I talk with many, many customers both in-person and online about Ultraviolet Flashlights. Most everyone asks me how bright is one UV flashlight compared to another UV flashlight. Or "How far does the beam on that flashlight go?" Not all 365nm Longwave Ultraviolet flashlights are equal. And most importantly, not everybody will be using their flashlight in the same way. Some mineral collectors need a UV flashlight for shopping at Mineral Shows. Some, use them as tools when looking at their mineral collections to find fluorescent minerals they may not realize they had. Many customers take their UV flashlights out into the field.
Over the last couple years the fastest growing population of fluorescent mineral collectors is probably surrounding Lake Superior in Michigan and adjacent states. An ever increasing number of collectors are hitting the beaches looking for glacial, rounded Sodalite rich Syenite, known as Yooperlites, Emberlites or other locally coined names. Different attractive patterns of specks, blebs or bands of Sodalite in the rock glow in various intensities of orange color under 365nm UV light.
Certainly, the number of LEDs in a light, LED output, reflector quality and shape, battery voltage and numerous other variables factor into what makes one light more useful than another. When comparing flashlights, one of the biggest factors defining the useful distance of the flashlight is rarely talked about. What minerals you are collecting? The human eye detects certain colors in dark environments better than others. Willemite from Franklin, New Jersey glows an intense green under shortwave ultraviolet light. But some of the material responds almost as bright under longwave UV as well. Canadian Wernerite and Greenland Sodalite are some of the brightest longwave minerals on the planet! Some of the latest high power UV LED flashlights will allow your eyes to find this material starting at around 80-100 feet away. But that is NOT always the case with most other longwave UV reacting minerals. Fluorescent minerals from different localities react differently. Some localities produce solid masses of minerals where others may have crystals in a non-fluorescent matrix. The richness of the piece would define how bright the rock reacts to UV. On average, much of the Sodalite I have seen from Lake Superior areas is a varying mix of fluorescent Sodalite to non-fluorescent Syenite. Certainly there are super-rich pieces found. But there are plenty which are not. And I have seen rows of 5-gallon buckets of this rock.
I have conducted some "rough" observations of a number of UV flashlights in order to present a comparison for you. UV radiance measurements were taken at 2 foot intervals starting at 20 feet from my UVX radiometer 365nm sensor and decreasing down to 2 feet. I left each light on for a few minutes to let voltage drop a bit and then conducted some quick range measurements. As you see in the graph below, the numbers follow the Inverse Square law. It states that when you double the distance away from the source, the light will be 1/4th the intensity at the original distance. When you move the light triple the distance away, the light will be 1/9th the intensity. Four times, 1/16th. As you can see by the numbers, light intensity drops off pretty quickly. The numbers on the left of the graph are in mW/cm2. The scale on the bottom is the number of feet from the UV radiometer the measurements were taken. It should be noted that I was going to try to see how one of the common 21-LED 395nm Unfiltered UV flashlights would perform. But as expected, this quality UV radiometer sensor completely ignored the wavelength of light coming out of it. Putting it right on the sensor may have read 0.01 mW/cm2. I wrote this article in January, 2020. Since that time, I have had my UVA Radiometer factory calibrated. So the actual numbers in mW/cm2 are higher than the scale on the left side of this graph. Relative strength as you see compared in the graph is the same. I will be re-measuring a number of lights in the future with the calibrated meter. But for now, please excuse the uncalibrated readings on the left.
Later I put a pretty rich Yooperlite next to the meter, walked further back and then found the distance when I started seeing the specimen. There was a street light about 75 feet behind me. My porch light was on. So I did have some distracting ambient light like you may experience either toward dusk or if there is moonlight when you collect. I then pointed the light directly at the sensor to try to determine what UV radiance seems to be needed to find these Great Lakes Sodalites. I found this to be around 0.25 mW/cm2.
So how close do you need to be to easily find the average Lake Superior Sodalite when there is some ambient light, but pretty dark?
Approx 4 Feet #6: Convoy S2+ Nichia
Approx 6 -7 Feet
#3: UltraFire UF-1408 (3-LED)
Approx 10 Feet
#2: UltraFire UF-21 (5-LED)
Approx 12 Feet
So the clear winner here is the Way Too Cool C8. Trailing behind is the UF-21. Then the two Convoy S2 flashlights and the UV-1408 are all pretty close. Last, but not least, in this list is the old original Convoy S2+. A very good light. It just doesn't hold a candle to all the new lights. The Convoy C8 accomplishes this with a better driver and just a single UV LED. The UltraFire lights have to burn 3 and 5 LEDS and aren't quite as powerful. They did a good job leapfrogging the Convoy S2 products at the time. But they are no longer give you the longest searching distance.
This article compared a handful of lights. There are plenty of others on the market. It was created in response to the many customers asking me "How far away can I see Yooperlites?" I give conservative distances. There are so many variables that can affect the distance. Different people have different vision (young vs old). We all use different batteries. Outside temperature may be a a factor. I tested everything on a 28 degree evening. The idea was to provide a basic ranking of some popular lights.