MH bulb orientation question

[Bob I]

It is always recommended that you orient a bulb perpendicular to the front of the tank. I never knew why. Perhaps there is better light dispersion :question: . One of my lights is oriented that way. Yesterday I hung a pendant above my other tank, but due to space constraints I hung this one parallel. I have noticed that the ripple effect is much stronger with the parallel orientation. I am wondering if anyone knows why :question:

[danny zubot]

I think the rippling effect in the water is based on the reflection in relation to the current at the water surface. In other words its the type of flow you have in your tank.

[Delphinus]

On the parallel vs. perpendicular, that depends on the reflector design. As to why it would make a difference on the rippling, I have no idea. One tank I run parallel and one tank I run perpendicular and I have never noticed a significant difference on the rippling, however the tanks in question have different flow patterns so it wouldn't be an apples to apples comparison.

[Bob I]

I think the rippling effect in the water is based on the reflection in relation to the current at the water surface. In other words its the type of flow you have in your tank.

Yes of course, you have an excellent grasp of the obvious. :biggrin: Probably my fault for not mentioning that both tanks have the same amount of surface agitation. :mrgreen:

[Canadian Man]

Because you use Aqua Clear hang on filters on your tank and they create current back to front rather than the typical side to side that most people have?

did I get the answer correct? :biggrin:

[Bob I]

Because you use Aqua Clear hang on filters on your tank and they create current back to front rather than the typical side to side that most people have?

did I get the answer correct? :biggrin:

If it were only that simple. :eek: I don't use Aquaclear filters. My surface agitation is caused by Fluval returns both pointed the same way. The ripple effect is still stronger with the bulb oriented parallel. The pendants are the same. Therefore the only physical difference is the way the pendants are nounted. I am curious why perpendicular mounting is recommended. :question:

[Canadian Man]

Last I heard most people don't have a wide enough tank to run the bulbs perpendicular. The reflectors most people use apparently have a wide spread so if one was to run a reflector designed to run perpendicular, parallel than you would be wasting some of your light spread to shine outside the tank.

I think :biggrin:

[Bob I]

I appreciate your thoughts, however, it does not answer the question as to why bulb sellers make the recommenndation to go with perpendicular mounting. :sad:

I may have to go to the source, and ask them why. :idea:

[Delphinus]

Well, you could do that of course.

But really, like I said earlier, I think what you're referring to has more to do with the reflector. There are reflectors for parallel mounting, and reflectors for perpendicular mounting. The perpendicular ones either reflect more light into a given area, or have a focal shape that lends itself for better coverage for that of a "typical" tank.

Let me ask you this ... do you think it would matter on a cube tank?

One thought that I have, given that in your situation nothing else has changed (i.e., the surface agitation doesn't care which way the light faces), but, a halide bulb doesn't exactly emit a perfectly diffuse light coming out of it. For example, how come many pendents don't mount the bulbs vertical?

Anyhow, I assume it's a slight polarization effect. Just like with polarized lenses on sunglasses, it matters which way they're oriented. If the light waves travel parallel to a in a certain plane, and corresponding to the resulting waves/agitation orientation of the water surface, the angle of intersection will be different between a parallel mount and a perpendicular mount.

Anyhow, there are my thoughts.

[Bob I]

Tony hit on something I had not considered. As both my tanks are close to cube shaped it should not matter. I did notice with a little experimentation that the ripple effect changes dramatically with the height of the bulb above the tank. I have found that with the height about the same the ripple effect is the same.

Unfortunately that still leaves the original question; Why is the perpendicular orientation recommended. :question:

[StirCrazy]

Tony hit on something I had not considered. As both my tanks are close to cube shaped it should not matter. I did notice with a little experimentation that the ripple effect changes dramatically with the height of the bulb above the tank. I have found that with the height about the same the ripple effect is the same.

Unfortunately that still leaves the original question; Why is the perpendicular orientation recommended. :question:

the shape of the bulb. you can shift it closer to the back and get full coverage to the sides. as because of the base at one end the bulb will project farther to the opposite end and then on the sides it will have the greatest projection. so since most people are running tanks that are 18" front to back (at the time when this was set as a rule) and 4 foot long you get the best coverage bay moving the base of the lights to the back of the tank.

here is a pic to better describe what I mean

http://members.shaw.ca/crystalk/lightingconfig.JPG

Steve