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Lighting games (g)

I asked some time ago if anyone had tried the Dupla Milux lamps which 
utilise an 18 W Osram compact fluoro, but got no replies.

I've been running two 30 W Coralife Trichromatics mounted about 6" above 
a 3 foot tank - say 7" above water level - and wanting to get more light 
which was going to mean new fixtures since there was no more room anyway. 
I saw the Milux and they're very effective with 2 atop a 30" tank but I 
couldn't get any specifications or anything.

In the end I borrowed a light meter and took some readings. At tank top 
level I was getting around 8,200 lux in the centre of my tank and around 
3,900 lux at the ends with the two 30 W tubes and the single fittings 
lined with mylar. At the same distance directly under one of the Milux I 
measured around 11,300 lux but it fell dramatically to the side - not 
really all that  noticeable in the water. They were mounted around 16" 
apart and I figured I'd need them around 18" apart on my tank which is 
slightly longer. I tried moving them a couple of inches further apart and 
the lighting levels in the tank dropped slightly - I couldn't determine 
how much. I figured I'd really need 3 on my tank and the price was just 
too high at a bit over $200 Australian a lamp. I could stretch to 2 but 
not 3.

That left me wondering about metal halide - I could get a 150 or 175 W 
fitting for $400 or looking at normal fluoro tubes. Based on Dupla's 
recommendations at the back of TOA, the metal halide was overkill so I 
decided to run with ordinary fluoros and to move to 4 ft tubes which 
reading the info at the Krib and various postings here indicated were 
more efficient. In addition there's an interesting diagram in one of the 
appendices to Delbeek and Sprung's Reef Aquarium Vol 1 which shows the 
light distribution pattern from an array of fluoros. The brightest area 
is in an ellipse at the centre of the tubes and at right angles to them. 
Levels fall considerably towards the end of the tubes so the overhang 
wasn't likely to mean much in terms of loss of light - it would actually 
help me to get higher levels at the end of the tank than I could expect 
if the tubes were the same length as the tank.

I bought a twin tube 4 ft reflector and moved the mylar from my 2 single 
tube fittings into that. With 2 Auvlux (never heard of the brand) 36 W 
5,000K triphosphors (3,150 lumen rating), I'm getting 11,400 lux at tank 
top in the centre of the tank and around 9,400 lux at the ends of the 
tank. That's better than a 33% improvement in the centre and more than 
double the levels at the ends of the tank for an extra 12 W power 
consumption. I don't know what the CRI for these tubes is but, based on 
appearance and previous lamps, I'd guess it's above 85 - the appearance 
of the tank is very natural and no obvious colour abnormalities.

I'm impressed by the increased efficiency of the 4 ft tubes and the cost 
of the 5,000K tubes was $12.50 Aust each. I've been paying around $45 
Aust each for the Coralife tubes so costs are much cheaper. Assuming 
comparable tube life, 2 complete retubings and I will have recovered the 
cost of the fitting. I can't argue with the economies.

I'm still impressed by the Milux lamps and I think I would have got a bit 
more light than I've achieved had I used 3 Milux but I definitely 
couldn't justify that sort of cost (I could get a bit more light into the 
tank simply by lowering the lights slightly bbut I like having the space 
in which to work). If anyone can come up with a cheap, high quality 
pendant type reflector that takes the Osram 18 W compact fluoros, I think 
the results would prove considerably better than a simple reading of the 
lamp's lumen rating would suggest. Punching all of the output down in a 
much more focused beam than you get from the lamp in a normal fixture is 
very effective. I also like the point source lighting effect you get from 
water movement with them - similar to metal halides.

Since I just mounted the 4 ft tubes today I can't comment on their effect 
on plant growth yet but I've got hopes - boy, do I have hopes (g)!

Since lighting is such a perennial issue, I hope these observations are 
of some interest.

David Aiken