K2 Kroma Test:
Last Updated - 03/24/07 (Updates in Blue)
Runtime tests have been completed. Evaluation is pretty well complete except for minor details to be added in the future. Item #11 in "Overall Conclusions" below, has been substantially revised, so as to consider the possibilities of playing "Surefire Legos" with the K2/K2MS/U2 parts. This aspect will be periodically updated. Photos and beam shots have been added.
Photos: (courtesy of "Curse". Thanks "Curse"!)
Additional photos are available by "Curse" in Post #1.
From left to right: U2, K2 Kroma, K2 Kroma MilSpec.
A central LuxIII LED enveloped in a TIR optic, surrounded radially by 16 "3mm" LEDs, 8 Red, and 8 Blue.
Beam shots: (courtesy of "Curse". Thanks "Curse"!)
Additional beam shots are available by "Curse" in Post #1.
U2 & Kroma Series beam shots (distance - 16.5 feet, White mode)
Kroma beam shot (distance - 16.5 feet)
Introductory Remarks:
My runtime tests tend to be "to-the-death" or "lowest useful output", NOT the 50% point (unless otherwise noted). The High/Blue + High/White combo will have the brightest "perceived" output. The High/Red + High White combo will have the shortest runtime and produce the most heat, as a result of having the highest amperage draw. (Even though the literature says that the High Blue output is
4 lumens, and the High Red output is
5 lumens, the eye perceives the High Blue as
MUCH brighter than the High Red, being much more sensitive to the Blue/Green spectrum). The following order of brightness has been observed to be factual, no matter what the literature states.
Runtime Results: "High White" COMBO testing has been repeated to acquire a revised runtime recommendation. Please exercise extreme caution against high heat buildup!
High White+High Blue combo - brightest (54 Lumen output)..........
15 min. recommended, 20 min. max, due to high heat buildup. This is the position of brightest output, as perceived by the human eye, due to color sensitivity. 1006 mA draw observed by LEDMuseum on their DMM's 4A scale ("High White Only" is 819 mA). With the very slightly lower amperage draw than the "High White + High Red" combo, the runtimes might be expanded by a couple of minutes, and indeed, the temperature of the light felt a couple of degrees cooler, but I did not pursue things to a numerical conclusion.
Runtime test was ended at 20 minutes due to high heat buildup. At the 20-minute point, the whole body of the light was very warm, and the head was almost too hot to hold. Please keep in mind that heat continues to build up to the 60-90 minute point!!! 20 minutes was about the limit of my sense of humor for heat buildup. The F-70 filter was removed during this test to allow the heat to escape more easily. Ambient temperature was 70'F. You might get away with longer runtimes in the winter with colder temperatures for heat dissipation, but NOT during high ambient temperature conditions. The light was disassembled for cooling, as a courtesy to the LED head.
(The first, early runtime test ended in a panic due to
very high heat buildup. When I picked the light up after 41 minutes, I could not hold it in my hand. I ended the test for
fear of damage to the LED head. I won't do that again. Combos are for short runtimes only!! There seemed to be no reduction in output when I quit the test, but the heat buildup was fierce! I actually disassembled the light to cool things down faster (and it was difficult to touch the parts). It was so hot that this action seemed to be prudent. An F-70 filter was on the head at the time, helping to hold in the heat, and this was almost certainly part of the problem.
I never should have let it go this long! You guys do what you want, but I think that if you ran this light for the advertised 1 hour+ runtime in
ANY "High White" combination mode, you would be able to light your campfires with it by just throwing the thing into the middle of the damn woodpile.
It gets that hot!)
High White+High Red combo - 2nd brightest (55 lumen output)......
15 min. recommended, 20 min. max, due to high heat buildup. This is the position of highest heat buildup, highest amperage draw, fastest battery drain, and the broadest color spectrum. 1023 mA draw observed by LEDMuseum on their DMM's 4A scale ("High White Only" is 819 mA).
Runtime test was ended at 20 minutes due to high heat buildup. At the 20-minute point, the whole body of the light was very warm, and the head was almost too hot to hold. Please keep in mind that heat continues to build up to the 60-90 minute point!!! 20 minutes was about the limit of my sense of humor for heat buildup. The F-70 filter was removed during this test to allow the heat to escape more easily. Ambient temperature was 70'F. You might get away with longer runtimes in the winter with colder temperatures for heat dissipation, but NOT during high ambient temperature conditions. The light was disassembled for cooling, as a courtesy to the LED head.
High White+Low Blue combo - 3rd brightest (50.5 lumen output)....
20 min. recommended, 25 min. max, due to high heat buildup. Slightly lower amperage draws equal longer possible runtimes before high heat buildup, but not by much.
High White+Low Red combo - 4th brightest (50.5 lumen output).....
20 min. recommended, 25 min. max, due to high heat buildup. Slightly lower amperage draws equal longer possible runtimes before high heat buildup, but not by much.
IT IS NOW VERY OBVIOUS THAT THERE IS NOT ENOUGH METAL IN THE HEAD FOR LONG RUNTIMES IN ANY "HIGH WHITE" COMBINATION MODE , UNLESS AMBIENT TEMPERATURES ARE COLD. OTHERWISE, YOU HAVE TO KEEP RUNTIMES TO MODERATE LEVELS, OR RISK DAMAGE &/OR DETERIORATION TO THE LED HEAD.
I have copied the milliAmp-draw information from the LEDMuseum test on the K2, in the hopes that this will "shed some light" (sorry) on the heat problem of "High White Combos". They found that "High White Only" drew 819 mA on their DMM's 4A scale. Then they measured a 1023 mA draw for "High White+High Red", and a 1006 mA draw for "High White+High Blue". You may remember from above that the "High White+High Blue" output is the one that scared me so bad with the heat output, and this draw is less than that measured for "High White+High Red". I am not even remotely qualified to interpret this data and convert it into heat output danger, but someone may. If 819 mAs for "High White Only " translated into 132'F on "RadarGreg's" test, then 1023mA for "High White+High Red"............????!!!!
High White Only - 5th brightest (50 lumen output).........................
