Below is a review of the Fenix TK76 flashlight and its use in the underground/cave environment as well as it’s use as a light for underground photography and above ground lighting.
The light has three Cree LEDs, two flood and one spot and all three can be controlled independently. With all three lights on, it produces about 2800 lumin. The flashlight runs on 4 18650 batteries, although it can function with just two installed. The tests below were performed with Panasonic NCR 18650b batteries and charged by a Pila charger.
Starting with the flashing light on full on and letting it run down to point where it turned itself off took over 14 hours. The flashlight would step itself down as the power in the batteries drained and/or got too hot. With the flashing on at 2800 lumins, it is very hot to the touch. There are two heatsinks built into the flashlight.
For those not experienced underground, it would be difficult to find a harsher environment to test a light than in a cave. Caves have mud, cold, water, dirt, dust, rocks and darkness. Lighting in a cave environment is life critical. If a hiker above ground finds themselves without light, they can wait till daylight, underground, loss of light becomes critical and may result in rescue. For this reason, the test performed on the light where extreme. The testers did not just want to see how well the light worked, they wanted to see if can take the abuse of caving.
Best caving/speleological practice dictates that each caver carry at least three sources of light. Generally two mounted to a helmet and another either in a pocket or in a pack. This light functions as very capable third source with its ability to flood both a wide, tall or long passage. While using it in a large river passage, was able to light both walls about 20’ apart while shining 300’-400‘ down the passage. It can light a 75’ ceiling to a caver’s full field of vision. This is due to the fact this has a very focused spot as well as the two flood lights. The photos below were taken with the TK76 as the primary light source. Its battery life is remarkable as demonstrated below.
During a 7 hour cave trip, the light was used for both photography and general use. It was also used to search light for lost items both above and underwater. Underwater, the swimmers reported that light functioned flawlessly and was able to light underwater a good field of vision as well as penetrate the dark water to a better than expected distance. The light was used to a depth of about 6’ for about 15 minutes during this part of the test.
The light was frequently dropped in water, on rocks and into mud. It was dragged through underwater gravel and sand for distances of 20’ or more on multiple occasions (sometimes while crawling). While crawling on rock, some of which were underwater, the light was held in the cavers hand like a handle, supporting the upper body weight of the caver. The light was also intentionally placed face down on rocks, sand, gravel and mud. Sometimes with a bit of force and a couple of times unintentionally dropped and landed face down. Other than some cosmetic damage to the finish and some scratches and dings around face, the light was unscathed. Surprisingly, the lenses did not receive even a scratch. The buttons were operated under water and in mud in sand. At no time did water or debris infiltrate the flashlight despite one of the testers stated purpose was to try to break the light.
After 7 hours of caving and testing the light at mostly full and ¾ power, the flashlight still had over ½ charge left in it.
For use in cave photography, the flashlight is quite useful due the fact it is actually three lights in one. The photographer can control how much flood and spot he/she wants. The more narrow flood is a warmer light. A combination of all three can light formations near and far quite effectively. The narrow flood had a useful spread of about 90 degrees, the wider about 160. The spot (center LED) is quite focused, but when set on a lower setting than the floods was useful in highlighting details as well as allowing photographs of formations and structures far away.
The flashlight was able to out throw both the Zebra 600w and Sten. This not necessarily a fair comparison though, since those two lights are designed to be small, light and bright. But this is for the sake of comparison. The TK76 was about equally floody as the Zebra h602w, but the TK76 did throw more light and was brighter. These were the only higher end cave lights available for comparison.
Despite how durable and practical the light is in the underground environment, it does one major draw back and two things to consider. Although it does replace 3 lights, it is a bit on the heavy and large size (comparable to a full Nalgene bottle of water in approximate size and weight). Something to consider for extended trips. It would be a great light to bring into large caves, caves were high level of lighting is desired or for photography. One word of caution about placing it in a cave pack. It will turn on. The buttons don’t have a lockout function and if the turbo button is held down for 5 seconds, the light will stay on full high till either batteries run down or it overheats. Fenix suggestion was to loosen the tail cap until the battery no longer makes contact. This suggestion is not appropriate in the cave environment, as this would allow dirt and debris into the light. The testers solution was to take the battery out and put it in the handle upside down. It will fit, the light will close securely and the reverse polarity protection will protect the light. Fenix reports they are working on a better solution for this. A simple case or ability to lock out the buttons (say hold one of them down for 5 seconds) is all it would take.
The focus of these tests was in the cave environment, but the testers did “play” with it above aground. Standing on one of the testers patio, he was able to light his entire backyard brighter than daylight (it’s heavily shaded). This is a small yard, about 25’ wide and 60’ long. Standing at the end of his 120’ driveway, it was possible to light up his entire garage and driveway. The tester is considering replacing the headlights on his truck with two TK76s if he could figure out a way to control the light from the drivers seat and wire them to the truck batteries. The flashlight was able to light up a house 1 city block away while lighting a street curb to curb for about 50’.
After being taken on night hike a couple of tips.
Use it on lowest power that is effective. It’s tempting to blast the trail and flood it with light, but it really isn’t necessary and the light becomes warm.
It’s a bug magnet when full on.
NEVER point it at your face, it hurts if you get blasted (the instructions warn you of this)
You actually can see bones and tendons in your hands when you shine the light through your hand.
For search and rescue light, it would be hard to imagine something with more utility. The testers, even though they had used the light for over 20 hours, were consistently surprised by how well it lit up the darkness and to its brightness.
This is not your grandpa’s mag light. This is a serious light with amazing capabilities. A great tool for underground exploration and photography despite it being a little heavy and large. The only improvement the testers would like to see is way to lock out the buttons. Other than that, the time and money Fenix spent engineering and building the TK76 has paid off.
Original text link: