Logical Lighting Thought.

[sacramonel]

I was on Liveaquaria today and they post the lighting requirements in watts per gallon. I know this is not how it is measured in the saltwater world and then I began to wonder why not. I can not understand why photosynthesis in coral is any different than the photosynthesis in aquatic plants. If an aquatic plant requires high lighting, then it is given a 4-5 WPG rate. Why can't this be similarly used in reef aquaria?

 

[Lynden]

It can, but a better way is to measure the square footage of your tank, then find the depth and base your lighting on that.

 

[n3ont3tra]

Usually PCs are used in planted tanks, so it's all the same. 40 watts of one power compact is pretty much the same as another 40 watts of power compacts.
But in the marine world, we use PC's, T5's, metal halides, etc. A 40watt PC has nowhere near the intensity of 40watts of metal halides. It also depends on how deep the tank is, and how high the lights are placed over the tank. And what reflectors are used.

 

[sacramonel]

Usually PCs are used in planted tanks, so it's all the same. 40 watts of one power compact is pretty much the same as another 40 watts of power compacts.
But in the marine world, we use PC's, T5's, metal halides, etc. A 40watt PC has nowhere near the intensity of 40watts of metal halides. It also depends on how deep the tank is, and how high the lights are placed over the tank. And what reflectors are used.

If this is the case then how do we determine what intensity lighting is appropriate. Is the benchmark that can be used? For instance 12 inch dept a 150 is used, 18 250 and etc. I ask because the literature I have read only states that the more intense the light the better. If that is the case why stop at 400's, why not 750's or 1000's. I think that a bench mark would make it easier for beginners to determine the optimal lighting spectrum/intensity for their specific aquarium.

 

[n3ont3tra]

If this is the case then how do we determine what intensity lighting is appropriate.

It depends on what kind of corals you want (if any), and how big the tank is.

Is the benchmark that can be used? For instance 12 inch dept a 150 is used, 18 250 and etc.

The depth is just one thing, length and width also matter. Metal halides, for example, only really cover about 24" lengthwise. So if you had a 48" long tank, you would need at least 2 halides or else you'd have a huge shadow.

I ask because the literature I have read only states that the more intense the light the better. If that is the case why stop at 400's, why not 750's or 1000's. I think that a bench mark would make it easier for beginners to determine the optimal lighting spectrum/intensity for their specific aquarium.

Part of the reason is heat. A 1000w metal halide will put out a lot of heat, and you'd have to find a way to keep it cool. The second reason is cost. There's a big diference in the cost of the electric bill of a tank lit with 250 watts and a tank lit with 1000 watts.

There's probably a lot more to what I'm saying, I'm not really an expert. But this is just what I know and it makes sense to me.

 

[sacramonel]

If this is the case then how do we determine what intensity lighting is appropriate.

It depends on what kind of corals you want (if any), and how big the tank is.

Is the benchmark that can be used? For instance 12 inch dept a 150 is used, 18 250 and etc.

The depth is just one thing, length and width also matter. Metal halides, for example, only really cover about 24" lengthwise. So if you had a 48" long tank, you would need at least 2 halides or else you'd have a huge shadow.

I ask because the literature I have read only states that the more intense the light the better. If that is the case why stop at 400's, why not 750's or 1000's. I think that a bench mark would make it easier for beginners to determine the optimal lighting spectrum/intensity for their specific aquarium.

Part of the reason is heat. A 1000w metal halide will put out a lot of heat, and you'd have to find a way to keep it cool. The second reason is cost. There's a big diference in the cost of the electric bill of a tank lit with 250 watts and a tank lit with 1000 watts.

There's probably a lot more to what I'm saying, I'm not really an expert. But this is just what I know and it makes sense to me.

Truthfully, it makes sense to me too. I just get a lot of questions from people asking me to explain to them what a minimum requirement for lighting should be. Its difficult to explain with out some numbers to throw out at them. For example I know a lot of people who use 150mh for an SPS tank and do very well. Then again there are people who use 250's and 400's. I know a lot of us on this forum do not have thousands of dollars to throw at lighting(unlike those on Reefcentral!!) So finding the optimal lighting solution without going overboard is what most of us are trying to find out.

