter a lot closer than "pure guess" :)

*note the watts were not measured at the wall to make this chart. I just looked up the manufactures specs as best I could. Performance could have changed since March 2023 as well

Wow, that’s a lot of good info! Yeah, I knew going into it that the Kessils weren’t very efficient in par/spread. But after seeing them on fellow Reefers’ tanks and watching your vids on them, I decided to try them out. And five years later (when I switched to Kessil), I’m still happy with them. I’ll update this for sure when I get the watt meter. Thanks!

 

[Doctor Derp]

This is precisely how we estimate lighting requirements for "medical" indoor grow facilities. Watts of light per square foot. We know roughly how efficient the diodes are, so a mathematical estimate is easily reached.

Since the sweep of legalization in the last decade or two, there has been a lot of money sunk into horticultural lighting. We're basically doing the same thing, just with a different spectrum. Most modern LED grow lights are of the panel variety. Spread diodes for an evenly distributed blanket of photons.

The tight puck style of light has gone the way of the dinosaurs.

 

[Vivid Creative Aquatics Verified Sponsor]

Glads you enjoyed it :)

I think your results highlight where exploration really begins. While this might fall outside of established findings, it’s probably not as far off as it seems—potentially a case where rules of thumb and human intuition align to produce real-world results.

1. There’s some ambiguity in how I asked the original question: were we talking about watts per gallon (w/g) to get most of the tank into the 200–350 PAR zone, or w/g for SPS specifically? Your tank is a great example where peak PAR sits at the lower end of that range but still supports thriving SPS.
2. That said, if your peak PAR is 225–250 at the center, then the bottom and edges are likely lower than that—which covers the majority of the tank volume. From the photos, this seems consistent: SPS growth is strongest in the center, where PAR is

Yes - much lower. I don't remember exactly how much lower but I do remember well below 100 par

but the odd thing is i can still grow SPS corals in these zones - the main limiting factor now is shading, as opposed to par

Here's one example. its in the front corner, about 3 to 4 inches off the sanded . Just abo as far from the light as you can get. These are not practically finicky coral to begin with but they are growing in a zone where the light shouldn't' be enough.

Here another - this is in the back corner just a few inches off the sand bed. In this case the blue/green SPS was overtaken by the chalice. But before it was, it was growing like a weed. This battler plays out about ever 8 months. I cut the chalice back - trim he SPS, the SPS grows out, and the chalice takes it over.

1. highest. I think this illustrates why a mixed reef tank will likely fall somewhere between 1 w/g and 2.75 w/g, depending on how much of the tank you want within the 200–350 PAR range.

In general I would agree with this - but in my case, it seems the main limiting factor is shading.

1. A 36" x 36" footprint lit by a single module is definitely an outlier, and likely works due to several factors—not least that most of the light is directed into the tank rather than spilling into the room.

I agree with this to - you did a video a while back at BRS regarding how much light bounced off the glass, when light its it at the right angle. i don't remember that angle, but i did have that in mind when I was deciding how high to mount the single SKY light.

My thought process was if its at the right height, the light will hit the glass at the correct angle, and thus direct more of it back into the tank.

1. But it's also important to consider how much tank volume exists within the outer 6" ring. That zone has significantly lower PAR, yet represents roughly half of the physical space (gallons) and will require some initiative thought when applying any 'rule of thumb.'

Originally my plan was only LPS and softie in these zones. But it didn't work out that wat - LOL

Question: If your goal were a pure SPS tank and you added another light module—or some fill lighting—to raise most of the tank into the 200–350 PAR range, how far would you be from the 2.75 w/g mark?

I like the SKY light since I have always been partial to the more broad spectrum, natural looking light (Windex blue doesn't do it for me), so i had considered 4 SKY lights - to fully cover the footprint of the tank

If i had done that - then I would be at near 5 to 6watts per gallon at 90% to 100% power. It would have been very bright. I likely would have run that at only 50% max.


But - with the shading issues i do need to add some supplemental light. I am considering a few options but one of them is a pair of either the 21in or 32in AI Blade Grow lights..

I think these are in the 40 to 60 watt range. Estimating on the low end at 40-watts, that would be
40 + 40 + 200 = 280 / 134 = 2.08 watts per gallon

 

[areefer01]

I've been watching that series - (I'm a member) and I have enjoyed it. But My tank seems to be somewhat of an anomy - it sits a little outside of your initial findings.

