Two or three years ago, I had the idea of producing ‘a better moth trap’ using LEDs. Since then, several hundred people have read that blog post and several readers have made their own traps. One reader has produced a commercial version of an LED moth light and written a scientific paper on its efficacy.
About a year ago, I started work on producing another LED lamp unit designed to either operate either singly or as an array. The idea behind the concept was that a unit of 4 x 3W LEDs; royal blue, emerald green, UV and ice white, could be combined on a single heat-sink that was structured in such a way that one unit (12W) could be used as a bar in front of white sheet, two (24W) could be used in a V-shaped formation on a Skinner-type trap, and that four (48W) could be combined into a square array that could replace a mercury vapour bulb on a Robinson-type trap. Last night, I tried out the Skinner array (24W max). I chose the night based upon the fact that it was the time of year that the Giant Peacock Moth makes its appearance. These spectacular moths are up to 20cm across and are Europe’s largest moth.
I powered the LEDs from an old laptop ‘brick’ power supply that is well-capable of providing the high currents necessary. I chose to run the LEDs in series rather than in parallel. This has the disadvantage that the different colour LEDs drop different voltages and thus do not all run at the same power. However, it works well enough and the power supply was for free. As this was the first outing for this particular trap, and I was unsure how the heat-sink would cope, I put two hefty diodes in series with the 15V supply to drop the voltage by about 1V. Running the lamp on the bench I had found that this resulted in running at about half power. However, the lamp is still astonishingly bright and the heat-sink does not even get warm. The diodes used to drop the voltage do warm up a bit, but being 10A diodes they are well able to cope with this, and they get warm rather than hot to the touch. Next time I run the trap, I will do so with only one diode in the supply line (about 14.5V).
It was a warm and cloudy evening. I had not expected much. However, the results were nothing short of astonishing. I had hoped to attract a Giant Peacock Moth. However, instead they came in numbers. At first they flew around and it was hard to tell how many there were. One, then two, then three, then four, then five entered the trap. Two males that had been fluttering in the eaves of the covered terrace, settled quietly on the beams. One settled on the outside of the trap. I began trying to photograph them. While I cannot be sure, there were at least 8 or 9 of these moths and with several in flight around me, possibly as many as 15 or 20. These were not of course the only visitors. There were several hawk moths including a beautiful Elephant Hawk and dozens of smaller moths together with many beetles. Since the object of the evening was the Giant Peacock Moth, I paid little attention to the many other species.
The bottom line to this report is that the V-shaped array works very well with a Skinner trap. I believe the overall philosophy is correct – an LED light source that is rich at the blue end of the spectrum, tuned to the peak absorption of moth (and beetle) photoreceptors. I would add that my entire trap cost about £25 (not including the cost of the power supply). ‘Brick’ power supplies from old laptops are practically free at boot fairs or can even be had from new on eBay at very low prices where the laptops they were designed to be supplied with are now considered defunct.
I am writing a little blog-post on the Peacock Moth – you will soon be able to find it at petermobbs.com.