Sunday 15 December 2019

2019 review, LED vs. actinic pt. 2

A week ago, Dave posted his annual review of what he had caught in his garden. I'm just finalising my records before sending them in, so I thought I would do something similar. Since early July, I've been alternating the light I've used between a 15W actinic strip and a 13W LED light that I designed and constructed myself, so I have also broken down the figures by the type of light I've used. I've carried out a similar analysis to Dave, apart from the additional breakdown between actinic and LED light and the absence of a comparison with previous years because this is my first full year of mothing. Here are the results for the year, with apologies for some small formatting issues that aren't in my Excel originals, but which appear when I paste the tables into Blogger:

2019 Results
Actinic
LED
Total
Nights run
25
13
38
Of which nights run before July
12
0
Species caught
143
117
182
Macro species
102
82
127
Micro species
41
35
55
Best night for species
25-Aug
27-Aug
Species on best night
47
59
Best night for moths
25-Aug
10-Jul
Individuals on best night
351
594
Total number of moths caught
1569
1831
3400

Highest total counts for a species
Actinic
LED
Macros
135
302
Heart & Dart
Square-spot Rustic
Micros
97
427
Agriphila geniculea
Chrysoteuchia culmella
The figures above only cover moths caught at home, in the trap. They exclude 43 moths found indoors, attracted to a lighted window, etc. The figures also exclude other sites. The total number of species caught is less than the figures for LED and Actinic light added together, because many species have been caught by both lights.

As I only started to use an LED light in July, I performed a separate analysis of the second half of the year, when I've been alternating the two kinds of light - in a previous post, I mentioned that I don't run the two lights on the same night, and on many occasions weather conditions & lunar phase haven't been comparable from night to night. However, it's probably OK to compare them in aggregate. Here are the figures starting from July, when I began alternating the two light sources:

July 2019 onwards
Actinic
LED
Total
Nights run
13
13
26
Total species caught…
120
117
162
… of which macros
81
82
108
… of which micros
39
35
54
Total moths caught…
1238
1831
3069
… of which macros
928
1153
2081
… of which micros
310
678
988
I had a feeling that although they seem to be catching similar numbers of species, they might not be catching the same species. In fact, this is quite striking: of the 108 species of macro moth caught since July, only half of them (55 spp.) were caught by both lights: the actinic got 26 species that the LED didn't, and there were 27 moths caught by the LED and not by the actinic.  For micros, the figures are even more striking: 54 spp. overall, 20 by both lights, 19 actinic-only, 15 LED-only.

So I deepened the analysis to see if there was a pattern. I'm still working on this, but it would appear that there is no pattern related to families or to sub-families.  As an example, the actinic "missed" three species of Ennominae that the LED caught (including Canary-shouldered Thorn and Willow Beauty), but the LED "missed" five species in that same sub-family which the actinic caught (including Dusky Thorn and Mottled Beauty). Flight periods shouldn't be much of a factor, since I nearly always manage to run the trap with the two different lights within a week of each other.

What do I conclude? There's not much difference between the two lights, at least in terms of the numbers of species caught. I'll continue this next year to see if any pattern emerges about which light is better with specific species, but I suspect that this could be fairly random.  The LED did catch more individual moths, although in the case of the micros, this is largely down to one night with a huge number of Chrysoteuchia culmella coming in from the field 3 metres away.

Tim Arnold
Newton Longville, Bucks

2 comments:

  1. Hello Tim,

    A very interesting set of figures and it does begin to look as though LEDs will eventually be the way forward when those of us who use MV traps have run out of 125wt bulbs. If you have the time and enthusiasm for it, it would be good to see a full year comparison between your two types of light in 2020.

    Of course, now that we're leaving the EU, I wonder if that directive which ended the manufacture of mercury vapour bulbs will no longer apply. Depends upon how much "alignment" we'll still have with EU regulations, I suppose, but maybe a niche market will open up if an entrepreneur is willing to take it on!

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  2. I certainly intend to continue the comparison for all of 2020. I have read quite a lot of papers around the subject of moth lights. One thing I have learned is that the radius within which a light is effective is probably significantly less than I thought - about 20m to 30m. That means that I can probably run two traps simultaneously, which will remove some of the unwanted variables making direct comparison more difficult.

    Now all I need is a second trap. Dear Santa, ...

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