Our office tank, which is a SPS dominate mixed reef, runs a single Neptune SKY, and has since the beginning, which was dry rock, and small frags. The tank is a 134-gallon cube with the dimensions of 36x36x24 cube

I believe the SKY is around 200 watts and the Apex shows that it is peaking at around 193 watts during the day

That puts the tank at around ~1.4 watts per gallon

the tank grown pretty much any SPS coral I've thrown in there and of coarse any LPS an softies.

Here is the power graph on the SKY from the Apex unit, and the light schedule.

and, here are some refence pics of the tank, that i just shot a few minutes ago. The mounting height on the single light is about 14in off the water.


I did a par map on it when we first set it up, but have since lost it. if I remember right, it peaked at around 225-250 at the top, and was very low near the bottom corners - not typically what you would expect to be high enough for these sorts of results,.

You are not alone. I have been running a pair of SKY's since the NSI testing started over my 210 gallon display. I do not run my lights at 100% but rather 85% and use a parabola light schedule. I believe there is a thing called too much light after reading a few papers from Mr. Dana Riddle.

How I derived my light schedule. Neptune made it silly easy to take PAR measurements across the various pre-built and custom light settings plus intensity. As I run the parabola light schedule I picked an intensity to start at then ramped it up a bit each hour to 100% and repeated that to when I turn the lights off. This is what I have been using (Coral Growth) since I installed them.

My display as of April, 2025. Mixed reef. I have a couple large SPS colonies that are shading the reef such as my 23" BC Efflo 2.0.

 

[Hooz]

I have a JBJ 65 AiO tank with a pair of Hydra 26HDs (Luxdium LED and lens upgrades) mounted 10" above the water and 10" in from each end. It holds exactly 52 gallons of water.

I used an Apogee 510 to adjust the PAR for softies and LPS. Aimed for about 85 PAR on the sand and the top of the rocks sits in the mid 130's.

I am also a SR member and, after watching the SR Labs video, I fired up myAI and it showed that (at peak), I was running 26 watts per light, or a total of 52 watts for the 52 gallons.

ETA: I have several other nano tanks that fall outside of "normal" for one reason or another. Some with the lights mounted higher than would be "optimal", or with inhabitants that fall outside of the LPS or SPS boxes (mushrooms, anemones, etc).The watts/gallon ratio doesn't match up well to what you're testing here, but I wouldn't expect them to. I'm curious to see where things end up on my 12g SPS tank with 2 Primes, but I'm currently running lights off while the tank matures and haven't even tinkered with the lights yet.

 

[rtparty]

I know this about LEDs but I PAR mapped my new tank that is using MH/T5s

The T5s are 39w bulbs but the Giesemann ballasts don’t run them at 39w. Once warmed up it only pulls 125-130w for all 4 bulbs. That’s roughly 1.25w per gallon and I get 70-100 PAR at the top of the rock to the sand bed. The fixture is pretty high over the water. These T5s are being replaced with Blades soon.

I don’t have the halides on a power bar with watt metering but I believe an M80 ballast and Radium bulb runs at like 280-300w. So all in I’m over 6w per gallon. I also see 350-400 PAR from top of rock to sand. In the middle of the 2 rocks, I’m getting 450+ PAR

 

[gcarroll]

I’m convinced there’s a lot of there “there!” I’ll admit, I wasn’t so sure how valid it would be, and then I went back to figure out my numbers.

I run my 5 Radion blues at 102w each. And 2 80w blades at 100%

Radion
102w x 5
80w x 2
Total 670w

PAR on this tank is around 600 - 500 at the upper corals and 200-300 at the bottom.


Tank is 250g
So that is 2.68w/gallon

 

[Troylee]

750 watts with two 63” Meridans at 100% par is 700ish at the top of the rocks and 350 in the sand over a 300gal display. So 2.5w per gallon with a stuffed sps tank and pretty even coverage. No other supplemental lighting.

 

[Drewe]

Hey Ryan -

After watching the videos on YouTube when they came out I actually did check one of my tanks (the one with the apex, don't have a standalone watt meter.)

This particular tank is 36x24x20, so 72 gallons give or take and is lit by two 150 Nicrew Gen2s.

During the photo period I'm using 155 watts which translates to 2.15 watts per gallon. I believe I have this set at 75% blue and violet and 12% whites. This tank is mixed with euphylia, acans, zoanthids, a few tried and true acros and lots of montipora, stylos etc.

8" off the water, at 8 inches below the water level during the photo period I'm getting 250-275par and 120-150 on the sandbed per par meter. Falls right in line with where I'd expect it to be in a mixed tank at this wattage per your videos.