Hours of MH Lighting and Height above Water

[Elmo18]

I would like to know how many hours of metal halide lighting you are providing your tanks.

In addition, please also measure the height above the water line

- Elmo

P.S. If you light your tank with MH longer than 9 hours, please vote for either option 5 or option 6.

 

[coralseas]

yea
the need is to keep the light bright , so depending on your coral depth, and splash from fish
i keep my 400w about a foot cuz there so bright , but i used 250 and had them about 3inches ,
and the light stays on for about 11.5 h
around the equarter days are 12 to 14 hours apon seasons

 

[CarlaW]

My 400w radiums are 13" above the water line. If I drop them one link on the chain, I have heat issues!!
The maximum time is 9 hours.

 

[Scooterman]

12 hours, about 8" off the water
I have 4" fans blowing directly on the MH bulb at the end of the reflector.

 

[lizardarm]

12-13 hours a day, 11" above the water surface.

 

[BCT182]

I don't want to change the topic of the thread, but doesn't it stress out the corals and increase the chance of an algae bloom if you have your lights on 11-12hrs a day?

Oh, and I have Actinics on 10hrs and halides on 8 hrs. The lights are above the water line about 9 inches.
Brett

 

[Scooterman]

around the equater days are 12 to 14 hours apon seasons

We already are far from supplying the natural light as it is, depending on your corals most of them are in need of that much light. Stressing comes from sudden changes in light, yes that may affect them.

 

[BCT182]

Ok, I understand that. So sudden changes might be, increase in intensity or change in kalvin?

 

[Scooterman]

Lets say you go from a 250w lamp to a 400w lamp same distance, this would probably be a no no. Length of time on can also affect a coral if you say go from 6 hours a day to 12 all at once. So in general you don't want to do anything that would cause a shock to the coral, it would almost be like you jumping into a swimming pool freezing cold.
So acclimation is when you introduce the corals to these changes slowly, you can do this by placing the light farther away at first & slowly each day later move it closer & closer. Same with the amount of time you keep the lights on. Kelvin is the temp. lamp being used (color we see) which I'd imagine could have some effects, but I don't think it would be a major issue here.

 

[dnjan]

If you have a decent reflector, distance above the water (for reasonable distances, say less than five feet ) has almost no effect. Most people remember something from a physics class about light intensity decreasing at a rate proportional to the cube of the distance from the light, but they forget the conditions for which this applies. The assumptions are:

point light source

no reflection

no absorption of light due to the medium it passes through

While a MH bulb can loosely be assumed to fit the point-source definition, the other two assumptions are way off for most aquarium setups. First, we use reflectors. A correctly-designed reflector puts more light into the water than than the bulb itself. This is because the light from the reflector hits the water close to perpendicular to the surface. At close to perpendicular, more of the light penetrates the water surface, and less is reflected away by the surface. Light coming from the bulb, however, hits the water at an angle (except for directly under the bulb) More of this "direct" light is reflected off the water surface.

Once light gets into the tank, some of this light is absorbed by the water. Light absorption in air, however, is almost nothing compared to absorption by water.

So, first, use the best reflector you can get. And then, put your light whatever height works best for you in terms of heat and water splashing. And don't worry that by putting your light a few inches higher, you are measurably reducing the amount of light getting into your tank.