is watz per gallon important?

[dre82584]

well i have 2 95 watts pc on my 30 gallon coralife fixture n then i have 8 55 watt bulbs t5's on my 72 gallon. leading it to .i have a 120 gallon tenacore tank and its only 53 inches would the t5 light fixture be able to hold down my corals? and it is about 3 inches more shallow then the 72 gallon.

 

[Deanos]

is it tru that u should have atleast 6 watz of lighting per gallon for your reef tank.

What kind of light are you referring to? Metal halide, T5, VHO, PC or normal output?

 

[alfani]

i have my T5 setup under 4.5w per gallon for a couple years now without any problem but my tank is mostly lps and softies. it's on for 7-9 hours

 

[fritz]

You really can't use watts per gallon as an accurate measurement. Different types of light penetrate water differently. For example VHO and CF bulbs can only penetrate about 6-8" of water. After that there isn't much intensity left in them at all. So then you can see why a 20 gallon high would need more watts than a 20 long. Or a 40 high would need more than a 40 breeder. No matter how much light you throw on top of a tank VHO and CF still can't penetrate, for example on a 2 foot deep tank even 800 watts of VHO won't get to the bottom 6 inches with any meaningful strength.

So if everyone had a tank with the same dimensions and everyone used the same type of light then you could use watts per gallon as an accurate measure. For reefkeeping most people go by depth guidelines. IE: 2 feet of depth and under requires 250 watts MHs. 2 feet and over require 400 Watt MH and smaller tanks can often use 150watt HQI MH bulbs. MH have a 2 foot by 2 foot spread (surface area wise) T5 usually requires 1 bulb for every 2.5 inches of surface width. Less if you have less light demanding animals. CF and VHO are good IMO only for supplementing the color of yellow MH bulbs and are not good by themselves as reef lighting. Some people do use VHO only on their tanks with success but for that much wattage I'd rather use MH or T5 as T5 has a very deep "punch".

 

[meschaefer]

Different types of light penetrate water differently. For example VHO and CF bulbs can only penetrate about 6-8" of water. After that there isn't much intensity left in them at all.

I have heard this said multiple times from what I consider to be reputable sources, yet i just don't understand the physics of it.

 

[lfsmarineguy]

I'm assuming it has to do with the water refracting weaker light frequencies more easily. The more intense the light the farther down it can get before it is useless. The same effect can be seen on a greater scale with the sun in the ocean. Go down far enough and you can notice the difference in the wavelength of the light that penetrates. Blues become the dominant spectrum not too far from the surface just before it goes completely black.

 

[meschaefer]

Absolutley, but the frequency of the light has more to do with the bulb temp, than the source of light that is emitting it. Reds and yellows are absorbed much more readily than blue light is, and as such blue light will travel much further in water. The statements that i have trouble with is that "No matter how much light you throw on top of a tank VHO and CF still can't penetrate" Why?

 

[ming]

I'm assuming it has to do with the water refracting weaker light frequencies more easily. The more intense the light the farther down it can get before it is useless. The same effect can be seen on a greater scale with the sun in the ocean. Go down far enough and you can notice the difference in the wavelength of the light that penetrates. Blues become the dominant spectrum not too far from the surface just before it goes completely black.

you're probably looking more for wavelength instead of frequencies. But yes, water is not completely transparent so it absorbs light as it gets passed though, and since the color of water is more blue, blue penetrates through it further then any other color

 

[ming]

Absolutley, but the frequency of the light has more to do with the bulb temp, than the source of light that is emitting it. Reds and yellows are absorbed much more readily than blue light is, and as such blue light will travel much further in water. The statements that i have trouble with is that "No matter how much light you throw on top of a tank VHO and CF still can't penetrate" Why?

its the intensity of the bulbs aren't strong enough to grow very light demanding corals. I'm sure its plenty for softies and LPS, but not most SPS.
Think of it as, 1000 pistol bullets will not pierce a tank's hull, but a single bazooka will go through it.
pistol bullets = VHO/CF bulbs
bazooka = MH/T5
Its not quantity, but quality of the lighting

 

[lfsmarineguy]

I think it has more to do with the light refracting properties of water since at less than 3' (most tank depths are less) there isn't enough color to really effect the light unless your water is yellowed by DOC. Most of the lights we use can't come close to replicating sunlight. For Fritz, I think the addition of other bulbs at the same output could be likened to shooting at a brick wall. If one bullet doesn't get through more of the same won't either. If you use a larger round you will get better penetration but none will go any farther than the other ones of the same. The lights aren't synergistic in that way, they don't add up to a bigger light.

