DIY Moth Light
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above a small selection of moths viewed this summer with the use of a DIY moth light
If you are attracted to seeing ephemeral organisms and like staying up late into the night doing so, moth lighting might be the past time you’ve been looking for. Don’t worry long hikes aren’t necessary, but there is a key piece of equipment that will make your new found sweat-less hobby more fruitful; a moth light. Moths for reasons that still escape me and it seems most Lepidopterists (people that study moths and butterflies) are attracted to lights in the night. Do they think it’s the moon? Do they think it’s a midnight disco? No one seems to have a great explanation, but we do know that different moths seem to have a hankering for different wavelengths (1,2). Most commercially available moth lights use a UV fluorescent bulb or mercury lamp, a large white sheet, and a sizeable battery to power your light. The commercial setups usually run somewhere between 100-$200.
I desired to have a moth light that was cheap, that I could easily put in my backpack for trips into mountains and one that the battery I could use to charge my cell phone. I also hoped to make a variety of lights with discrete wavelengths that might be able to illuminate what moths like which wavelengths with more granularity then we know at this time. Below are the two constructs I have come up with; a 395 nm light and a 365 nm. In a limited number of head to head tests it appears the 395 nm light set up attracts the biggest diversity of moths and lucky for everyone out there, this is the one that doesn’t require any soldering on your part as all of the items are available off of Amazon.
395 nm Moth Light Setup for ~$50. No assembly required!
Parts:
2) RAVPower Portable Charger 10400mAh
or whatever battery charger you like that pumps out at 5V and has at least 5000mAh capacity...allows you to run at least a full night from what I can tell.
3) USB Extension Cable 10ft/3m USB 2.0 Type A Male to A Female Extension
4) white shirt or shower curtain liner
365 nm Moth Light Setup for ~$50. Assembly required.
Parts:
1) 10 Pcs 1W 3W 365nm UV Led Ultraviolet Led Chip Light High Power LED Bead with 20mm Base
2) uxcell 2 Pcs Silver Tone Aluminum Heat Sink Heatsink Cooling 150mm x 20mm x 6mm
3) 4.7 Ohm 1W Flameproof Resistor 10 Pcs.
4) Epoxy
5) RAVPower Portable Charger 10400mAh
or whatever battery charger you like that pumps out at 5V and has at least 5000mAh capacity...allows you to run at least a full night from what I can tell.
6) USB Extension Cable 10ft/3m USB 2.0 Type A Male to A Female Extension
7) A narrow jar (glass) at least 16.5 cm in length
8) white T-shirt or shower curtain liner
Assembly:
You will be making a circuit with 4 LEDs and resistors in parallel. adhere 4 LEDs to your Aluminum heat sink using expoxy equally spaced as seen in the close up image of the assembly and take note of the positive/negative side of the LEDs. Scratching the back of the LEDs and the location where you are to glue them on the heat sink will help to get you a better seal. You don’t need a bunch of expoxy, just a nice thin coat. Epoxy four of the 4.7 Ohm resistors to the heat sink as seen in the photo "wiring layout" below. Dissect one of your USB male to female extension cables by cutting off the male end about 10 cm into the cord. Cut the cord again from this side about 30 cm farther down the cord and pull out the wiring inside, this will be used to wire your circuit together. Trim and solder the wire as seen in "wiring diagram" and "wiring layout" below. Punch a hole about the same diameter as the USB cable into the lid of your jar, right in its center and thread the cable left on your male adapter through this hole. Strip the wires coming from the male adapter and solder them onto you circuit making sure that your positive wire from the male is going to the positive side of your circuit. The best way to test this is just to plug the male USB into a battery and touch the bare wires to your circuit to make sure your lights go on. You now have a functional 365 nm moth light! If you are interested in using a 365 nm light, but don’t want to build your own, contact us info@calnature.org and I can custom build one for the cost of parts and labor.
Wiring layout
Wiring diagram
Functional Test of 395 nm vs 365 nm Moth Lights
On a warm dark September night I found a suitable test location deep in an Oakland park that had two trees evenly spaced where I could hang both lights in close proximity to each other and record what moths and other organisms showed up to each light.
When I hang moth lights I always wrap the USB cord around a branch in addition to the coat-hanger/stick that is supporting the shirt, so just in case a big wind gust comes up that is strong enough to knock off my shirt it doesn’t take the light with it. I’ve also started carrying a few thumbtacks which can be used to pin the shirt to the trunk to stabilize it if there is wind. Below are images of the organisms associated with each light for night. The 395 nm light definitely won in terms of getting a diversity of moths and the showy moths for the night.
I am interested in accumulating data around what moths come to which lights so if you are running your home made moth lights, please think of contributing your data to iNaturalist and using the Observation Field Light Source:395-400 nm LED and Light Source: 365 nm. The benefit will be two fold in that iNaturalist data is accessible to everyone so we all can figure out what moths exist where and when they fly and iNaturalist can use its massive database, artificial intelligence, and a vibrant community of naturalist to help identify your moths.
1. Somers-Yeats, Robin. et al. Shedding Light on moths: shorter wavelengths attract noctuids more then geometirds. Biology Letters. 29 May 2013.DOI: 10.1098/rsbl.2013.0376
2. Langevelde, Frank et al. Effect of spectral composition of artificial light on the attraction of moths. Biological Conservation. 29 June 2011