4+ hours (6 hours possible, especially with the assistance of adding "High Red", as needed, toward the end of the battery life). Continuous use probable, depending upon ambient conditions. Substantial heat buildup possible. Results have been duplicated several times. 819 mA draw observed by LEDMuseum on their DMM's 4A scale.
1st test.....4+ hours total, 1 1/2 hours full power, light reached 132'F @ 60-90 min., ambient temp during test was 74'F. Data from "RadarGreg". See full report below. Thanks "RadarGreg"! It was because of your work that I was motivated to duplicate your results for the benefit of all!
2nd test....4+ hours total, (6 hours possible, especially with the assistance of adding "High Red", as needed, toward the end of the battery life), ~1 1/2 hours full power, light reached ~ 130'F @ 50-100 min., ambient temp during test was 70'F. My results duplicated "RadarGreg's" results not just once, but twice. My results also showed that after 4 hours, my "high" position put out the same amount of light as the "low" position on fresh batteries - namely, .8-.9 lumens. Usable light (but very minimal) was still being produced at 6 hours. The maximum temperature reached on both "RadarGreg's" test, and mine, is just about the limit of my sense of humor concerning heat buildup (inexperience on my part?!). (The test was arbitrarily ended so that I could, once again, experiment, as I did at the end of test #3 under "Low White". Results of this 2nd experiment were identical to the 1st. When I asked for a "Blue" mode to be added to "High White" (it didn't matter which one, "low" or "high" because they were both the same intensity at this point), the spill angle and output increased, and the light was usable out to a slightly greater distance. Selecting "low red" also increased spill angle and output, but not as much as the Blue. Throughout each of these 3 selections, Low/High Blue or Low Red, there remained a central TIR hotspot for true-color assistance and "core" illumination. HOWEVER, when I selected "High Red", output GREATLY increased, the white TIR hotspot disappeared completely, and it was very obvious that this was the position of greatest output. (Keep in mind that we are splitting hairs about .1-.2 lumens). An additional fact noted was that the Red LEDs obviously draw more power than the Blue. You can tell this by the change in intensity of the White LED as you engage the Red modes over the top of "High White". (Whereas adding Low/High Blue does almost nothing to the White LED output level, "Low Red" does drop it somewhat and "High Red" eliminates it completely. The LEDMuseum mA draw measurements confirm this. This phenomenon was noted below, under the "Low White" test #3 results, but NOT the reason for it.)
3rd test....4+ hours total, (6 hours possible, especially with the assistance of adding "High Red", as needed, toward the end of the battery life), ~1 1/2 hours full power, light reached ~ 130'F @ 50-100 min., ambient temp during test was 70'F. The 3rd test results duplicated the 1st and 2nd test results exactly, complete to the experimentation at the end of the test. You could "copy" the results from test #2 and "paste" them here in test #3, word-for-word.
"LED61" successfully ran a BS 17650 in his Kroma and got 2 hours in "High White" with no reported problems as far as "powering" the light. However, see item #20 in "Overall Conclusions" below for another issue that emerged. Thanks "LED61"!
Thanks to the efforts of "RadarGreg", we have an idea of what "High White Only" will now do. He has the K2 Kroma, Milspec version, and my results for the regular K2 KROMA were identical with his. I quote his work:
"Ok, for all those that like to see numbers and measurements, I took a new set of Panasonic CR123A batteries and ran them in my Kroma MS on high white LED only. I wanted to see just how hot it got and how long it would run. The batteries tested 100% on my Ansmann Energy-Check LCD tester. The ambient temperature in my office here remained a steady 74 degrees Fahrenheit. My Kroma-MS was at ambient temperature of 74 degrees when I stated the test and I placed it on a small stand to isolate it as much as possible from any heat sink source. Below are the times and temperatures as I measured them on the head of the Kroma with an IR thermometer.
TIME TEMPERATURE(Fahrenheit)
09:58 74
10:00 84
10:05 104
10:10 115
10:15 118
10:20 121
10:30 123
10:35 125
10:45 128
11:00 130 Still as apparently bright as at the start
11:20 132
11:30 130
11:35 131
11:45 126 Appears a bit dimmer that at full charge
11:50 120
11:55 108
12:00 99
12:20 87
12:25 83
12:30 81
13:00 76
13:15 77
14:00 74 Light is still burning, but high power is now about at bright as low power on fully charged batteries.
Test was stopped at this point. The final battery readings on the Ansmann were 0% for both batteries and 1.09 VDC each. The Kroma was still able to produce useable light but nowhere nearly as much as the low power white level.
My overall expectation was to see just how hot the head would get and if it would be enough to cook the LEDs to a level where it might damage the circuitry. At a maximum temperature reading of only 132 degrees, I don't think that is hot enough to kill the electronics. However, in an environment where the ambient temperature is much higher (Iraq in the Summer, burning building, etc.) the Kroma would get hotter as there is less cooling air.
I don't think I'll be doing a runtime test on the other LED modes for the Red, Blue, IR and Yellow-Green. With the main white LED running for four hours and still producing useable light, I'd have to probably watch the blue LEDs burn for days, possibly a week. I hope you found this information useful. Thanks"
Technical note: On every test, just like clockwork, the temperature of the light began to fall just before the 1+40 hour point. This is a positive indication that the lumen output (and the resultant heat production) began to fall off just before that point, causing the temperature to fall. Thus, ~1 1/2 hours of full-power output is verified, and just seemed longer due to the eye's inability to perceive a small drop in lumen output. Coming off of "peak" output, a falling temperature is an immediate and FAR more accurate gauge of output reduction than the human eye.
Apparently, on my first, early test, I came within 14'F of "RadarGreg's" max. temperature, at my 17 minute point, and then "chickened-out". Thanks to "RadarGreg's" persistence, we have the above "High White Only" results, and I have been able to verify them twice. However, during my very first test of the "High White/High Blue" combo, the temperature appeared to be MUCH higher. Approach "High White" combos with extreme caution, please!!! Thus, my time-limited recommendations. Thanks "RadarGreg".
High Blue - 6th brightest due to eye sensitivity (4 lumens output).....
