spread out light or concentrate?

[itZme]

Hi,
I am building a 72"x18" canopy for a 140 gal and wondered if it would be more beneficial to have 3- 250 watt MH or be just about the same as using 2- 400W MH? I plan on using reflectors on the MH and also have 4- 36" flourescents too.
I can get the 400's for about the same price as the 250W and when I thought about it I would only have a 50W difference but about $100 savings by only buying 2 sockets/ballasts/bulbs. The tank is 25" tall and the lights will be about 6 inches from the suface with 2 fans pushing air into the hood and 2 fans drawing the hot air out ---> like this --->

Also, is there any advantage/disadvantage with using 14K instead of 10K bulbs? I haven't decided what types of corals I will have yet but really like pictures I have seen here of the colorful ones like sun coral.

Thanks for any advice,
-- itZme

[FragOutpost]

Using the 2 400 watt lamps will provide more overall intensity but the center of the tank will receive less light as compared to the 3 250's. It is a tough choice between the 250's and the 400's. What is your overall goal witht the tank? What kind of corals do you plan to keep? Is this more of a display type reef or a propagation setup?

The 10K bulbs will tend to be yellow or crisp white while the 14K will be a bit bluer. Generally speaking the lower the Kelvin rating the higher the PAR level. (Photosynthetically Active Radiation)

Here are some links for comparison -
http://metricksystem.com/chris/250wcolour/
http://www.cnidarianreef.com/lamps.cfm
http://www.coralreefecosystems.com/ltg_bulb_color.htm
http://www.diyreef.com/lcomp.htm

Hopes this helps!

[D12monkey]

The rule of thumb ing placing light is each light is most effective in a 24 x 24 area underneath the tank. Your tank is 72 in across. SO my recommendation would go with 3 bulbs. Now the wattage is going to be up to you. I presonally went with a 250w Metal halide due to my tank being 24 in wide. The main reason I went with the 250W is the power consumption between the 2 bulbs versus the intensity of the light. I haven't come across a coral that I needed a 400W system yet. the 250W would preform excellent but the 400W would provide a faster growth rate. Also you have to take into consideration that the color specturm of the bulb will also affect the coloration of the corals. The "bluer" you get, meaning the higher up the kelvin scale you go, the slower the corals grow but the more colorful the will get. Real sunlight is at a 6500 Kelvin range. But that will look yellow to our eyes. A bluer hue will more appealing to our census. I've used a 14,000K bulb and 10,000K bulb and now am using a 20,000K bulb. With the 10 and 14000 K bulbs I felt I had to augmentate the bulb with actinic bulbs. With this 20,000K bulb I feel that I don't have too. But we shall see as it's only been on for 1 day so far. Also with the depth issue of you tank either bulb would work with it. If you had a 26 In tall tank I would've said go with the 400s if you wanted corals to the bottom of the tank. But the depth of your tank will allow you to use either system and get good results.

[Peterock]

I would diffently go with the 3 250watt, and I would offset the system with having 2 14k bulbs on the ends and 1 20k in the center or vise versa to help stimulate both good growth and color. I am setting up a huge 250 gallon frag system thats only 17 inches high and I am using 4 175 2 6500 watt and 2 20k that i am using for my business to grow my SPS and high light corals. So you should be fine with the 3 250's

[FragOutpost]

Originally Posted by Peterock

I am setting up a huge 250 gallon frag system thats only 17 inches high and I am using 4 175 2 6500 watt and 2 20k that i am using for my business to grow my SPS and high light corals.

Are you building the tank yourself, and if so are you using glass or acrylic? What are the dimensions of your prop set up, 72"x48"x17? Can't wait to see some photos.

[Peterock]

You got it 72x48x17 just so that i can make sure the corals get high growth but also get wierd growth paterns. My business partner and I will be building it here in about 1 month or so after the $ gets flowing.

Here is a pic of my canopy that i built for my 72 bow it is 17 inches high with my MH being 11.2 inches off the water.