At the end of 2019 I made another post (here) with a progress report. As we are now half-way through 2020, I thought I would give a further update. In 2019 I was running a single trap, alternating between LED and actinic lights on different nights. Variations in weather and moon between "actinic" nights and "LED" nights made comparison rather difficult. At the end of the year, I worked out how (i.e. where!) I could run two traps in the garden simultaneously, so I bought another identical trap, spent the first three weeks of January on maintenance and for all of 2020 I have run them in parallel. I have tried to operate the traps twice per week in order to get enough data for comparison, and as there is a difference between the two trapping sites, I alternate the lights between the two locations. During 2020 I have made some other changes, which I'll mention shortly.
The results for these last six months as a whole are below:
|2020 H1 Results||Actinic||LED||Overall|
|Best night for species||23-Jun||23-Jun||23-Jun|
|Species on best night||47||46||73|
|Best night for moths||23-Jun||15-Jun||23-Jun|
|Individuals on best night||233||211||392|
|Total number of moths caught||1136||1449||2585|
I then found that the UV LEDs were extremely inefficient: this is a common problem at UV wavelengths, but hard to identify because most datasheets do not show the radiation flux (ϕe) that they emit. Only about 2% of the electrical energy was being converted to light and the rest was coming out as heat. After more research, I identified a source of UV LEDs that are about fourteen times as efficient, so in May I replaced six of the LEDs with these better versions. Heat dissipation is still a problem and I am limiting the current so as to keep chip temperatures below a conservative 70°C, meaning that the total power to the LEDs is just under 20W (the drivers consume another 2W).
These changes have made quite a striking impact on the relative performance, best illustrated by the cumulative number of moths caught. Since making the changes, the LED light catches about 35% more moths and 13% more species than the actinic.
|7 May 2020 onwards||Actinic||LED||Overall|
|Total species caught…||127||144||182|
|… of which macros||81||93||112|
|… of which micros||46||51||70|
|Total moths caught…||934||1275||2209|
|… of which macros||605||909||1514|
|… of which micros||329||366||695|
I will continue this experiment for the rest of the year. I may make more changes to the LEDs, but when I think I have finalised the configuration, I will then look to improve the bonding so as to be able to run at a higher power: better bonding generally means it's harder to swap LEDs. I will probably also produce a new set of drivers that will power a subset of the LEDs at a lower current, in order to restore the option for compatibility with running off a battery. Finally, when I am no longer taking the light to bits to change components, I will use a less Heath-Robinson (pun acknowledged) way of mounting the light on the trap, and add baffles - but that might be a job for 2021.
Newton Longville, Bucks