20 hours. Continuous use ok. No heat buildup observed.
Test terminated at 20 hours. Remaining output semi-worthless. As High Blue dimmed, Low Blue was also dimming underneath it. By the time I had reached 19 1/2 hours of runtime, High and Low Blue were identical in output - an "almost useless, moon-mode" output level. I could read my watch with it, but not much more. Interestingly enough, Low White was more useful at this point as a result of it's also limited (but focused) output. Even more interesting, Low Red was still usably bright, and High Red far brighter.
High Red - 7th brightest (5 lumens output)...................................
21 hours. Continuous use ok. No heat buildup observed.
At 20 1/2 hours runtime, High Red was still performing, albeit dimly. It was still visibly brighter than Low Red, but aside from reading in close, reading your watch, finding a keyhole, or puttering around within 6-12" inside of a pack, the overall light output was useless. Let's call it "moon-mode" only. Low Red could still be used at this point, to read print or read your watch, but only if you held the light in contact with the object. The light output was
that dim in Low Red. Just as we suspected, no other positions would function. Oh, with fully, night-adapted eyes, you could tell that there was current going to the White and Blue LEDs, but there was no usable output at all. At 21 hours, only High Red worked and the test was ended.
However, when I turned the light off, to rest the batteries for a few seconds, then turned the light back on, Low Red began to work again, everything got a little brighter, and we were back to the "20 1/2 hour characteristics" mentioned above.
Battery rest will rejuvenate the light for extended runtime.
I forgot to mention something when I was testing High Blue. As the light output began to diminish, two out of eight of the LEDs were noticeably dimmer than the rest (bad LEDs?, bad wiring?). Well, the same thing occurred when testing High Red, and these were different LEDs?! It didn't seem to affect the output, or beam symmetry at any output level. It was more of a curiosity.
Another curiosity observed was the sensitivity of the head position to lumen output. When I "giggled" the head a little, around the correct "detent" position for High Red, the output got noticeably brighter! The same was true for the Low Red position. Apparently, the contacts in the head are very sensitive to "exact position" for "maximum" output.
This sensitivity is not apparent when the batteries are fresh, but it certainly is when battery strength becomes very low. See item #5 in "Runtime Test Conclusions" below. For reasons unexplained, this phenomenon did not seem to come into play during the testing of "Low Blue" or "Low Red". I can't explain it. Perhaps breaking in a new light or whatever!?
Just as we suspected, when battery strength is lowest, the last position that will give you enough output to "see" is "High Red". Therefore,
"when the batteries are about dead, go High Red"! This was again confirmed after the "Low White" test.
Low Blue - 8th brightest due to eye sensitivity (.5 lumen output).....
46 hours. Continuous use ok. No heat buildup observed.
1st test........>45, <48 hours - a failure. Bad batteries? Continuous contact with metal? Insulated for 2nd test.
2nd test.......>46, <58 hours.
3rd test.........46.5 hours.
Very disappointing! Surefire projected 80 hours!
This was the position that I was counting on to come through for us. The only way to explain the poor performance in runtime is an efficiency loss in the head. If we are not going to be rewarded with long runtimes, there is no reason to choose one color over the other, unless a special function is required. It looks like we are going to end up with a tri-colored U2. No matter what "Low" position we choose, we will get about 45-50 hours of runtime. Choose the color for the function. I am currently doing runtimes on "Low Red", but that position is not powerful enough to be very useful beyond 5-8 feet, and thus does not affect the end result, philosophically speaking. Only "Low White" & "Low Blue" can be used for any distance application.
Low White - 9th brightest (.8-.9 lumen output - observed)..............
50 hours. Continuous use ok. No heat buildup observed.
1st test........>43, <55 hours.
2nd test.......>30, <37 hours. Very disappointing. (Results discounted due to probable weak batteries.)
3rd test........>53 hours.
4th test........>50, <57 hours.
Surefire advertises 20 hours. It looks like we can expect 50(+?) with good batteries, 30-35 with weaker ones.
During the
1st test, the last time that I observed the light was 43 hours after the test began. At that time the output looked normal (evidence of GOOD regulation). When I returned home 12 hours later, at the 55 hour mark, the light was dead. Thus the above result. >43 hours, <55 hours. Since this test is important, as are
all of the
"LOW" runtime tests, I immediately started the second test.
During the 2nd test, no one was more surprised than I when I awakened at the 37 hour point and the light was dead. It was alright when I went to bed 7 hours earlier. I know that Surefire only rates this position for 20 hours, but.....I can only assume, based on the results of the other three tests that test #2 was the result of weak batteries.
(A interesting side bar to the results of test #3: At the 53 hour point, when lumen output was approaching moon-mode status, I decided to arbitrarily end the test and experiment with the results of various combinations. When I selected "High White", the light output increased by a factor of 2 or 3. When I asked for a "Blue" mode to be added to this (it didn't matter which one, "low" or "high" because they were both the same intensity at this point), the field of view (spill angle) tripled, output increased, and the light was usable out to about 30' with fully night-adapted eyes. Selecting "low red" also increased spill and output, but not as much as the Blue. Throughout each of these 3 selections, Low/High Blue or Low Red, there remained a central TIR hotspot for true-color assistance and "core" illumination. HOWEVER, when I selected "High Red", output GREATLY increased, the white TIR hotspot disappeared completely, and it was very obvious that this was the position of greatest output. Once again, our axiom was validated - "When the batteries are about dead, select "High Red"!)
A thought: I had expected the runtime to be about 100 hours +/- because the lumen output has been observed to be half that of the U2.
Since my first three runtimes were similarly disappointing, I must suspect inefficiencies of the regulation circuit in the head. With the complexity of the head design, this would not surprise me, but I had hoped for better.
See Item #20 in "Overall Conclusions" below.
Low Red - 10th brightest (.5 lumen output)...................................
46 hours. Continuous use ok. No heat buildup observed.
1st test........>46, <47 hours. About the same runtime as "Low White" & "Low Blue".
2nd test.........47 hours.
Very disappointing! Surefire projected 80 hours!
