Objective lighting measurements
 

Just curious if there is a way to objectively say what "high" lighting level is versus "low" or "moderate". is there a standard Watts/gal measure to go by? or a watts per inch depth? i would really like to keep some coral that requires moderate to high lighting, but can't afford a MH fixture..

There for sure is an objective way to measure the amount of energy a light gives off. Its called the "par" of a light and it varies depending on depth of water in your tank.

But, this is pretty useless becuase I can't really think of companys that rate there lights like that.

I think what you might be looking for is t-5's. These are florecent lights that give off enought juice to keep any type of corals. Now, what kind of t-5's you need I have no idea because I have metal halides.

Here's Sanjay Joshi's lighting guide which is the best objective resource for MH lighting.

http://www.manhattanreefs.com/lighting

I'm not aware of any for fluorescent lighting although Grim Reefer on Reef Central has done a lot of PAR measurements for T5HO bulbs on his thread there.

I've got a 96 watt fluorescent coralife fixture for my 30 gal hexagonal. Would that be enough light for a highly photosynthetic coral? how high up in the water column should i keep it? I've got a wall (see photos) so i could in theory keep it at any height i wanted, but will that fixture be enough?

Are T5s that much cheaper than halides in the long run? I've seen quite a few threads on the matter and it seems like t5s need to be changed out more frequently than halides? So even though the bulbs are cheaper it balances out ? Anyway, worth looking into that aspect. Again there are quite a few threads in the whole halide vs T5s debate, just do a search.

96 wats of power compacts is not very much at all as your main source of light. You may be able to keep some softies and polpys but no sps, clams, or anemones. You may have some luch with LPS if you keep the, high enough in the tank.

T5 bulbs last just as long as MH bulbs if they are run the same ammount of time.

I don't know about that.... My roommate runs T5's on his tank and he has to replace bulbs about 4-6months where as MH seem to last upward of 10-12months...

^^^^
t5's can be run for up to a year but like MH you loss alot of output. Your die hard t5 guys will run bulbs 4-6 months max just to keep maximum output from the bulbs. For MH+T5's really aren't there for growth but for pop so you can still keep your bulbs up to a year.

I personally think t5's are more expensive in the long run, esspecially when your replacing 6 bulbs twice a year which costs $200 or more, let alone running a 10 bulb system.

With the amount your save on energy, your just spending more on bulbs. So imo, MH's are cheaper to run.

as for the original question, light is not the only issue to have to look into when it comes to corals. Flow is a big factor as well. In some cases just to keep one type of coral you will have to place another under a ledge or in a lower flow area.