 

[lfsmarineguy]

wow, that was weird......

 

[meschaefer]

its the intensity of the bulbs aren't strong enough to grow very light demanding corals. I'm sure its plenty for softies and LPS, but not most SPS.
Think of it as, 1000 pistol bullets will not pierce a tank's hull, but a single bazooka will go through it.
pistol bullets = VHO/CF bulbs
bazooka = MH/T5
Its not quantity, but quality of the lighting

Not a good analogy, a photon is a photon, no matter what its source. And I can't think of a good reason why photons emitted from one source, would be unable to penatrate water as well as photons emitted from another source. This is not to say that the PAR reading on different lamps are the same, but there is no reason that I can think of why "No matter how much light you throw on top of a tank VHO and CF still can't penetrate"

 

[lfsmarineguy]

Picture a flashlight next to the sun. If you flip the flashlight on and off from the same distance as the sun, you would never notice it (forget it will take awhile to get here). Yet if you stare at the sun it's like stabbing yourself in the skull sometimes, it hurts. Photons may be photons but the sun has more photons with more punch than the flashlight. Where did Sanjay go lol he could probably make us all look like noobs with this explanation.

 

[Wes]

true meschareefer, however the problem is VHO isn't very efficient at firing all of those photons down. MH penetrate deeper because all of those photons you mentioned are coming from a small point source rather than being spread out across a large surface area of a VHO tube. Not many of the photons from VHO are shooting straight down, thus less penetration.

T5s are able to penetrate deeper than VHO simply because their small diameter makes it easier to use parabolic reflectors that bounce most of those photons downward.

You can probably have VHO tubes completely covering your tank to the point where they are touching and you still have less photons shooting downward than a more efficient design like a good T5 or MH setup.

 

[ming]

Its about how concentrated the photons are. A VHO/CF bulb only produces so many photons and its spread evenly throughout the bulb. A MH would produce a staggering concentration in the center, and its less on the sides. The issue is that there isn't enough surface area for you to add more VHO bulbs to equal the same amount of photons as a MH.

Heres a better analogy,
Lets say you have a desk, which you wanted to put as many coins as possible on the desk, but not stack them, yet you only have pennies.
Penny = VHO
I wanted to do the same, but I have quarters.
If I had 20 quarters only, and you might be able to use a few hundred pennies, but I still have more money. If you stacked the pennies, I wouldn't be able to see the bottom one so they don't count.
Each cent = a photon so I have more intensity

 

[meschaefer]

I am not arguing about efficiency (i.e number of photons outputed by bulb- hell there are 250w MH bulbs that put out more photons than some 400watt bulbs), the statement I took issue with was this

"No matter how much light you throw on top of a tank VHO and CF still can't penetrate"

..this is the only statment I took issue with. this statement seems to state that the light coming out of a VHO or CH bulb, is somehow different than the light coming out of a MH bulb. It's not, there is no reason why VHO can not penetrate to the bottom of the tank.

 

[cali_reef]

..this is the only statment I took issue with. this statement seems to state that the light coming out of a VHO or CH bulb, is somehow different than the light coming out of a MH bulb. It's not, there is no reason why VHO can not penetrate to the bottom of the tank.

Matt, it is all about "point source", you can get all the photon of the VHO down to a 24" deep tank if you can come up with a way to focus all the photons, difficult but possible.

 

[ming]

"No matter how much light you throw on top of a tank VHO and CF still can't penetrate"

I would say it penetrates, just not in enough intensity for high light corals

 

[Chiefmcfuz]

All I know is my corals are much happier with my current 150 sunpod than they were with the PC fixture I started with.

 

[fritz]

I would say it penetrates, just not in enough intensity for high light corals

Yes it penetrates otherwise it would be dark. You said it spot on ming, if you test with a Lux or Par meter you'll see it drops off very quickly the deeper you go with CF or VHOs for the reasons mentioned. There are many an experiment on the internet showing this.

MH has the best punch due to the point source factor, T5 (with enveloping parabolic reflector), CF and then VHO.