Light Requirements

[twps]

I apologize if this has been covered in another thread, I did a quick search and skimmed through some older posts, but didn't see anything.

As I typically find in this hobby everyone has their own opinion/suggestions.

I have a 46G bow with Aquatic Life T5HO 39W bulbs (1 white/1blue) I understand this is 10,000K lamp. When I bought it I was told this would be sufficient lighting for all corals, etc. I'm wondering if it truly is? I bought some frags from a guy who has a 55G tank, a little deeper than mine with the exact same lights. He's keeping a lot of nice SPS corals, and has been for 2 years with this setup. His tank seemed darker than mine.

Where I get more confused is how different people measure the light requirements differently, 10,000K for my tank is sufficient for all corals on some websites, others rate by watts/gallon which I'm then no where near having enough. I read one place I should have 3000+ watts on my tank to accommodate any corals, that's 70+ bulbs!

How do you measure to ensure you have the right amount of light for your tanks?

 

[Hiker4twenty]

From what I'm gathering you have a 2 bulb fixture with 39w T5's? If that's correct then you have 78w on your 46g tank which gives you 1.7 wpg. That is definitely not enough light for corals. You'll need to double you light output to successfully keep corals and even more lighting if you wants clams or SPS corals.

 

[daugherty]

the 10k, 6500k does not mean you can keep any coral with that light all that is is the color of the light a 6500k bulb is more yellow than a 10,000k light a 14,000k light is bluer and a 20k light is very blue. what you need to look at is the wattage of the bulbs. you will want to shoot for at least 4-5watts per gal with t5's to be able to keep anything you want in your tank

 

[twps]

This is why I am confused, based on wattage. But each type of light fixture produces different light spectrum's, kelvin's, wattage, etc. We all know a CFL bulb at 13W is comparable to an incandescent at 100W. I've seen on line (I'll post it if/when I find it again) that a T5HO @ 10,000K is equivalent to a 250W MH.

I'm not trying to debate or start an argument. I'm just curious what is the best number to go by? (ie. watts/gallon, lumen's. kelvins, etc.?)

For example in my case using T5HO's I would need 6 bulbs, which due to my take configuration I would never be able to fit on the top of the tank. I'm going to have a hard time fitting 4 bulbs honestly.

 

[twps]

This is a long, but interesting read which really suggests the old watts per gallon rule is archaic with new lighting technologies.

Aquarium Lighting; Kelvin, Nanometers, PAR, Bulb, Watt, MH, LED, light basics.

The concept makes sense when you think about it. A new CFL 7W = Incandescent 100W In this case what number do you use for the watts per gallon calculation?

 

[daugherty]

it is kinda archaic but not all bulbs are created equal. if you really want to find out about a bulb you will need to have a par meter to test the bulbs so that you are getting the most par you can. t5's are good lights that offer a hight amount of light as compaired to regular bulbs. but the downside to them is that they do not penatrate the water far enough to be good in deeper tanks that is where mh lights are better. the watt per gallon is still use to give people a baseline as to what they need by no means it is perfect. but i can tell you 2 t5's on your tank is not enough maybe for some soft corals it will be ok.

 

[Bifferwine]

For T5s, with everything taken into account, 4 watts per gallon is a good goal to shoot for. Having at least that will allow you to keep anything you want. It is hard to apply the watts per gallon rule to different types of lights, but it does tend to work well for T5s. What's more important than wattage for T5s is if each bulb has an individual reflector surrounding it. IRs are supposed to increase the light that gets to the tank by up to 300%.

I have never ever ever heard of anyone saying you need 3000+ watts for a tank your size. Even 10 to 15 watts per gallon is at the highest of the range of what you'd want.