SDG #183 Cree XHP70.2 Aquarium Light with PCBs from PCBWay

This is the first stage of a custom aquarium luminaire built around the Cree XHP70.2, a large-die, high-flux emitter that can be driven at either 6V or 12V depending on the die configuration. Rather than buying an off-the-shelf reef light, the build starts from bare custom PCBs, which keeps the thermal path short and lets the emitter spacing be matched to the tank footprint instead of to a manufacturer’s marketing photo.

The interesting engineering content is in the trade-offs. Emitter choice is discussed in terms of forward voltage, current handling and flux per watt rather than headline lumen numbers, and the optics section explains why a bare XHP70.2 over water is a poor idea: without reflectors or lenses, a large amount of light lands outside the tank and never reaches the corals or plants. Measured optical efficiency figures back that up and show how much output a suitable lens or reflector actually recovers.

Assembly is done with solder paste and hot air on the custom boards, which is a useful demonstration for anyone reflowing large thermal-pad emitters at home; the pad geometry and paste volume matter far more here than on ordinary SMD parts. Thermal testing then checks junction temperature behaviour once the LEDs are mounted, since running a 70-series emitter hard without adequate heatsinking is the fastest way to destroy both output and lifespan.

For anyone planning a DIY aquarium or high-power lighting project, the takeaway is that emitter selection is the easy part, while optics and heat management decide whether the finished light is actually better than a commercial fixture.