I am at the design stage of new lighting for the new tank and a number of considerations are becoming apparent. Tropical reef tanks largely utilise light at the blue end of the spectrum, many reefkeepers seem to use lights in the 10000 - 20000K range. Stony corals seem to thrive best under these conditions and undesirable algal growth is inhibited.
However, in a temperate reef, algae is far and away the dominant natural feature. Therefore it seems likely that warmer lights are required. Natural sunlight is in the region of 5600K. This casts a yellowish light within the aquarium that isnt as attractive as the cooler higher ranges.
If we take 'white' light at 5600K and pass it through clear water the red end of the spectrum is effectively filtered out within 15metres. It might follow, therefore that unless we are collecting plants at depths greater than 15m we need to provide full spectrum white light.
I have built a temporary light hood, its a plywood board 1600mm long by 400mm wide. I have fixed 8 no. 3 light spotlight fittings from B&Q and fitted 15 no. 'cool white' LEDs and 9 no. 'warm white' halogen lamps (supplied with the spotlights). I understand that the cool white lamps are in the region of 7500K and the warm white lamps about 4500K.
The overall effect appears very natural with a pleasing 'ripple' effect. Although designed as a temporary measure to get some light into the tank whilst waiting for new lights to be manufactured I am beginning to wonder of these may be adequate for the job. To be honest its primarily down to cost:
new LED light panel - 450 W £1000.00
my own light panel of 24 lamps, 15no. @ 7W and 9no. @ 50W has cost £480 so far. I paid £20 each for the LEDs, double the usual cost because they are dimmable. However, I can return them for double the amount of non-dimmable ones. The cost of a LED GU10 bulb is £9.00. I would need 64 to acheive the same amount of power consumption as the manufactured LED panel. At 50W equivalent output that is 3200 Watts of light into the tank!
There are pro's and cons for both. The manufactured panel has an output of light that I cannot replicate using spotlights, I simply could not fit 22 of the B&Q fittings over the tank. It has built in cooling and uses LEDs of a known fixed colour temperature. A mix of cool white, blue and red lamps of a ratio of 25:10:10 respectively, of 45 10W LEDs should be both aesthetically pleasing as well as giving light at the corect spectrum for macroalgal growth. However, if any LEDs fail I will be unable to replace them easily - each is individually soldered.
My home-made hood allows easy changing of lamps. It is likely that better, higher output lamps will be available over time. GU10 fittings are readily available and available in blue, cool white and warm white.
I could fit another 18 lamps on my hood. An extra 6 spotlights at £9.00 each (each has 3 lamps) would allow a total of 42 LED GU10 lamps at equivalent 50W output giving 2100 W whilst consuming less than 300W. A mix of cool and warm white with maybe 3 or 4 blue should come somewhere close to giving the right result. The cost would be 24 spotlights at £9.00 each and 42 lamps at £9.00 each a total of £594.00, about 60% of the cost of the manufactured panel with 2/3rd of the output, no built in cooling and a bit 'Micky Mouse'!
Obviously the manufactured panel is going to be better. Its just the outlay.
I've added some rocks with macroalgae growth and placed them under the lamps. I'll give it 2 weeks and see how they fare before making a decision.