A simple and inexpensive LED light trap for moth recording continued (from Part 1).
Since posting details of my initial experiments with LED moth traps I have been able to use the traps on many nights and also to compare the catches with those of a 12v 8w Actinic 'Heath' type trap which uses a fluorescent tube containing mercury vapour to give the ultra-violet light output. These are moderately effective, much less effective than the preferred Robinson 240v 125w moth trap, but reasonable portable and safe, not needing either mains electricity or a portable generator.
The biggest problem I had with getting the LED traps to work was the greater than expected current leading to over-heating of components and much greater drain on the battery than I anticipated. I struggled with working out where the power was being used, I tried changing the voltage regulator in case it was faulty, but the results were the same. On the data sheet for the LED tape the power consumption was given as 4.8 watts/metre, but my trials suggested it was at least 3 times that figure, way above what I thought it should be even with allowing for the power used by the voltage regulator. I now have seen that at least one seller (on Amazon) is giving the power consumption as 11.5w/m for the LED tape I am using and another as 14w/m for a similar tape. Suddenly my figures started to make sense, though I cannot see why the correct figures were not given (and still are wrong on the sellers Ebay page). But given the problems with the waterproofing (it is not uv stable) it should not surprise me. So I now call my 63 LED trap a 12w lamp not a 5w.
During the summer of 2017 I ran the trap on many nights, on some occasions catching more moths than I have ever caught with an actinic lamp. On 8 nights I ran it together with the 8w actinic trap so I could make a direct comparison, the results summarised are:
Total moths caught 301 of 68 species.
8w actinic trap 158 moths 50 species
12w LED trap 143 moths 52 species
Looking only at the Geometridae species the results were:
Total 119 moths of 28 species
8w actinic trap 49 moths 19 species
12w LED trap 70 moths 23 species
Similarily looking only at Noctuidae the results were:
Total 134 moths of 21 species
8w actinic trap 85 moths 18 species
12w LED trap 49 moths 17 species
It will need more nights running the traps together to get any meaningful (and statistically significant) data, the results are much more variable night to night than the summary suggests. It will be interesting to see if more data when I run the two traps together again changes these results. In particular if the apparent trends of more Geometridae species in the LED trap and more Noctuidae individuals in the actinic trap remains.
I also looked at any species that were only showing up in one or other of the traps by excluding those species where only a single individual was trapped (and could not therefore be in both traps). Of these 2 species were only recorded in the actinic trap and 5 only in the LED. Overall even with the limited data I have it seems that the LED trap is as good at recording the range of species at a site as any other portable trap.
During this Winter I have built 2 more traps, one with 150 LEDs to run off a mains transformer, and the other with 21 LEDs powered from a 5.4v 'portable charger' lithium battery. This second trap I hope will be reasonably effective. The batteries are cheaper and have a greater capacity than the alternative of 8 or more AA batteries and easier to charge, needing only a USB charger. A USB to jack plug output converter is required and a simple voltage boost unit. Both lights are based on the basic design of the 12w lamp. All is needed now is some warm nights to try them out.
I have also come across 2 more papers on LED moth lights, one on a new type of commercial (and currently very expensive) LED lamp, and the other also using LED tape in a different, and slightly odd, way.