UV Flashlights - Outlandish Claims of Power
I’m really getting tired of all the BS out there. Chinese vendors make outlandish claims about their flashlights and non-technical vendors here in the USA buy them, then pass those claims onto unsuspecting people in our hobby. It borders on criminal.
First some basics:
These lights are not what they claim. In China it is a sport to lie and exaggerate. This is not a racial statement, it is a cultural statement; I was raised in a Chinese household. Lying and misrepresenting products is a sport in China. Don’t believe me? Just google it, tons of research, one for example: Illogical or tactile? Lies in Chinese Culture
At powers claimed by vendors, your flashlight would get really hot. When does human skin feel pain from a burn? 111f (hot bathwater) you begin to feel pain. At 118f human skin can sustain a first-degree burn. At 131f you can get second-degree burns.
Watts are not a meaningful measure for the intensity of LEDs, nor are lumens and LUX as these only apply to visible light LEDs. The UV industry uses radiant intensity as a measure of the intensity/power of a UV light source.
Several of our most popular vendors make these fraudulent claims, smiling all the way to the bank (or maybe just not knowledgeable in tech, in which case they should not qualifying lights for sale).
I have tried over many years to educate our vendors on this topic, but it seems to fall on deaf ears, or they just don’t want to learn. It’s shameful.
But… Proof is in the pudding, right? I developed a simple test to show how hot your flashlight would get if the claims of power were true. I wrapped a strand of nichrome wire (the kind of wire that glows in your toaster) around the head of two popular flashlights, a Convoy S2 type and a soda-can type. These heavy aluminum heads are designed to soak up the heat generated by the LEDs so they won’t burn out. The wires heats up the head of the flashlight just like an LED would, giving a rough approximation of how much an LED would heat up the head at various wattages. The heat the wire generates is controlled by the wattage applied.
“80W” Soda-can style shown on the left, “10W” Convoy S2 on the right. Gray smudge is heatsink compound to insure good heat transfer to the temperature probe. Weight at the bottom is to take up slack as the heated wire expands.
I then applied voltage using my adjustable power supply to the wire and adjusted the wattage (79.8W in this pic) in various steps to simulate the heat generated by the LEDs. Using my handy meat thermometer I monitored the temperature at various wattage increments.
I show the results below in a table. BUT – keep in mind that these results are meaningless. Watts have nothing to do with the power of the LED, even if the flashlight is too hot to hold. Only radiant output matters. But it’s complicated to measure the radiant power being produced by our flashlights. Manufacturers must have special equipment to measure radiance, and the average user has no way to tell if their specifications are real or BS.
The best advice I can give is to buy from a vendor who has a technical background and is trusted in the community.
Ask for recommendations from folks in the Facebook group. Compare any new light to a known light for brightness. If the light isn’t too hot to hold, it ain’t 15 watts, 20 watts, 60 watts, or 80 watts (3rd degree burn territory – ever touch a 75W incandescent light bulb? That runs about 229f! You wouldn’t even be able to touch a 30 watt light bulb (I dare you, try!).
Technical stuff: So how do these light manufacturers make these claims?
In the case of the smaller lights (S2 types) they just lie. They tell you the wattage at the start of the battery’s voltage (4.2v) which quickly drops to the run voltage of 3.7v, dropping the wattage, even more as the battery discharges. But even then, they get too hot. Note many of the sellers admonitions to turn the light off when it gets hot.
In the case of the big soda-can style lights they are much more nefarious. I hooked up my oscilloscope and power meter and tested 80 watt lights from two different vendors. Each started out at 36w (not the 80w claimed – that’s an outright lie) but they quickly started automatically ramping the power down in the first few seconds (called stepless dimming, you don’t notice it). They were nicely bright to begin with but within 5 minutes they were both running at less than 7 watts. The interesting thing to note is that the human eye doesn’t really notice this dimming unless you are monitoring it closely.
Convoy S2 Type, Claimed to be 10 Watts
Power – Temperature
3 watts – 113f
5 watts – 129f (first degree burn territory)
6 watts – 145.8f (second-degree burn)
10 watts – 186f
15 watts – 248f
20 watts – 297f (wires glowing red)
Get the point?
Soda-Can Type Light, 4 Batteries, 4 “quad-core” LEDs, Claimed to be 80 Watts
Power – Temperature
10 watts – 87.4f
15 watts – 95f
20 watts – 145.8f (second-degree burn)
30 watts – 186f
60 watts – 248f
80 watts – 297f (wires glowing red) (reaches this temperature in 5 minutes from a cold start)
Get the point?