2020 in numbers; LED vs. actinic part 4

During 2020, I have been conducting an experiment to compare a 15W actinic light with a roughly 18W LED light. This was a continuation of something I started in 2019, but this year I have run a more disciplined study. The initial article here has a photo of the LED light - although I've made changes to the configuration, it still looks similar. My update at the end of 2019 is here. I wrote a 2020 half-year update (here) which describes the experimental method I've used in 2020 and some of the changes I made to the LED in April and May; the light hasn't changed since then.

I now present the results for the whole of 2020. Apart from three nights on which I ran a single light, I have run the two lights simultaneously in two different (and non-interfering) parts of the garden. I trapped twice a week, alternating the lights between the two places. The data cover the whole year: I didn't run any traps in my garden for the first three weeks of January, nor for the last 2½ weeks of December, nor for a six-week period covering the second half of July to late August.

In the table above, the "Together" column refers to the two traps combined. The data are only for moths taken at light in my garden and exclude other locations and moths found indoors, etc.

As I wrote in my half-year post, the LED started off performing slightly worse than the actinic striplight. There were two reasons for this: it initially used less power - around 8W - and the UV LEDs weren't very efficient. I changed the configuration in April and early May, since when it has out-performed the actinic light. The full-year data in the table show that it has attracted about 6% more species - particularly micros - and about 30% more individuals. When I look at the period since early May with the improved LED, these figures are strengthened in the period between late spring and early autumn. Since mid-autumn it's harder to see a difference in effectiveness between the lights, but naturally the numbers are much smaller anyhow.

My garden list has grown this year by a deceptively-impressive 205 species (126 macros and 79 micros). However, I only started trapping in the middle of 2018 and my trapping effort in 2020 (number of traps x number of nights) has been four times as much as my total trapping effort before 2020. Consequently I have continued to find the learning curve rather steep, especially as I also trapped in France during the summer and found almost one hundred additional species there. There were 27 species (14 macro, 13 micro) which I found in the garden in 2018 or 2019, but which I haven't seen this year.

New for the garden list:
Spuleria flavicaput
Newton Longville 7th May 2020
(first night with the better LED)

One of the "problems" with a database is the temptation to spend a lot of time slicing the data in different ways. Just for myself, during these dark days I may take a look at the relative numbers of moths found in the two parts of my garden where I run the traps, to see which has the most, and I may see if there are any differences between the effectiveness of the two lights for different families - as I noted above, the LED seems rather more effective amongst micros.

I haven't decided on my plans for 2021. I may experiment with LED vs. LED as I want to try different combinations of wavelengths (colours). Allied to this, I would like to produce a somewhat lower-powered version (around 12W) that I can run off a battery. At home I use mains power, but in theory, during the summer the current 18W version should be able to last all night on my 12V 16Ah battery. However, the nights are too long for the battery before the spring equinox and after the autumn equinox. As I wrote in my mid-year post, heat dissipation is a challenge - specifically the fact that it's produced in such a tiny area - and I have some ideas about how to address this. Finally, the LED light has spent its whole life in part-finished form, held together with elastic bands: this makes it easier to change its configuration, but at some point I should produced a finished version!

Tim Arnold
Newton Longville, Bucks