Metal Halide - Choices

[sphelps]

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.

[Aquattro]

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.

[sphelps]

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

[daniella3d]

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.

Originally Posted by sphelps

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

[sphelps]

Originally Posted by daniella3d

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

[plutoniumJoe]

Originally Posted by sphelps

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.

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

[lastlight]

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.

[plutoniumJoe]

Originally Posted by lastlight

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

[globaldesigns]

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.

[sphelps]

Originally Posted by plutoniumJoe

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

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.