Photon Microlight III Violet/UV

Photon 3 (Violet), retail $25 (
Last update: 02-27-03

Photon 3

This is the latest incarnation of the popular, all-digital Photon 3 Microlight, from LRI. The sample I'm testing today is equipped with a high powered near-UV LED and all-new logic, and as such will be treated as an entirely new product.


The new version Photon 3 comes with batteries already installed, leaving you only to pop off the back and remove the insulator from inside the battery compartment. This clear plastic tab type insulator is there to ensure the light arrives on your doorstep with the freshest batteries possible.
Instructions on the retail package remind you to pull the insulating tab if you don't see or feel it sticking out the side of the flashlight when you first get it. :)

To get a quick shot of deep violet light anytime, just squeeze the button towards the front of the light's casing. The rear button is tied to the microcontroller inside, and does all the real work. When you press and hold down the rear button, the Photon 3 cycles through all of its modes: Auto Off, High Brightness, Medium Brightness, Low Brightness, Fast Strobe, Medium Blink, and S.O.S. signal.
The strobe modes aren't true strobes because the "on" time is relatively long, so you can probably forget about trying to do true stop-action effects - however you can stop or reverse an electric fan or other fast-moving object with the light's Low mode because the "on" time for the LED is really short in this mode.

While the rear button is being held, the light will keep each mode on for approximately 2 seconds (contrast this with the earlier P3 version), then move on to the next. To stop at a mode you want, just release the button. The next time you press it, the light turns off, but it "remembers" the last mode that was on, and activates it the next time you use the light by pressing the rear button.

To get the maximum output on demand, just press the top button anytime; it immediately overrides the microcontroller and gives full power regardless of the light's previous setting. This button is momentary only, so you have to hold it down for as long as you need the full brightness; once you release it the light returns to the mode you used last, or turns off if it was already off to begin with.

The light comes equipped with a small tail ring & large sturdy chrome keyring for quick & easy attachment to your keys; you may also remove the keyring and affix the Photon 3 to to lanyards, clips, or other attachment accessories of your choice.

Unlike the Photon 2, changing the batteries in the Photon 3 is a tool-free and screw-free process.

No tools battery change

Just turn the light upside down, and carefully pry the battery cap off by inserting a ballpoint pen or the tip of a nail file under the tab; then pulling the cap off once the tab is lifted far enough for you to grasp.

Remove the two dead batteries and discard. Insert two new batteries, button-side facing down, in the battery tray. The first battery to go in will go straight to the floor of the battery tray; slide the second battery in right on top, being sure it goes under the metal retainer. Then pop the lid back on by aligning the tab with the notch in the flashlight body, and press it into place like a Tupperware lid. Be sure the lid is flush with the flashlight body.

More than ever, it is important that you get the batteries in correctly the first time around. With just an LED, you can sometimes get away with it, but with a true microcontroller at the wheel, something nasty might happen if you put the batteries in backwards.

Current usage at standby (light "off") was measured at just a couple of microamps - this will not affect battery life, yet is enough to maintain the light's internal memory. Nice circuit. :)

Like its predecessors, the Photon 3 is one tough cookie. The housing is made of a glass reinforced polyurethane compound, and is, for all intents and purposes, indestructible. The LED is surrounded on its sides by a black plastic grommet, and the light is supposed to be submergible to at least several feet. This sample is so new it did not yet have an instruction card or packaging, but I expect it to be physically identical to the last version of the P3, and as such it should be water resistant and capable of withstanding the accidental drowning in a puddle or slush pile.

The only real construction fault I can find (this goes for all Photon models) is lack of protection for the LED; after being dropped a lot or spending a lot of time in a pants pocket with change & keys, the LED's finish will become marred. The LED has been known to break in a head-first fall, but this probably doesn't happen very often and I honestly wouldn't worry about it. In the unlikely event you do manage to end up with a broken LED, LRI will replace it.

The purple LED Photon 3 has a number of different modes programmed into it.

Auto Off is just that. When the light is left on in this mode, it shuts itself off after 1 minute and 15 seconds, signalling activation with a 1-second smooth ramp-up or "soft start", and signalling deactivation with several seconds of half-intensity operation. See test notes below for info on the deactivation sequence.

High mode is the light's high brightness setting.

Medium mode dims the LED considerably.

