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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
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.