Runtime Test Conclusions:
1. "High White" combinations are the problem as far as heat-buildup goes. Stay away from those settings and you probably have a continuous-duty light.
2. To avoid LED deterioration &/or destruction,
limit your runtime when using "High White" combination modes in any capacity. I conservatively recommend
15 minutes normal runtime, 20 minutes maximum,
a little longer for "low red" or "low blue" combos. Times can vary quite a bit due to outside air temperature and wind. Experiment with caution. This thing is too damn expensive to be careless. My runtime recommendations for the "High White Combos" above are based upon taking you to about the same temperatures reached in the "High White Only" mode (130-135'F), where the head was just about too hot to touch. This is the limit of my sense of humor for heat-abuse in a $300 light. From here on, it's up to you. Others, with more LED experience, will have to fine-tune these figures upward.
3. I doubt that we will acquire a
runtime for any
"High White" combination mode due to the detrimental and dangerous heat buildup. Not with
MY light anyway. If Surefire wants to claim 1 hr. +, that's ok with me. If you guys want to test this with
YOUR light, that's also fine with me. My life depends upon how long the other modes work, not the "High White"
combination modes. When I originally made the above statement, I included "High White Only" as well, and then, sure enough, "RadarGreg" DID test "High White Only" with HIS light, with the following results: 1 1/2 hrs. of full, regulated power. Max temp of 130-132'F, reached between 60 & 90 minutes. 4 hrs. of total light. Excellent. See details of his work above under "High White Only". (Thanks "RadarGreg". Apparently, I got within 14' of your results on the "High White Only" test and "chickened-out". His results have since been confirmed and expanded upon.
4. Battery rest will rejuvenate the light for extended runtime. I had a chance to play with this a little after the "Low Blue" testing, and learned the following: The longer you let the batteries rest, the longer they will work when the light is reactivated (within limits). In addition, it was again demonstrated that the position that will give you the most light upon reactivation is "High Red".
5. One curiosity observed was the
sensitivity of the head position to lumen output. When I "giggled" the head a little, around the correct "detent" position when testing High Red, the output got noticeably brighter! The same was true for the Low Red position. This also appears to be true for the High/Low Blue positions. Apparently, the contacts in the head are very sensitive to "exact position" for "maximum" output.
This sensitivity is not apparent when the batteries are fresh, but it certainly is when battery strength becomes very low. For reasons unexplained, this phenomenon did not seem to come into play during the testing of "Low Blue" or "Low Red". I can't explain it. Perhaps breaking in a new light or whatever!?
6. Just as we suspected, when battery strength is lowest, the last position that will give you enough output to "see" is "High Red". Therefore,
"when the batteries are about dead, go High Red"! This was again confirmed after the "Low White" test.
7. All runtimes tests have been as good or better than advertised by Surefire, except "Low Blue" and "Low Red". See item #26 below.
8. "Low White" will run the longest of the "Low" positions, but not by much. "High Red + High White" will run the shortest time.
Overall Evaluation / Conclusions:
1. How does it work? There are 21 lighting modes for this light:
Position 1: Locked out. Then, rotate the tail cap 360' clockwise to **** the light for the
next five functions and start: (with the head rotated full counterclockwise, push for Position 2: High Blue. Rotate the head one position clockwise and push for Position 3: Low Blue. Rotate the head one position clockwise to the middle position and push for Position 4: Low White. Rotate the head one more position clockwise to the right of center and push for Position 5: Low Red. Rotate the head one position clockwise to the full clockwise position and push for Position 6: High Red. Then, rotate the tail cap 360' clockwise again to **** the light for the
next five functions and start again: (with the head rotated full counterclockwise, push "easy" for Position 7: High Blue. Push harder to
add High White. Rotate the head one position clockwise and push "easy" for Position 8: Low Blue. Push harder to
add High White. Rotate the head one position clockwise to the middle position and push "easy" for Position 9: Low White. Push harder for High White. Rotate the head one more position clockwise to the right of center and push "easy" for Position 10: Low Red. Push harder to
add High White. Rotate the head one position clockwise to the full clockwise position and push "easy" for Position 11: High Red. Push harder to
add High White. Then, rotate the tail cap slightly clockwise again to engage the
next five functions of "constant on" and start again: (with the
head rotated full counterclockwise, you are engaged in
"constant on" Position 12: High Blue. Push to
add High White. Rotate the head one position clockwise and you are engaged in "constant on" Position 13: Low Blue. Push to
add High White. Rotate the head one position clockwise to the middle position and you are engaged in "constant on" Position 14: Low White. Push for High White. Rotate the head one more position clockwise to the right of center and you are engaged in "constant on" Position 15: Low Red. Push to
add High White. Rotate the head one position clockwise to the full clockwise position and you are engaged in "constant on" Position 16: High Red. Push to
add High White. Rotate the tail cap quite a bit more to the "constant on - High White" position and you begin the last five functions. With the head at full counterclockwise, you will be at Position 17: High Blue + High White "constant on" (Brightest Position available - shortest runtime - hottest). Rotate the head one position clockwise and you will be at Position 18: Low Blue + High White "constant on". Rotate the head one more position clockwise to the center position and you will be at Position 19: High White only "constant on". Rotate the head one position clockwise and you will be at Position 20: Low Red + High White "constant on". Rotate the head one position clockwise to the full clockwise position and you will be at Position 21: High Red + High White "constant on".
2. High Blue + High White is the brightest output combination when you need maximum
perceived brightness.
High Red + High White will give you the broadest color spectrum, produce the most heat, draw the most power, and drain the batteries the fastest.
3. Low white is an excellent close-up, true-color, work light for night-adapted eyes. It needs an F-70 or FM-64 to soften it for a flood effect. Otherwise, you will have an irritatingly small square of light to work with due to the TIR optic. Low White with an F-70 or FM-64 is comparable to but slightly dimmer than the L1/F04 combo on "low". Perfect for getting you to the bathroom without burning the back of your retinas out. Despite what the literature states ("Low White - 3 lumens / 20 hrs. runtime"),
Low White is closer to about .8-.9 lumens / 50 hours runtime. It's output is less than the L1 on "low" (1.1 lumens) and half of what the U2 is on "low" (2 lumens). This is actually a good thing for both runtime, and night-adapted utility purposes.
