Trek 400 EX40

Trek 400 EX40, retail $199 (
Manufactured by Tektite Industries (
Last updated 03-22-08

Q: What's black & blue and has 40 white, beady little eyes?

A: Nope, it's not a radioactive poison dart frog in a blender. It's just the new Trek 400 EX40, a 4-C cell diving light featuring 40 screaming bright white Nichia LEDs!

The surprisingly compact, 17-ounce diving light is just as at home on land as it is under water; so don't let the term "diving light" put you off. The EX40 features a dual switching mechanism with lock-off capability, and is submersible to 300 feet.


The EX40 comes in a plastic tube capped at both ends. Pull off one of the caps and dump out the flashlight.

Install the batteries (see below) and it's ready to use.

The EX40 has two switches: a lever type switch that moves side to side, and a backup switch that can be used to turn the light on by tightening the bezel. When holding the EX40 with the lever switch facing up towards you, the "OFF" position places the lever switch to the right; moving it to the left turns the light on, and moving it back to the right turns it off. More on the switches later in this article.

To load the EX40, unscrew & remove the clear bezel and black LED assembly. Load the batteries in following the (+) and (-) indicators embossed next to each compartment. Now, hold the light so the lever switch faces your chest, and flip it all the way to your left. Place the LED module in the barrel, aligning the large cutout on its base with the switch assembly inside the barrel, and start screwing the bezel on. When the light comes on, tighten it only a little more (a 20th of a turn, or around 1/2 an inch is plenty!), and test the lever switch. It should turn the light off and on; if it stays on, unscrew the bezel slightly and try again until it is functioning properly. This puts the light into the "normal" operating mode.

Battery life is stated at "up to 5 hours" of bright light, and many additional hours of dimming, but still useful light. I'll run some burn time tests on it and come back here with actual values.

Business end

Like its bigger brother, the EX40 is made from sturdy polycarbonate and G.E. Lexan plastic, and is quite tough as plastic flashlights go. In the xenon/incandescent version of the Trek 400, the weak spot tended to be the batteries themselves, as their nipples became flattened flush with the top of the battery when the unit was dropped face-first. The EX40 was originally designed to be an entry-level diving light, or a secondary/backup diving light for the real experts; and most people in that position tend to take care of their equipment. Accidents do happen though. Things can fall when being removed from a car trunk, boats can hit heavy seas and throw equipment to the deck, a caver might have it get knocked out of a backpack, or the neighbor kid might sneak it during a slumber party and drop it in the tub or toilet. Since the vast majority of accidents involving this particular light will tend to occur at waist-height or less (tables, lip of car trunk, stowage cubby on small boat, etc.), that's the height I'll drop test this sample from after I've run all the photometric studies and battery life tests on it.

Under the clear Lexan bezel, you'll see not a glass bulb, but an array of 40 prime Nichia white LEDs. Each LED is mounted to the round PCB on its own standoff; this helps keep them aligned in case the flashlight is dropped, banged, or is otherwise manhandled. A pair of very large silicon diodes is present underneath the LED board to drop the battery voltage slightly and prevent the type of overcurrent that would otherwise cause thermal runaway and subsequent damage to the LEDs if a particularly potent set of batteries ends up going in the flashlight.

In the battery compartment you'll see a black plastic seperator; this helps keep the topmost batteries aligned with the contacts on the lamp module's base for increased reliability. The flashlight will still work without this piece; but you should not try to remove it on purpose.

The EX40 is equipped with both a primary and a backup switching mechanism. The primary switch is the small black lever located just behind the clear bezel assembly; flip this to one side to turn it on, and flip it the other way to turn it off. Both the on and off positions are equipped with detents, so it isn't very likely that you'll make the light go out just by bumping it or knocking it into something. The off position even has a second detent as extra assurance that it doesn't come on by itself or through casual handling.

Should something untoward happen to this switch, the light has a backup mechanism that allows you to turn it on and off simply by rotating the bezel. The bezel is *very* stiff, so you cannot change its position by accident - you have to do this with both hands. This also gives the light a built-in "lock out" fuction; simply turn the light on using the regular switch, unscrew the bezel until it turns off, and then turn the regular switch off. This prevents unwanted activation during storage or transport.