Low mode dims it way down; this is useful for situations where absolute maximum battery life is a necessity. The on-time for the LED in this mode is very short, and it can be used as a stroboscope in this mode. It is able to produce true stop motion strobe effects in moving objects like motors & rotating fan blades.

Fast strobe causes the light to blink around 8 times a second; this might be useful in party or rave situations, and may enhance the UV effect in objects where this fluorescence is marginal at best. The on-time for the LEDs is too long to be a true strobe, but this mode is attention grabbing nonetheless.

Medium strobe blinks around 3 times a second. These are long blinks, like a car blinker gone mad; not short strobe-like flashes.

S.O.S. mode is a mode where the flashlight automatically signals the international distress signal (3 long blinks, 3 short blinks, and 3 more long blinks followed by a long pause); though in the UV version of the P3 this function may be of limited value. Remember, this light comes in other colors too, including white. That's where the S.O.S. signal would be more usable. The light will continue to flash S.O.S. until it is turned off, the mode is changed, or the batteries poop out.

From any of these modes, pressing the front button will override the mode and shine the LED at its maximum intensity; this mode is even about 5% brighter than High mode. It will continue to light in override mode for as long as you hold the button in; and will return to the last used mode (or off, if you started with the light turned off) as soon as you release the button.

beams from Photon Micro Lights
Photon 3 in near-UV on the test target.
Wavelength is too short for my equipment to measure.

The LED in the new purple P3 appears to use a Cree designed chip, and outputs at a wavelength of between 401 and 403nm. While this is a bit on the long side, it is still well within the "useful" range for doing basic fluorescence checking - currency, club hand stamps, looking for scorpions, and that sort of thing. If the wavelength were shorter, the light would appear much dimmer, and if it were longer, it would appear blue (instead of purple) and would no longer activate the anti-counterfeiting devices in US currency; though other fluorescent & day glow articles would still glow. The people at LRI decided upon a wavelength range that would result in good visible brightness and good fluorescence characteristics at the same time. Light within a range of wavelengths between 397nm and 404nm satisfies these requirements.

The dish on the new purple Photon 3
As with the previous incarnation of the Photon 3, here's an idea of what to do with all the modes. (NOTE: Not all ideas listed here apply to the violet P3, but do for white and other bright colors)

BRIGHT: When you need the brightest possible light you can get out of a single LED, choose this mode. With the purple P3, objects will fluoresce from 15 to 20 feet away, and marginally fluorescence will be more easily distinguishable in higher ambient lighting when you set the P3 to this mode.

MEDIUM: This mode is useful when high brightness is just a bit of overkill. Most fluorescent materials will glow just fine with this intensity setting; and your batteries will last noticeably longer.

LOW: This is the perfect mode to use after your eyes have become accustomed to darkness. At this level and LED duty cycle, the near-UV output isn't damaging to the eyes of those around you and you'll get a nifty dotted strobe-like effect if you whirl it around on a lanyard. Battery life should be longer than any of the other modes. Low mode can also be useful in emergency situations where batteries might be hard to come by for awhile.

FAST BLINK: Use this mode for short range signalling & locating, and for highlighting fluorescence in objects where this glow is already marginal. Put this on the top of your tent door and you'll never stumble into the wrong tent ever again. Kite flyers also want something eye-catching to attach to their kite, and something like this *would* catch the eye. Having several Photon III's in different colors (including purple), all set to fast blink and attached to a kite might end up garnering a few extra calls to the UFO reporting center.

MEDIUM BLINK: This mode can be used much like Fast Blink, but the blink rate is substantially slower and the LED stays on longer. Another option for signalling & hobbies; this one is also useful for bicyclers & scooter riders who want to be seen and want to be unique with their choice of LED color, but don't want to give someone a seizure. A bit of Velcro on the handlebars and on the back of the light will affix it to your vehicle, yet leave it easy to remove & take with you to help prevent theft when your bike or scooter is left unattended.

S.O.S. This is the international distress signal. While it's usefullness in a near UV light may be limited, remember the P3 comes in white and assorted brilliant colors too, and in those units this signal will be bright enough to be seen by nearby rescuers; this is a nice feature especially if you become injured or can't scream for help but see rescuers going past you in the woods. Granted, you may never actually have to *use* this mode, however it's good to know it's there if you ever need it.