Personally I'm trying to figure out of the two 150MH unit I'm getting is going to be optimal or not. I'm getting it for a song, and can not pass it up.

 

[Musho3210]

and remember, T5 linears are better than T5 PC's in most cases

 

[Lynden]

Agreed. Though with good reflectors, both should be able to support the same life.

 

[SkiFletch]

The true measure of a bulb's effectiveness at providing usable light for corals is not watts or even lumens. The measusure that is useful to marine aquarists is PAR (photosynthetically available radiation) AT the coral. PAR is measured in microeinstiens and is essentially a measure of the amount of light in the wavelengths capable of encouraging photosynthesis.

PAR can be greatly increased via the use of good quality efficient reflectors as Musho has alluded to. The best example is of course T5 and PC lights. T5 lights can have individual reflectors, focusing nearly all the light from every tube down on the corals. PCs however waste a lot of light trying to shine through the bulbs next to them as well as multiple rebounds around the reflector all wasting light. Therefore, a bank of 2 T5s will have nearly twice the PAR of similar wattage to a single PC bulb down on the corals.

Metal Halides and T5's by far have the best reflectors and the best light output. Their PAR/watt ratio are the greatest by far. For years, Halides were really the only way to grow high-PAR requiring corals like acropora, montipora, nems, clams, etc. Within the past 5-10 years however T5s, most notably T5HO have been able to match Halides in terms of PAR delivered to corals. Banks of say 6 or 8 T5s can even offer more PAR than some halide setups, although the power-guzzling 250 and 400watt halides are hard to beat.

All that said the choice between T5HO and Halides is a real tough one nowadays as both put out similar PAR per watt. One thing to remember is that T5HO bulbs will decay faster than halides and of course it requires more physical bulbs to create the same amount of light. This means that bulb replacement can get costly for T5HO sytems. Halides offer their own challenges with large reflectors and lots of heat produced.

Too bad it's not as simple as watts per gallon

 

[Musho3210]

another thing to add with t5 vs mh is mh's are easier to cool since all the heat is concentrated at once spot, if you dissapate the heat in that one spot with a fan or something you are removing a lot of heat. With T5's the heat is spread out all through the lighting tubes which means you need a lot of wind and stuff to remove the heat created. And T5's produce the same amount of heat as Mh watt by watt so ive heard.

I use T5 in my freshwater and Mh in my saltwater, i like MH more simple because it is more compact and can have a nice sleek look if housed somewhere nice which is a big plus for people without canopies.



EDIT: May as well add a few more things:

As you may already know all the MH light is produced from one small area, my 150 watt light producing area is about an inch long and half an inch wide, this gives you pros and cons, the good thing with this is that directly under the bulb will have a lot of light, more than T5, the problem with this is that all the light is concentrated into the center and the PAR/Lumens decrease in the sides of your tank that isnt near the MH bulb. So lets say directly under the light there is 1000 PAR, and at the edges of the tank it has 200 PAR, the average PAR will be 600 PAR but it isnt 600 PAR throughout the tank. Having this concentrated light helps you in these ways: Asthetic, being concentrated it will produce shimmer lines as well as shadows, Good for positioning all sorts of corals, you can put light demanding near the bulb and not so light demanding away from the bulb. But the cons can be cant really have light demanding corals at every corner of the tank, this is the reason why many sps owners choose T5's:

T5's light is produced throughout the length of the bulb, this gives an even PAR/Lumens rating throughout the tank, so lets say there is 600 PAR everwhere in the tank, this gives you an average of 600 PAR, notice how it is the same as the MH's? But with this you wont be able to get the 1000 PAR like the MH gives in certain areas. Since T5;s produce light in a non concentrated area, it wont give shimmer lines. But you will get even light throughout the tank so you may be able to put light demanding corals anywhere if you have the right light to start with.

There are lots of things to consider, also note that you can mix both T5 with MH to get best of both worlds. Do your research and you shall make the smart decision.