question for you metal halide gurus

[bigfruits]

i know that the common rule is 1 metal halide per 24" of length of tank. if i have two metal halides on a 36" tank will i get more light in the center of the tank at a certain depth?

the reason im asking is because id like to keep crocea and maxima clams in an 18 inch deep aquarium. id like to use 150 watt metal halides but i think if i have the clam on the sand it might not get enough light to thrive from only one bulb. but if i have 2 150 watters im guessing that although each individual bulb will not penetrate deeper, it will still get more light because of the short distance between each bulb (2 bulbs on a 36" length). obviously the left and right side of the tank would only benefit from one bulb but the middle area between the two bulbs where the lights "overlap" would have a higher PAR. am i correct?

hope that makes sense.

thanks in advance
-z

 

[bigfruits]

bump

 

[hahnmeister]

dont worry... you would be surprised how low of light croceas can actually tolerate. with what you are talking about, you shouldnt have any problems. croceas can tolerate much higher light levels, but by no means is it a requirement.

As for the lighting effect you are talking about, yes, you are on the right track. The light fields will overlap and the outputs will be higher in the center of the tank than at the edges. The intensity may be better at the bottom than with a single 250watt bulb even, as the more spread out a light source is, the less it will diminish with distance... as dictated by the inverse square law of a point source. This is how T5s compete with halides so well... they distribute the output of a 250watt halide output over a 12"x36" area... so even though it is less intense at the top (because the light isnt as concentrated at the top) the light penetrates farther. The tradeoff, and one you should know of as well, is that the light levels will be less intense at the top of the tank compared to one larger bulb. But, you will have a wider/greater spread of that light at the top.

 

[Blown 346]

You will have plenty of light as advised as above.

 

[Napervegas]

I had a 36 by 18 tank, I for a long time i ran it with 4 36'' vhos, then i tried 2 vhos and 1 400w mh, it looked good.

 

[drives300]

metal halide

metal halide

Also I believe clams like 10 k lighting from what I hear. I think with dual 150s you may be ok with 14k

 

[hahnmeister]

The idea has been that clams like 10,000K lighting because 10,000K bulbs often have much higher outputs than 14,000-20,000K bulbs. Its pretty much a myth though. The PFO solaris, as well as numerous people running 20,000K bulbs over them (myself included) has shown that they like any spectrum of bulb, and not even as bright as you might think. Sure, they can tolerate light levels much higher than most any coral can, but they dont need it. Very tolerant animals.

 

[michaeldaly]

18 inch is actually quite shallow.