11 Jul 2024
A series of notes to update the previous posts on this subject.
While most of the content of my two previous posts on this subject are still valid some changes have happened over the last few years. The main one is that 5.4v uV LEDs have become available that can be powered directly from a USB output. They appear identical to the 12v ones and can be used in exactly the same way, but setting up and powering a small light-weight trap has become simpler.
So I no longer use the small lamps with a few LEDs powered by 4 AA batteries via a voltage regulator. Instead I use a lamp with 21 5.4v LEDs plugged directly into a 20000 mAh Lithium battery, the type sold as a portable phone charger or power bank. These cost much the same as 4 2500 mAh AA Eneloop batteries but are easy to charge and just as portable. The 20000 mAh battery powers the lamp for 1 or 2 nights, bigger capacities are available but are larger and heavier and take longer to recharge. It may be possible to run more than 21 LEDs from the battery but I havn’t tried it (see below), it would require some experimentation as well as checking the suitability of the cables and other components.
I still use the lamps with around 60 LEDs powered by a small 12v 7.2 Ah torch or motorcycle type battery when absolute portability doesn’t matter, and if mains power is available one with 150 LEDs powered by a 12v transformer.
When buying LED tape of either voltage make sure you use the 5050 type with 60 LEDs per metre, others are not as bright, or have the LEDs spread out more on the tape.
As I found out early on ultra-violet LEDs require more power than visible light ones so it is not possible to power a whole reel of 300 LEDs from a transformer. Please note almost all the sales descriptions and data sheets for uV LEDs do not mention this, these seem to be generic for visible light LEDs which have much lower power requirements.
I still have not found a completely accurate data sheet for the 5050 uV LEDs but they seem to draw around 0.24 Watts for each LED. White light LEDs are usually rated as 0.05W each.
Some adverts appear to suggest that a reel of 300 12v uV LEDs can be powered by a 60W power supply or 200 5.4v uV LEDs can be plugged straight into a USB socket in a phone charger or similar. You can’t without creating a possible fire hazard so don’t.
Trying to make a lamp with more than 150 of the 12v uV LEDs makes everything get very hot, and the voltage drop at the end of the series produces dimmed light and no net gain. Even 150 LEDs together can get hot enough to melt the glue on the tape unless some means of dissipating the heat is introduced. I use a length of thin walled aluminium tubing about 50mm in diameter to support the lights which seems to work well.
Don’t buy the waterproof silicon-covered tape, the silicon goes opaque very quickly. And because the visible light output is low anyway this is not apparent, close examination will show an area of opaqueness above each LED effectively blocking most of the output.
Do take care not to look for long at the lamp when the LEDs are switched on, because although they emit little visible light and seem dim the uV output is high and could be dangerous.
My traps are only one way of making your own portable traps and there are an increasing number of ideas out there, as well as a number of commercial LED lamps and the traps to go with them. So whatever your budget or DIY skill level a way of trapping and recording moths can be found to suit everyone.