AUTO OFF: Do you always forget to turn flashlights off, only to come back later and find they're full of dead batteries? Then this mode is for you. An idea the inventor himself suggested is to stick a Photon III on the wall in a hallway or small room you often pass through after dark; just give it a little press and the hall is lit up for you without having to fumble with the lightswitch or get blinded by rows of 100W bulbs in the ceiling; and you never have to remember to turn it off.
Vacationers can stick one of these on the hotel nightstand or bathroom basin and use it the same way - give it a little press, have light long enough to pass through the darkened area(s) and never worry about shutting it off.

UPDATE 04-18-02:
This sample incorporates new logic that is to be installed in all future Photon 3 colors. Here are the primary differences I've found between this logic and the logic in older P3s:
  • Mode change time reduced from 4 seconds to 2 seconds.
  • The annoying blinking in Auto Off mode has been replaced with a "soft start" (ramp up) at initation, and a brief period of half-intensity at termination. The termination sequence may actually include a battery test mode; but I cannot verify this until I have run down the batteries in the test sample.
  • Auto Off on-time has been extended to 1 minute 15 seconds.
  • All new Photon 3 units now use dedicated microswitches instead of a less reliable leaf switch.
  • All new Photon 3 units also have a redesigned battery retainer; this holds the batteries in place even if the battery lid comes off.
  • The "slow blink" mode has been replaced with an automated S.O.S. distress signal.
  • Modes can now be changed regardless of whether you start with the light off or on.

IMPORTANT: Because this light emits energy right at the border between visible and UV, it should be treated like a high intensity UV source. Do not stare directly at the LED when it is on. Intense UV light can cause eye damage. A label is affixed to the back of this light to remind you of this.

UV warning label

UPDATE 02-27-04:
Today, I received the new "Hands Free Photon Clip" directly from LRI. This simple device allows you to use your Photon light hands-free; clipping to the brim of a hat or to a shirt pocket or even to your collar if your shirt does not have a pocket. You can also clip it to the bridge or lens of your eyeglasses if you wish. The fairly stiff spring-loaded clip has serrated "teeth" on the inner faces of the clip, so it ought to stay put where you clip it on. A ball & socket joint on a pedestal allows the flashlight to be pointed just about anywhere when it's affixed to the clip. There were no instructions provided with my evaluation sample, but I think it's intuitive enough that you probably won't need them.

In case you can't figure it out though, it kinda goes like this:

Insert the front (LED-end) of your Photon Micro Light into the front of the clip where the two larger and more widely-spaced plastic tits are. After the front of your flashlight is in there, lower the rear side of the flashlight (where the keychain hole is) into the two narrowly-spaced plastic tits on the Hands Free clip. Be sure it's on there all the way so you don't lose your Photon light. Clip it to whatever you want to clip it to. Turn your Photon on, and aim it wherever you need the light. Finally, turn your Photon off, at least until you're ready to use it.
There, that was easy, wasn't it?

Here's the device itself, compared in size to a Photon 3.

And here it is, clipped to the brim of a baseball hat.

And, finally, here it is clipped to a pair of eyeglasses, while I'm using them.
My eyes are closed in this photograph because one of them is still {vulgar term for having had intercourse} up from (crash course in) brain surgery I had in late 2002.

The Hands Free Photon Clip costs $4.95, but is included free of charge if you buy a Photon II or Photon 3 from LRI's website by 03-15-04.

Updates to this page will occur as needed.

Improved programming over original P3
Good output in HIGH mode
Durable construction
Slightly wider beam than most other UV LED lights
Tiny in size
Much more durable than other UV LED lights
Easy to carry & store
Better water resistance than the original Photon 2
Screw-free battery changing
No plastic switch to fumble with, leak, or break off.


Wavelength of UV model is just a hair on the longish side.
Batteries can be expensive & hard to find in an emergency.

    PRODUCT TYPE: Mini keychain UV flashlight
    LAMP TYPE: LED, 5mm, ~400nm near-UV
    No. OF LAMPS: 1
    BEAM TYPE: Circular, medium-wide angle. Slight rings only.
    SWITCH TYPE: Pushbutton microswitches with digital signal processing.
    BEZEL: None
    BATTERY: 2 CR2016 lithium coin cells
    CURRENT CONSUMPTION: Varies, 2 uA to ~60 mA (req. re-measure)
    SUBMERSIBLE: No, but should be OK after accidental dunking
    ACCESSORIES: Batteries, split ring
    WARRANTY: Full lifetime


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