4. Low Blue is suitable for cross-country navigation.
High Red is better from a night-vision adaptation standpoint. I understand that Red light is invisible to deer and possibly other game so High Red would have to be used in walking to a hunting stand. Low Blue will run
twice as long as High Red. Please consider this when battery life is critical. Low Blue is also suitable for short-range blood-trail tracking. It's bright enough.
High Blue will reach out a lot farther. It is much brighter.
High Red is better for x-country travel than the "Low" position on the L1-RD. That always was a little too dim with too little spill for the job. The
High Red position of the K2,
without the F-70 filter, is
perfect.
5. High Blue is also a very nice short-range floodlight or camp-light flood.
6. Low Red is very good for very short-range work with fully night-adapted eyes.
12-36" work in "Tactical Red" (Illumination at distances beyond 5-8 feet is very marginal). Far too dim to be used for safe or rapid movement of any kind. You will have to use Low Blue or High Red for this.
7. High white has a very nice beam without the filter, a very nice short-range flood with the filter. Equivalent to the U2 on "level 4-5" if "level 1" is the dimmest. Adequate for most needs. Has the typical focused distance aspect of the TIR optic but with some spill for a more acceptable beam shape. Although the U2 has a better-shaped beam and puts out a little more light, the K2 out-throws it by a hair.
8. Versatility is the name of the game for this light.
I theorized that it would be the ideal "hunter's" flashlight, so I sent it off to Henderson, Tennessee with a friend for just such an evaluation. He has now returned and here are his impressions. He liked the light, overall. He is not used to using "red" light for "night-navigation" so he was not all that impressed with the feature. Another man with which he was hunting (a world champion archer) liked the "red" feature a lot. I also do a lot of night-navigation in rough country and I like the "red" feature as well. I think that the power level of "High Red" is "perfect" for this task. The Blue levels were appreciated for shorter-range campsite duties. He did not have a chance to do any blood trail tracking at night. He did his tracking during daylight hours. However, he did confirm that the Blue levels did show up blood as "black spots". (I understand that if you use "white" light with a "blue" filter, blood spots will phosphor somewhat and will be redder in color - someone please confirm. If so, you have an interesting combo possible for forensics or hunting - blood shows black under the Blue LEDs or phosphor red under the white beam if you had a blue filter on the front - interesting). The White levels were described as "adequate" for all required tasks. He liked the F-70 beam shaper filter on the front for the flood characteristics during several activities. Another interesting comment made by him is his admitted prejudice for a smaller light (ala E1L, E2L) for the sake of weight, bulk, and convenience. As a result, his "guarded approval" of this light is all the more significant. More recently, he voiced a preference for a smaller light (ala E1e/KL-1, E2L, L-1), regardless of how this would result in a loss of features - (old school, where weight and convenience is paramount).
I recently queried another hunter/outdoorsman about his impression of the K2, and he was effusive in his praise. He said that it was the most "full-featured light" that he had ever seen. He did not like the F-70 on the front of it. He felt that it cut down on the output too much. (Indeed it does! That flexibility is precisely what I do like, as well as the additional protection to the head). Just our opinions.
This light might also be the "Holy Grail" for aviators, as well as hunters. It does everything better than the "A2". Indeed, it is like a "tri-color", Hi/Lo A2. Now, you have the versatility of 3 LED colors, not just one, and each color has a Hi/Lo option. Blue is useful in the detection of hydraulic fluid, and should make it show up "black" on the pre-flight "walk around". You have two levels of "Red" for night-vision preservation with "utility" power, as well as two levels of "White", "Low" for close-up work and "Hi" for distance. "Low White" is now dim enough for true-color, close-up work, while preserving night vision. It also runs for 50 hours on 2 batteries instead of 10 hours. With an F-70 "slim line" beam shaper on the front, you protect the lens, and now have 12 options of Hi/Lo, flood/spot instead of just the 2 options on the A2. What's not to like about this?!
It is only in the "tactical capacity" that I will reserve judgment (for now). There is no argument, thus far, that the K2 functions brilliantly as a multi-purpose, backup, "utility light" in the field. The only question is whether or not you have need of the "yellow/green" and "infrared" compatibility with night-vision equipment. The military felt that you did, and that is why we have two versions of the K2/K2MS. If you do not have need of this capability, my preliminary feeling is that you would be better served by the civilian K2, with it's more versatile "Hi/Lo Blue" and "Hi/Lo Red" options. (After all, with the primary gun light task being assigned to another, more suitable unit, such as an M3 or something else, and the "emergency backup" task being taken care of by something like an L1 /F05, the only purpose of this light is "primary, multi-purpose, utility". So, the question that begs answering is "How much utility vs. how many purposes?"). This aspect will be investigated at length when I post my review of the K2MS.
9. Do
NOT use the Z-60
lanyard on the K2. Yes, you can sand down (open up) the inside diameter of the split ring attachment piece with a piece of sandpaper wrapped around a pipe of a slightly smaller diameter, but when you attach the split ring to the K2, you
CANNOT use the Z-60
lanyard with it's
metal clip on the end. The split ring hole is now so close to the metal on the tail cap that, when it rotates, the metal clip at the end of the Z-60 lanyard will
scratch the metal on the tail cap very quickly. You will have to remove the metal clip and just use the Para cord, or something that will not scratch the metal on the tail cap. Other than that, the
Z-60 split ring attachment can be sanded down to work just fine.
10. The U2 body is interchangeable with the "sleeved" (?) K2 body, so if you have an early "wide-open" U2 body, this will allow you to use about any battery you desire if you swapped out the bodies. I could not tell for sure but it looks like the K2 body might have a removable sleeve (ala U2 body / gen. 2). Someone else will have to report on this. I am not knowledgeable enough to do this. If you more knowledgeable people decide that the K2 body is indeed sleeved, please provide a link as to how we might best remove it so as to acquire a more utilitarian battery shell.