Although it is inadvisable to use the bezel as a switch while underwater during normal operation, if your main switch breaks and your light goes out, then by all means turn it back on using this backup system - that's what it's there for.

The beam of the EX40 is exceptionally clear and smooth, with no rings, spots, or other little evil things in it. I would consider this to be a "medium flood", with a wider than usual beam for a light using mostly 20 Nichias. Part of this is due to the large emitting area; approximately 45mm instead of 5mm a single LED would have; and part of it is due to the way the LEDs are aimed; in concert this gives an apparent effective viewing angle of 22-24 and maybe more at closer distances. And although it is being sold as a diving light, it is equally at home on dry land. The LEDs are being conservatively driven (though a bit harder than those in the EX60), and the flashlight should never overheat. If you really must have more light, there is a hack available for the EX40 that can be done by you at no cost, but it will void your warranty and cause irreversible damage if the batteries are subsequently installed incorrectly - not a matter to be taken lightly on a $200 dive light!

The EX40 comes equipped with a heavy duty, adjustable lanyard affixed to a sturdy eyelet on the back of the light. The lanyard has a length of rubber tubing to cushion your wrist, and has a spring loaded slide lock to adjust the size of the lanyard's loop. When fully open, the lanyard fits all the way around the flashlight, allowing you to securely hang it from a tree branch, pole, pipe, or other fixture.

Beam photograph on the test target at 12".
Measures 345,000mcd on a Meterman LM631 light meter.

Spectrographic plot
Spectrographic analysis of the LEDs in this flashlight.
USB2000 spectrometer graciously donated by P.L.

ProMetric analysis
Beam cross-sectional analysis.
Image made using the ProMetric System by Radiant Imaging.

Test unit was received in late April 2001; things have been very busy around here but I'm finally getting around to testing & measuring this flashlight along with several others in the queue.

A careful examination of the flashlight did not turn up any platinum catalyst pellets; these are commonly used in sealed flashlights to absorb hydrogen from stressed batteries.

UPDATE: 03-15-08
I attempted to change the batteries in the unit to perform spectrographic & beam cross-sectional analyses, and it broke.
The internal portion of the switch mechanism became broken into three pieces, and the "backup" switching mechanism (twisting the bezel) did not do the trick either.
As a result of this unexpected and unwarranted breakage, I have derated this product a little on my website.

UPDATE: 03-15-08
No, you aren't seeing things.
Yes, a same-day update.
My contact at Tektite responded rather promptly, and will be sending me a replacement flashlight body (the switch mechanism has to be installed with a special compression jig, so I could not replace the switch myself); so those analyses I wanted to do will get done after all.

UPDATE: 03-22-08
The replacement body arrived on the afternoon of 03-21-08; I promptly installed batteries in it and performed the two analyses on it that I wanted to do earlier.
Because the body also included a bezel, I'll be able to replace the fouled bezel on my Trek 6000 EX60 with the original bezel from my broken EX40 body as soon as I locate the EX60; this will allow me to perform a spectrographic analysis of it too - as I see it needs to have done.

My original EX40's lifeless, broken body now rests in the garbage can - to be placed in the dipsty dumpster as soon as the bag is full.
Directly below is a photograph showing just that.
Hmmm...maybe I should salvage those O-rings...there, done!!!

Brighter than heck
Durable construction
Uses common, easily available batteries
Reasonable burn-time considering the brightness
Reverse polarity protection
Failsafe switching with both primary and backup switches
Submersible to 300 feet
Does not appear to overdrive its LEDs, will retain "like new" brightness longer.

When fully loaded, it is a heavy light above ground; but will "weigh" less when used underwater.
Possibility of damage to the batteries (crushing of battery's (+) nipples) if dropped face-first.

    MANUFACTURER: Tektite Industries
    PRODUCT TYPE: Dive light
    LAMP TYPE: LED, 5mm white
    No. OF LAMPS: 40
    BEAM TYPE: Medium flood w/ soft falloff
    SWITCH TYPE: Lever type on/off, twist-bezel backup
    BEZEL: Clear Lexan
    BATTERY: 4x C-cells
    WATER RESISTANT: Yes (it's a dive light!) ;-)
    SUBMERSIBLE: Yes, to 300 feet
    ACCESSORIES: Generous padded lanyard
    WARRANTY: Lifetime, including LEDs


    Star Rating


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