It's the wild west out there! About three years ago I wrote a blog post about the Convoy S2+ here on Nature's Rainbows. The FLM collecting community embraced this new high-power LW flashlight and almost every serious hobbyist I know now has one in their toolkit. Over the past three years there have been numerous copycats, "new" higher power flashlights, and dozens of garbage lights - all trying to improve on the original. People making weird patent claims, attempts to design new LED products, and even claims of shortwave flashlights (hint - a viable, true SW flashlight doesn't exist).
When writing my original post 3 years ago I stated my concerns about the heat generated by the UV LED in the Convoy. That little Nichia LED was being driven at 700ma for around 3 watts of power. I knew that was simply too much heat for the very small flashlight body to dissipate. But for $20 who cares! I knew it would last for a while, and the power was simply too good to pass up. As time went on it not only lasted, "higher power" flashlights were introduced, each claiming more than the last. Yet I heard of no fires, no third degree burns, nothing exploding. A few of us informed engineers started scratching our heads. At the power levels claimed, flashlights should be burning up left and right, but they weren't. Why?
I did some digging.
Short story - all lies. The Convoy is barely 2.0 watts on average, some a bit more, many a lot less - REGARDLESS OF CLAIMS OF HIGHER POWER. Are manufacturers intentionally misleading the public? In some cases yes, in others they just don't understand what they are making. Building LED lights is easy - anyone with a little experience can put together an LED light. Designing LED lights is hard - making a product which will work for years, perform as specified, and be reliable, requires engineering capabilities that most tinkerers don't have (I was recently mortified to see an LED "product" one "manufacturer" had put together to sell. It worked, but probably won't work after several hours of use).
So why are Convoy type lights never over 3 watts? The answer is very technical and boring to the average FLM hobbyist. But I will provide some basic facts to explain and the techy can dig further to understand the details:
The Convoy S2 was designed to be a white light flashlight
Many/most white light LEDs operate at 3 volts (appx)
The UV LEDs in the Convoy (Nichia, LG, and others) operate at 4 volts (appx)
The battery (18650) in the Convoy is a 3.7v battery
The driver in all Convoy flashlights is a linear driver (meaning it SUPPOSEDLY supplies 700ma, 1050ma, or 1400ma to the LED). The higher currents supposedly make for the higher wattages. This is where the falsehoods begin. The folks designing these lights either don't know what they are doing, or are intentionally defrauding the public with inflated claims. The problem is that power calculations for these inflated wattage numbers are made based on the voltage of the LED and the driver current (basic ohm's law for power - P=E*I). With a 4 volt battery, driving the LED at 700ma would result in 2.8 watts, 1050ma = 4.2 watts, 1400ma = 5.6 watts. BUT - our batteries are NOT 4 volt batteries. They are 3.7 volt batteries. They may start out at 4 volts (4.2V actually) but very quickly (minutes) drop down to 3.7 volts, and slowly discharge from that point down to 3.0 volts (discharged). As the voltage supplied to the LED drops below its required 4.0 volts, the current drops, thus dropping the LED's wattage significantly.
The charts below show this (actual measurements over several Convoy type flashlights).
The first chart shows the typical discharge curve on an 18650 battery. Note how it starts out a little above 4.0 volts but quickly drops to 3.7 volts - this will vary wildly depending on the type of battery, the current drawn, the temperature, etc. but this chart is a good average.
This second chart shows the actual power of a Convoy type flashlight (an average of several actually tested). As the voltage of the battery decreases the power of the Convoy drops dramatically. At 3.7 volts the LED simply cannot be driven at much more than 1.8 watts. This will vary depending on the tolerances of the driver components, the voltage of the LEDs (a wide range), and the heat generated - but this chart is a good average. It DOES NOT matter what kind of current the manufacturers claims the driver is supplying - under 4.0 volts the driver is not even a factor; it's not even in the picture. The LED is direct driven by the battery (too technical to explain here, but engineers will understand).
Moral of the story? Buy a Convoy. It will last for many years. It is the most powerful 365nm flashlight for the price. But ignore claims of 4 watts, 5 watts, "overdriven", on an on. Those claims are simply not true. There will be variations in the beam pattern depending on the type of LED used, the type of reflector, and the size of the head. But any UV flashlight driven with a 7135 type driver and single 18650 battery simply will not deliver over 3 watts (for more than a few minutes - and if it did, it would burn up).
Side note: There are proper drivers which can be designed to drive a flashlight at the higher voltages required by UV LEDs. I designed my own 9 watt "Convoy type" light and had a blast w/ a couple of them at the most recent Tucson show (2019) - slightly bigger host with lots of heat improvements. A little more expensive than a Convoy, but still nowhere near the price sellers are now hawking their 2 watt (claiming 4W/5W) Convoys for.