Very Important! See #20 below!
11. Surefire "Legos". You cannot swap the heads or tail caps with the U2. They will not work right.
Section A: What can you do with the U2/K2/K2MS bezel or head?
Recently, "grnamin" mated the U2 head with an A21 (Surefire, weapon light module) and the tail cap, for a 1-battery, U2 "Shorty". This same configuration is possible on the K2 and K2MS!!!!! It looks like an R123 battery is required to power any of the heads properly. When a CR123 primary was tried on two different U2 "Shorties", neither would function. When a CR123 was tried on a K2 "Shorty", the five positions of the head would function, but "High White" would not. It was also obvious that "High Blue" and "High Red" were NOT up to full speed. This thread is on the CPF "LED" forum. So far, it looks like the following combinations are possible if you have sufficient voltage available for proper operation:
A. Tail cap + A21 + U2/K2/K2MS head. 1-battery "Shorty". 3.6-3.7 volts needed for proper operation.
B. Tail cap + MH-90 + U2/K2/K2MS head. The MH-90 gives you a 2-battery, "quick-release", gun light body.
C. Tail cap + A19/MC123/Detonator + A21 + U2/K2/K2MS head. 2-battery "slim line" body. Z-26 lanyard ring use possible. The "Tail cap + A19 + A21 + Head" combination worked better than anything else for me in both form and function.
D. Tail cap + A21 + A12 + U2/K2/K2MS head. 2-battery "slim line" body. Z-26 lanyard ring use may or may not be possible. This combination did not work for me unless I used the Z73 tailcap (the new G-2 "lockout" tail cap), or the Z48/49 "clickon" combat tail caps. The Z41, Z58/59 failed to function correctly. Although the combination allows a very nice, smooth, slimline body, you could achieve almost the same effect by using the above combination in "C", which would then function properly with all tail caps. You could also just take the pocket clip off of the K2/U2 body, and still retain proper, designed function. Either of these solutions is probably the smarter move.
WARNING!! Experimenting with the A21 + A12 combination will cause you to screw the tail caps on with quite a bit of force in an attempt to get them to function properly. This will cause substantial deformation to the negative ends of the batteries with results that are unknown to me. I threw my batteries out after seeing the damage!!
E. Tail cap + A12 ( by itself) + U2/K2/K2MS head. WILL NOT FUNCTION PROPERLY!!! The tail cap will not screw on far enough. The A12 is made to attach to the "front" of the light, extend the light for 1 battery length, and accept the threads on the head, then have an A21 screw on to the back of it. It will not handle the threads of the tail cap.
F. The A19, MC123, and "Detonator" parts, by themselves, WILL NOT FUNCTION PROPERLY!!! The head will not screw into the front of the part far enough to tighten properly. They are made to attach to the "back" of a light, extend the light for 1 battery length and accept the threads of the tail cap.
G. The A21 will do both jobs by itself. It will accept both the threads of the head on the front end, and the tail cap on the back. The only problem now is finding a battery with a voltage that will allow the light to function properly.
H. The primary problem is the inside diameter of the various parts, and the batteries they will now accept for use. It looks like you will need 3.6 to 3.7 volts minimum to make the lights work properly. Otherwise, the light seems to drop out of regulation.
I. Tail cap + U2/K2/K2MS body + A12 (with 2x17500s) + U2/K2/K2MS head. For extended runtime (per "Chronos". Thanks "Chronos".) I don't know about the voltages involved. (As a cautionary note, the A12 addition now allows a 3xCR123 battery body. The U2 does not like 9 volts (3xCR123s)!! After my experience on the U2, I am not going to try 9 volts on the K2!)
NOTE: The A12, A19, MC123, A21, and (probably) the "Detonator" parts are not bored out as widely as the U2 body (gen. 1), and will, as a result, probably limit which batteries can be used with these particular parts. Plan accordingly. Since I do not use rechargeable batteries, I know absolutely nothing about the required dimensions for their use. Others, more knowledgeable than I, will have to chime in here. I believe that Posts #68-77 in this thread were discussing battery dimensions in detail and this will help.
Photo of a U2 "Shorty": (courtesy of "Grnamin". Thanks "Grnamin"!)
Section B: What can you do with the U2/K2/K2MS body?
If you are married to the idea of a "bezel-down" pocket clip, or just like the "form" of this body, you can use the U2/K2/K2MS body with the "LU-60" adapter piece screwed into the front end, and then use it with any standard bezel (i.e. C2/M2/KL-5/KL-3/Z-32 etc.). The U2/K2/K2MS bodies are dimensionally identical, so an early U2 body, bored out, or with the sleeve removed on the gen. 2, will give you more battery flexibility. Possible combos include:
A. K2 tail cap + K2 body + "LU-60" adapter piece + KL5 or KL-3 gives you a 2-stage LED light. (However, since the K2, 2-stage, White LED is very effective and you also pick up "High/Low Blue" and "High/Low Red", I don't know why you would want to do this.)
B. U2 tail cap + U2 body + "LU-60" adapter piece + C2/M2/Z-32 etc. for an incandescent light with a "bezel-down" pocket clip. Adding the A12 on the front of the body, or an A19/MC123/"Detonator" on the back of the body gives a 3-battery possibility (or the use of 2x17500s for extended runtime).
NOTE: Since the U2/K2/K2MS bodies are functionally identical, the key is in the tail cap. If you want an incan light, you must use a single-stage tail cap. I have successfully used the Z41, Z73, Z58, Z59, Z48, & Z49 on the U2. I understand that the SW01 and SW02 will also work. The key here is SINGLE-STAGE! You cannot use dual-stage tail caps on incandescent bulbs. They don't like the low voltage put out by the first stage.
Section C: What can you do with the K2/K2MS 2-stage tail cap?
A. 2-stage K2/K2MS tail cap + L5 = a 2-stage L5. (Both the K2, and the U2, are better lights, and throw farther.)
B. 2-stage K2/K2MS tail cap + L6 = a 2-stage L6. WARNING! I do not know what 9v will do to the resistor in the 2-stage K2/K2MS tail cap over time, since it is designed for 6v. I know it works but I have no idea about any long-term damage!!! More knowledgeable people will have to chime in here.
