# Lighting Deep Tanks



## Raul-7 (Feb 4, 2004)

I heard if you have deep tanks(24") it's better to use MH than PC, is this really true? If PC were used would this cause Glosso and the such to go bad? Would having a deep(4") substrate solve the problem? :?


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## plantbrain (Jan 23, 2004)

A 24" deep tank at Albany had no issues using 2.1 w/gal of lighting, some PC some NO FL's growing all sorts of plants including Gloss, Rotala macrandra, Eustralis etc.


Regards, 
Tom Barr


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## gpodio (Feb 4, 2004)

I don't know how much I believe that a couple inches makes such a big difference. Unless your water is tea colored, a couple inches are not going to make much of a difference IMO. Specially considering that the light inside the tank mostly reflects off the glass walls rather than penetrates it and is lost. I think the major issue with taller tanks is other plants creating shadows. If I'm right, then a point-form light such as MH would actually increase the amount of shadows compared to a light source that is more evenly spread out accross the surface area of the tank. Just like sports fileds have multiple lights to avoid shadows, something similar can be said about our tanks. When I moved my 96W fixture (3x32W) from the 55 gallon to the 90 gallon, it really didn't make a lot of difference to the lower plants, they seem to grow just as well in the 90 as they did on the 55. Even when I changed from a 10 to a 15 high I can't say I noticed much difference in plant growth, but the plants are now able to grow taller in both tanks and therefore shadowing is a bigger concern for the lower plants.

I may be wrong, I can only speak for the 4" difference I have experienced myself and it didn't seem like much changed at all. I'm about to finish a MH fixture but I doubt I can compare it to what I have now, 100W of MH emits more light than 100W CF so the comparison is probably not very fair.

Perhaps reflector efficiency could make a bigger difference. I'm sure a good parabolic reflector on a MH bulb can penetrate far deeper than any linear reflector, MH or CF.

Giancarlo Podio


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## Steve Pituch (Jan 25, 2004)

Maybe with regular old fashioned T12 fluorescents, but with the AH Supply reflectors I think CF lighting is pretty intense.

The 175 Watt MH pendant lights are focused more, so you will have one area slightly brighter. However I think the dropoff side-to-side is greater with MH. People used to say they liked pendant MH because it went better with open top tanks and the ripples in the water would create shimmering shadows on the substrate, and feel this is more natural. But because of this focused aspect there are shadows in the tank where ever there is a leaf. The light doesn't diffuse to the bottom under the leaves like fluorescent light. Therefore with MH pendants you have to be very careful about floating and emergent growth blocking light below. Even one stalk of say Bacopa carolina can block light to put the bottom of the plant in shadow.

With the 55W and 96 W CF bulbs coupled with AH Supply's super reflectors, I think that you can put together a combination that will punch through all that water and evenly illuminate the tank.

I have a 125 gallon tank that is about 22 inches high. I have a soil substrate which is 4 inches thk by necessity. It does help. But then did you buy the tank because of its depth? In this case just worry about getting your hands down to the bottom of the tank to plant those critters. :wink: 

Steve Pituch


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## plantbrain (Jan 23, 2004)

Does the added depth of the substrate a factor or is it the volume of the substrate that is better for the plants and has nothing to do with the lighting?

I think what has been said about shading does play a significant role when comparing PC/linear tube FL bulb's vs MH's. 
I've had both for many years.

My solution is to use the HQI double ended small 150w bulbs closer together, these take up less room, look great and provide good spread vs the ugly MH Globes.

A better MH reflector certainly helps but you still have self shading issues that are not as significant as with long PC tubes etc.

I would even say that the PC bulbs cut off at the ends and the middle of 2x55w on a 4 ft tank are significant vs a T-5 bulb but these are still too expensive in the USA along with HQI double ended lighting.

But the cost will come down later.
150$ for a 150w small HQI double ended pendent that looks much better than those Hamilton/Corallife globes(which go for about 250$ ea).

Electronic ballast will extend bulb life considerably and also increase output and reduce noise down to zero.

But these cost more, 
Regards, 
Tom Barr


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## MiamiAG (Jan 13, 2004)

I'm posting a response George Booth gave on the APD back in 1995. I think he has a firm grasp of the factors you need to grapple with in lighting a deep tank.

Don't think so much in terms of inches but in terms of lumen/lux/par at the leaf.



> The discussion on light requirements is tending toward opinions based on "What works for <insert your name here>". This is all well and
> good, but doesn't provide much basis for determining "what will work
> for me" based on "what works for you". There are quite a few variables:
> 
> ...


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