Metal Halide - Choices
 

After reading the following article http://www.advancedaquarist.com/2010/1/review1 I started to question what is the most efficient way to light a 6ft tank.

At present I have 3 X 250W MH which give me good coverage but I have seen many with 2 X 400W MH on the same length tank. It seems that you would get more over light but maybe not spread as evenly.

Any ideas?

What exactly are you asking? Efficiency for light vs. cost of running them? Or overall output for benefit of corals?
Personally I'm going to run 3x400w over my 6 foot tank, as I don't feel that a single bulb will cover 3ft adequately.

From the article though, those bulbs will be a consideration when replacing my radiums.

Based on pure numbers 3 250W halides seems more efficient than 2 400W halides. The type of ballasts might change this but really I wouldn't see the gain. Spread is based more on the reflector over the wattage so if you wanted to go with 2 400s you would want reflectors that light up a 3' square well like a lumenarc but then your tank isn't 3 feet wide so it doesn't really make sense. For halides you're probably better sticking with 3 250s, if you want to increase efficiency look into different reflectors as well as bulb and ballast combinations.

I agree that keeping the 250s would be better than switching to 2 x 400. The difference is probably not enough to warrant upgrading to 400 3 times.
FWIW, I was going to use 250s, but a screw up on my bulb order a couple of years ago put me into 400s (again). Now with a deeper tank, I'm sure they'll work better, especially running radiums.

Fun fact, 3 400W halides running 12hours a day will cost close to $40 per month in electricity!

What I am reading in the article though states that you get more light for less power out of two 400 vs 3 @ 250.

How is 2x400 less power than 3x250?

The 400s are going to burn 800 watts and the 250s 750 watts?

I'd stick with 250s myself. I know it's a dying breed but I've finally tracked down another hqi ballast for my tank. I can run my radiums as they were intended and down the road I can run a lower kelvin bulb and get super sweet par numbers.

That is what I always believed as well but you must take into account the power to drive the ballast as well as the amount of light they give off. So for instance a Vertex 400 watt ballast actually consumes 444watts with a ppfd of 121 so at 888watts you get 242 ppfd. Watts per ppfd 3.6

A vertex 250w consumes 263 and produces 52 ppfd for an output of 789watts at 156ppfd. Watts per ppfd 5

So for marginally more power consumption you are getting considerably more light. That is why I was questioning it. Maybe with 2 400 I can run the lights less consuming the same amount of electricity and get better results.

Does that make sense or do you loose out because your are not getting as equal of coverage with only two. I also think that I don't put much in the last 4-5" on the extreme sides of the tank so I can still clean the glass. Last consideration is that 2 400W bulbs are less expensive that 3 250s.

- Joe

I am thinking that 3 of the lower wattage, will add up to better coverage overall. While providing a more evenly spread of light.

2 of the higher wattage would be a smaller footprint, and give you hot spots.

Keeping in mind I didn't even glance at the article, what I think they mean is that you get more intensity out of the 400w bulbs than you do out of the 250w bulbs. You use 50 watts more using 2x400w than 3x250w, but the intensity you get out of the 400w bulbs makes up for that. So essentially if you get more intensity for close to the same amount of electricity, the efficiency is greater using the 400w bulbs.

Having said that, I still think you're better off keeping 3x250w over a 6' tank unless you get some sort of custom reflector for 2x400w that spreads the light over the 6' length, but doesn't spread it past the width of the tank. Now that would be interesting...

Sorry I wasn't thinking specific ballast data you used generic numbers so I thought I was missing something. My radium is a 250w and burns at around 333w so I fully get that. I always thought the e-ballast would use a little less. For example my same Radium on icecap uses 244W. Not sure if this was the old or newer icecap but I didn't think any e-ballasts overdrove bulbs.

Yes but that's just that one bulb, the same isn't true for all bulbs. Quite simply the 400W bulb in that brand produces a spectrum slightly more concentrated in the areas that add to ppfd. If you look at a different bulb like the Aquaconnect 14K it produces 83 ppfd @ 250 (e=33%) and 143 ppfd @ 418W (e=34%) on an electronic ballast (same as vertex). So basically the same efficiency which is more typical. And all this doesn't take reflectors and tank sizes into consideration. Even if you can get a little more efficiency from 400W bulbs how do you concentrate all that light over a 6 foot tank with only two bulbs? With 3 250W bulbs you can distribute the light better and make more use of it so realistically that is more efficient.
Like I said before it's more related to reflectors, bulb and ballast combinations over wattage.

Joe, it depends on what you want your tank to be. I get fine coverage and grow all sorts of high light stuff with 2x175W Vertex electronics running Iwasaki 15Ks under Lumenmax pendants. PPFD per watt, this is the most efficient set up according to Sanjay's figures using less electricity than 150W HQI system but putting out more PAR than some 250W systems:

http://www.canreef.com/vbulletin/showthread.php?t=59449

Understand that I have a mixed reef with lower light creatures too and my tank is on the shallow side for a 6-footer. Looks wise no one has ever noticed any dim spots. If you want a full out SPS garden, however, going with three 250W pendants is the better choice. You start getting diminshing rates of return once you hit 400W territory.

You can have a closer look when you come by for you macro later this week.

Those Iwasaki bulbs on electronic ballasts are a PAR breaker...not typical! You can't get the same PAR using different bulbs on that ballast. As long as someone is happy to commit to that one single bulb, that's a great choice! Pricey bulb though...

That sums up my radium conundrum. You sorta gotta commit to run them proper. Unlike that 175w choice tho you're not quite as ltd as you will get awesome par out of a ton of 250w bulbs tho you may burn them out prematurely (unlike with the radium).

Gee wizz..how much do you pay per kilowatt per hour? Here it's 7 cents. Surely not 40$ per month and why do you have to run it 12 hours?

That'S way too much I think.

Based on $0.08/kWh and that most 400W ballasts out there run closer to 500W a piece. So 1500W x 12hours = 18kWh x 30.4 (average days per month) = 547.2kWh x $0.08 = $43.78