C. 2-stage K2/K2MS tail cap + a 2,3, or 4-battery body + a "Milkyspit" M/X-series head = a 2-stage "Milkyspit" light. WARNING! I do not know what 9v-12v will do to the resistor in the 2-stage K2/K2MS tail cap over time, since it is designed for 6v. I THINK it works, as it has been proven to do in the L6, but I have no idea about any long-term damage!!! More knowledgeable people will have to chime in here. Ask Milkyspit first!!!
D. In the same philosophical vein, the "LU-60A" adapter piece from the Surefire "Scout light" kit, will adapt a KL-3 or KL-5 to a Surefire L-1 or L-2 (or A2?) for the same result giving you a "slim line" mini-body (with the L-2 [or A2?]) or a "Shorty" (with the L-1). From my own experience, the L-1/LU-60A/KL-3(gen. 2, v. 3) is the best of the bunch! Beautiful!!
There are many other things that we CAN do. Just because we CAN, does not mean that we SHOULD. I hope some of this helps.
12. The o-ring on my K2 seems to be oversize. This makes rotation somewhat more difficult, but waterproof characteristics should be better as a result,
and the tail cap will be more resistant to inadvertent movement. One drawback of this tighter o-ring is that it is much more difficult to use one-handed.
13. With regard to the F-70 or FM-64 beam shaper filter on the front of the light, there are pros and cons. The beam shaper will protect the head (a BIG point in it's favor on a $300 light). It is necessary to soften things up in "Low White" for close, night-adapted work. It is necessary for a nice short-range "High White" camp-flood. It gives you 12 levels of light instead of 6. It is better when off or flipped up for "Low/High Blue" work, or "High Red" night-navigation. It is also necessary for it to be up or off for distance "High White" work. For "Low Red" work up close, it is a personal preference toss-up.
14. There are five rather subtle click-stops on the head of the light as you rotate the head from the full-counterclockwise position to the full-clockwise position. Since it would be fairly easy to rotate the head inadvertently off of a desired position, I used a silver-metallic "Sharpie" marker to mark the middle "Low White" position, and thus have a confirmed reference point every time I activate the light. I did the same thing on my U2 for "low" position, and that head is much more resistant to movement. I also do this to the witness marks on every one of my tail caps. It is more important on the tail caps of the L1, L2, A2, U2, K2, and K2MS than the rest of the Surefire lights because you will be going through several rotations to access all of the functions on these particular lights. Just a thought. See item #1 above to reference the complexity of the selection process. It is not nearly as bad as it first seems once you have the light in your hands, but it does save time not to have to fumble with a desired starting point.
15. I like this light. I like almost everything about it and I'll tell you why. I like it for it's small, lightweight, multi-function design philosophy. Instead of another "boat anchor", to be lugged around by the troops, Surefire created a compact, utilitarian instrument, which is really quite elegant. I think that it approaches "Holy Grail" status as a
hunter's flashlight. It has everything a hunter needs. If I were a hunter, I would add an L1, with a set of F0x filters as a backup, and call it quits.
I think that it also approaches "Holy Grail" status as an aviator's flashlight. You now have a "tri-color, Hi/Lo A2" that runs for 50 hours on 2 batteries instead of 10 hours. In a
tactical capacity, since you are going to have a primary gun light, this light serves as an excellent
multi-function backup. I know the U2 is far superior for "white light" versatility, but do you really
need the versatility? This light has a more functional "low" position - exactly what everyone wanted from the U2. As a matter of fact, this light has a "hatful" of multi-use "low" positions. The "high" position is reasonable, with a decent beam. In between, you have Low/High Blue and High Red to fill the gaps between "low white" and "high white". Additionally, you have "Low Red" tactical. Like the U2, "High White" can be flooded-out with an F-70 or FM-64 for a decent camp flood. Of course, other lights do each of these things a little bit better, but this light does all of them fairly well. It remains to be seen if the K2MS will do anything that much better, or if it will just be different. I suspect the latter. I ordered both just to see.
This light has now replaced my U2 as my primary "utility light".
16. Battery rest will rejuvenate the light for extended runtime.
I had a chance to play with this a little after the "Low Blue" testing, and learned the following: The longer you let the batteries rest, the longer they will work when the light is reactivated (within limits). In addition, it was again demonstrated that the position that will give you the most light upon reactivation is "High Red".
17. One curiosity observed was the
sensitivity of the head position to lumen output. When I "giggled" the head a little, around the correct "detent" position when testing High Red, the output got noticeably brighter! The same was true for the Low Red position. This also appears to be true for the High/Low Blue positions. Apparently, the contacts in the head are very sensitive to "exact position" for "maximum" output.
This sensitivity is not apparent when the batteries are fresh, but it certainly is when battery strength becomes very low. For reasons unexplained, this phenomenon did not seem to come into play during the testing of "Low Blue" or "Low Red". I can't explain it. Perhaps breaking in a new light or whatever!?
18. When I was testing High Blue, as the light output began to diminish,
two out of eight of the LEDs were noticeably dimmer than the rest (bad LEDs?, bad wiring?). The same thing occurred when testing High Red, and these were different LEDs?! It didn't seem to affect the output, or beam symmetry at any output level. It was more of a curiosity.
19. Just as we suspected, when battery strength is lowest, the last position that will give you enough output to "see" is "High Red". Therefore,
"when the batteries are about dead, go High Red"! This was again confirmed after the "Low White" test.
20. Voltage Sensitivity. "RadarGreg" and others more knowledgeable than I, have begun to experiment with different batteries on the K2MS model. They have begun to pick up evidence that the "head" (and it's resulting conduct) is very particular to "supplied voltage". I too am beginning to pick up evidence that the regulation circuit of the K2/K2MS is very sensitive to what powers it. There are apparently, inefficiencies &/or limitations in the head that make it very particular. I do not have the expertise to understand just what these peculiarities are, just that they are present. My runtimes are not nearly as long as I expected from a light with this power output. I also accidentally discovered that the light will not go to "High-White" in any switch position if you have a bad, low-voltage battery in the mix. See item #11 above.
