How cool is your light?
Keeping your aquarium lighting (T5) at the correct temperature is more important than you may think. The optimum temperature is 35°, keeping your lighting at this optimum temperature will improve output and efficiency as well as improving the life of the bulbs. The spectrum of all T5 bulbs shifts over time, too much heat or running your bulbs too cool will speed up this shift in spectrum.

It is a common misconception that the cooler you run your T5s the better; it is actually more detrimental to the efficiency of the bulb as them being run above the recommended 35°. There are lots of products on the market that advertise the fact that they have lots of built in fans, however as well as the increase in noise and power consumption over cooling will have a negative effect, any temperature above or below 35° will reduce lumen output.  (Graph 1)

As you can see from the graph above the optimum operating temperature for a High Output T5 is 35°C and the effect of under or over cooling has on the light output of the bulb (Figure 1) and the comparison of running temperatures between a T5 tube and a T8 tube. A T8 tube has a slightly lower optimum running temperature than a T5 at 25°C with less of an impact with slight temperature change.
There are two methods of cooling: active cooling and passive cooling. Active cooling is something we have already touched on; using fans to cool the bulbs and passive cooling is the use of a heat sink to dissipate the heat away from the tubes
Another area of lighting that is often over looked is the ballast of the light unit. A ballast runs most efficiently again at 35°C. Some units have the ballast and the bulbs next to each other so the heat is directly passed from one to the other instead of being dissipated away from the tubes and ballasts directly.
The iQuatics’ series 2 AquaLumi have the bulbs and the ballast in separate compartments; this allows the passive and active cooling to dissipate the heat away from the tubes thus preventing heat transfer from one heat source to the other. Some units will only cool the bulbs and not the ballasts, however if the bulbs are next to a hot ballast this method of cooling becomes completely ineffective.
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