(work in progress....)
Just a few years ago my feeling was that we would not see SW flashlights "in my lifetime". I was so wrong. They are here, and here to stay. Several manufacturers are shipping both MW and SW flashlights in various configurations. I no longer make lights for public consumption but have built several of my own for testing (and for my daughter).
I am simply in love with these lights. They offer many advantages over the portable fluorescent tube lights (FTLs) that have been the mainstay of our hobby for decades:
(NOTE: I'm using "FTL" as an abbreviation for the old technology fluorescent tube lights we are all used to)
Small, fit in your pocket, with integral rechargeable batteries.
Intense, focused spot which lights up even the dimmest of fluorescents.
Really handy to use at shows for quick checks
MW is revealing fluorescence that we have not readily observed before, just as the Convoys did for LW
Eliminates the complex, bulky external batteries our TLs use.
Both 310nm and 255nm available.
But, as with all new technology, there are things that new buyers should be aware of, especially when comparing to FTLs (fluorescent tube lights). Most importantly - these are new, very new. We've only had a few months of testing and learning. There are sure to be new developments on the horizon, new components, bugs, etc. This is just the beginning of an exciting time.
So how do the new shortwave and midwave flashlights differ from a portable fluorescent tube light (FTL)?
Power and Beam Spread - Spot vs. Flood
The little LEDs produce a surprisingly intense spot beam. When measured with a UV meter they actually produce a brighter spot than tube based lights (which are only flood). But this is where the difference comes in - flood vs. spot. This intense spotlight beam from the flashlights results in producing some amazing fluorescent responses, but only over a very small circle compared to flood FTLs. A person accustomed to exploring a tailings pile or mine dump with a flood TL will at first find the small spotlight beam limiting. FTLs cover a wide area, allowing you to spot "glowers" even in your peripheral vision. But I personally prefer the brighter spot of the flashlight. The intense spot is going to take some getting used to, but the small form factor and intensity makes them fully worth the adjustment.
Power Measurements - Spot 255nm (SW)
The images below (courtesy Wim Bruines, ColorGems) depict the beam power when measured as a spot. The 1st image shows a 35W FTL (fluorescent tube light) one foot away from a UVC meter. It reads 134uW/cm2. The 2nd image shows a single LED flashlight, same distance, with a reading of 914uW/cm2. The 3rd image shows a quad LED flashlight with a reading of 1418uW/cm2!!! That's over ten times the output of the FTL flood in the 1st image. Clearly the spot is much more intense with SW flashlights, and even more dramatic with MW flashlgihts.
Power Measurements - Flood
It is very important to understand that a typical UV flashlight is a spot device. The intensity is determined by the focus of the spot. A FTL light is a flood light and will evenly light up a broad area, but at much less power than a flashlight. The image on the left shows an FTL light illuminating two meters equally at the sides - 115uW/cm2. If a third meter was placed in the center it would read approximately the same - an even flood light. The image on the right shows the same setup with a flashlight; the meters out of the spot show only 20uW/cm2. If a third meter was placed in the center of the spot from the flashlight it would read a whopping 1418uW/cm2 - an intense spot light.
Pure 255nm/310nm vs. Broader Output from TL
There are two different wavelength flashlights available from our manufacturers today for our hobby - 255nm peak (SW) and 310nm peak (MW). Both exhibit a very tight output with very little "spill" above/below their peak output. This is different than the output of FTLs. Fluorescent tubes peak at 254.3nm (or 302/312/315nm for MW). But the "curve" is much broader, generating UV, at various levels, in other UV bands. The chart below compares various UV LED intensities to a 254nm FTL. (Note: this graph is temporary. It's a good example of LW LEDs vs mercury tubes but does not have SW LEDs on it. Will update when I get home).
(For example only, needs to be revised)
This very tight output, peaking at 255nm (or 310nm), results in different responses from our minerals compared to what we are used to. Some minerals need that "spill" from FTLs to fluoresce - they are more reactive to the broader band SW UVC, perhaps 265nm or 240nm. Examples shown below. But some react strongly to the intense 255nm peak resulting in a brighter response.
R&D in this area is focused on producing a cost-effective multi-wavelength flashlight, better mimicking the responses seen using FTLs. Some combination of UVA, UVB, and UVC LEDs with appropriate power levels will offer up a great replacement for the broader band FTL.
Midwave - Until now the ugly stepchild
I need to make special mention of the 310nm flashlights - they are as important an innovation for our hobby as the original Convoy S2 was. When folks first started using that light they were amazed to find minerals fluorescing that they didn't know were fluorescent under LW. The intense spot revealed fluorescence where a FTL could not. Same story with the new MW flashlights. As I explore our inventory of rocks I'm amazed at the finds I'm making. As many know, my area of specialty is Greenland. One very elusive mineral we were always looking for was leucophanite. Scarce as hen's teeth. But while on vacation visiting my Granddaughter I browsed my daughter's inventory. Much to my surprise we found several major specimens of this mineral, all because of my MW flashlight (leucophanite fluoresces strongest under MW). This light has prompted me to build a MW only display cabinet to show off the many new finds I've made just in my inventory.
Leucophanite (violet) with unknowns, MW
SW and MW are very inefficient. This means they consume a lot of power just to generate UV. For example, a single 255nm LED consumes (700ma*6v) 4.2W of power. It only produces 100mw (milliwatt) of UVC. But even this low power, when focused to a tight spot, is far brighter than a FTL. 4 watts of power is reasonably handled by a well designed flashlight. It will get hot but nothing to worry about. Periods of cooling are recommended.
The more powerful flashlights use a 4-die LED (4X the power of a single LED). These will consume 17W of power, but is spec'd at 500mw of UVC. 17 watts is a lot of power for a flashlight body to dissipate. Current designs have a proprietary method to handle this heat generation. (The MW flashlights are more efficient, 170mw and 550mw of UVB.)
A good practice is to allow your flashlight to cool frequently - this goes for any UV LED flashlight, 365nm, 255nm, or 310nm. Heat is an LED's enemy. The cooler we run them the longer they will last.
Old FTLs hate to be power cycled. Turning the power on is the most damaging thing you can do to a fluorescent tube. The act of firing (lighting) the tube blackens the ends, and if done frequently, can even blow out a tube. But hobbyists do it anyway, mostly to conserve battery power. If left off for a few minutes it can take up to four minutes for the tube to reach its full brightness again - all FTLs need to warm up.
An LED flashlight does not have this problem. There is no voltage surge and the light can be powered off at will, as frequently as desired. This both conserves battery power and reduces heat in the flashlight.
Single LED SW/MW flashlights use a standard 21700 battery but 18650s (as used in the 365nm Convoys) will fit. Quad LED lights use a 26650 battery. Due to the current needed to drive the quad an unprotected cell is recommended. Always keep the cells fully charged; this places less load on the electronics of the flashlight.
Current models cost around $140 for the single LED version to $350 for the quad LED unit. This compares nicely to portable FTL lights that cost $275 and up. Keep in mind that they are two different animals - a spot vs. a flood. You must adjust your expectations accordingly. Given a choice (and a big budget) I would go with a good FTL for searching large areas efficiently and a flashlight for close examinations, at shows, and as a handy everyday carry light.