"LED61" has successfully run the K2 in "High White" for 2 hours on a BS 17650 with no reported problems as far as "powering" the light. However, he also reports:
"I discovered a potential pitfall in using the rechargeable 17650. While the battery powers the light just fine at least in my case, and going back to the fact that it goes into the flashlight very tight and in a specific way, I accidentally dropped the light the other day and BAM!! all of the sudden no light. Turns out that the reduced length of the battery and the impact displaced the battery in such a way that it broke positive contact. So no matter how far I screwed the tailcap in it would not turn on. It was necessary to unscrew the tailcap, and press from the negative end until positive contact was reestablished. You would not want to mess around in this fashion in whatever emergency you needed the light for and so for serious use better use CR123's, or until I can figure out what sort of spacer I can insert in the negative end to insure there are no lose ends."
Thanks "LED61"!
So, even though, you may be able to "power" the light with a wide variety of batteries, by switching out the K2 body with a early U2, or just by using a different type of battery, the head may not tolerate it. So far!, the head seems very honest about displaying it's displeasure with what you are feeding it, but be careful folks. I'm not qualified to comment further.
21. "RadarGreg" brings the first "combat-application" report to the review. I quote him as follows:
"For the ones wondering if the Kroma can perform well in a tactical environment with the lumen output, I can say it did perform well. I had the chance to so shooting with several of the German CPF members this weekend, and we practiced illuminating targets at 15 meters and shooting them. (metal knockdown plates, not Tangos, hehe). The Kroma-MS illuminated the plate very well and gave enough sidespill to see several meters to either side as well. This would be important if in a dark area there was a second "bad guy" trying to hide just outside the hotspot. "
Thanks "RadarGreg"!
22. Quality Control report: There is a small smudge at the very apex of the TIR optic, on the inside of the TIR optic, that does not seem to affect the beam characteristics in any way. There is a "scuff" on the black plastic ring that holds the pocket clip in place on the light. Interestingly enough, it is identical to the scuff on my U2 and in exactly the same place?! (Same part, same assembly line process). The "click-stops" on the LED head have a minute amount of play in them.
23. Multiple LEDs in the head eliminate the possibility of the light failing due to a single bulb or LED failure. Now, your possible points of failure are reduced to batteries (always a possibility), tail cap (total failure doubtful), and regulation circuitry.
24. Beam Quality. The TIR optic assembly, which envelops the central Luxeon III LED, was incorporated to achieve maximum throw with minimum power consumption ("focused output"), ala L-1 (gen. 2) and KL-3 (gen. 2). Additionally, just like the other TIR-optic lights, there is a distant and irritating, circular artifact on both "Low" and "High". As a result, this "concentrated" beam needs to be softened with an F-70 or FM-64 for close-up work on "Low", or for use as an area camp flood on "High". However, a side benefit of this design is a very modest "distance capability" on "Low" and the ability to slightly "out-throw" the U2 on "High". The TIR optic appears to be a gen. 2 design because the "hotspot" is softer on both "Low" and "High" than the L-1 (gen. 2) and KL-3 (gen. 2), and the beam quality on "High" is "acceptable" without the F-70/FM-64, and has modest spill. There is no evidence of "Fresnel Lens" tinkering with the optic, but it is softer nonetheless.
Because of the multiple, radial LEDs for both Blue and Red, beam artifacts are minimal, and indeed, I doubt that you will notice them or be bothered by them during practical use. The primary purpose of using the F-70/FM-64 with these colors would be to give you 4 levels of intensity instead of 2. It really does make a substantial difference, especially on "High".
25. Odds & Ends. The light has a 1.47" bezel diameter, so all F-7s & FM-6x filters fit (anything that fits on an M-2, KL-3, or KL-5 etc). Bezel is lightly scalloped to visually warn you that the light is still on. The pocket clip is the bezel-down design, ala U2. Indeed, the body (only) is identical to and interchangeable with the U2. The central "WHITE" LED is a LuxIII in an "enveloping and focusing" TIR optic structure. This is surrounded radially by 16 "3mm" LEDs, 8 for "RED" and 8 for "BLUE". Since the light does not use a reflector, it is shorter and smaller than the U2. This is the result of the more compact and truncated head design, characteristic of a TIR optic assembly. This light is a "little" large for an EDC but smaller and shorter than the U2, and indeed, only 1/4" longer than the C2, with a slightly larger head. Finish is HA-"Black", ala U2.
26. All runtimes tests have been as good or better than advertised by Surefire, except "Low Blue" and "Low Red". As a result, we are now faced with the prospect of a tri-color U2 with 45-50 hours of runtime in a selected "Low" position (the U2 does about the same). OK......... I have to think about that for a while. The first thought that comes to mind is .....Do you want a tri-color, two-position K2 (Hi/Lo) or a single-color, 6-position U2? Then there is the K2MS, a 5-color light with "Hi/Lo" White. Apparently, as a result of the complexity of the head design, there are substantial efficiency loses, and we will not realize the 100+ hour runtimes expected, based upon lumen output. Not with the regular K2 anyway. I guess, when you start wiring 17 LEDs together in a rotating selector head, things begin to get complicated and efficiency begins to plummet! It is probably a miracle of design excellence that it works as well as it does. So, if you are not going to get increased runtimes with the K2 (over the U2), we are back to the color priority. If you need Hi/Lo Blue and Red, get the K2, if you don't, get the U2. Simple! (Until the K2MS enters the scene and complicates the issue!!!!)
27. I have decided to take my own advice and NOT purchase the K2 KROMA MilSpec. Since the red/blue options and red/blue beam-quality are FAR superior on the K2 KROMA, and I do NOT need the IR or yellow/green night-vision aspects of the MilSpec version, the K2 KROMA is a much better light for me.
28. This concludes my K2 KROMA review. As of 03/24/07, I do not plan to add any more information to this thread unless something develops. I hope that this report has been useful to all.
Hope this helps,
Flashdark sends,
Flashdark spends.
