Light Output Vs Runtime Tests- Mtbr.com
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  1. #1
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    Light Output Vs Runtime Tests

    I was looking at some of the light output vs run time charts at We Test Lights | Independent Tests, Reviews and Technical Comparison of LED Lights and I found some rather disturbing charts.

    The caveats regarding these tests are that it is a light manufacturer doing the tests so there is some conflict of interest. There is no indication the airflow, if any, during the test. Nor is there any indication of the ambient test temperature. There is also no indication of what the battery voltage was at the end of the test.

    Light & Motion Taz 2000
    Light Output Vs Runtime Tests-light-motion-taz-2000.jpg
    This is what I'd expect from a well designed light. A little exponential reduction in light output as the light and driver warm up and then a near constant output until the battery's low voltage protection circuit trips, or by design, the light output drops to a lower level to serve as an emergency reserve to limp home with. What does concern me are the dips in light output near the end of the run. That suggests a problem of some kind.


    Magicshine MJ-880
    Light Output Vs Runtime Tests-magicshine-mj-880.jpg
    This suggests a serious oscillation problem with the driver, be it by design or defect. Those dips in output are over 500 lumen.


    Serfas E-Lume 1600
    Light Output Vs Runtime Tests-serfas-e-lume-1600.jpg
    This is another very seriously screwed up light driver. Those dips in light output are over 50%, 750 lumens. Seem overpriced at $99.


    Lupine Piko 4
    Light Output Vs Runtime Tests-lupine-piko-4.jpg
    More serious instability. I'd expect much better from a $335 light.


    Sigma Buster 2000 HL
    Light Output Vs Runtime Tests-sigma-buster-2000-hl.jpg
    What would otherwise look like a well designed light has got a few problems. A $270 light shouldn't have any functional problems.


    Magicshine Eagle M2
    Light Output Vs Runtime Tests-magicshine-eagle-m2.jpg
    The light reducing output by 1,000 lumens in 5 minutes is showing some serious design issues. The output is constantly fluctuating. It could be an unstable design, but it could also be showing signs of intermittent connections, often due to poor solder joints. Not what I could consider a 2,400 lumen light.


    Magicshine MJ-906
    Light Output Vs Runtime Tests-magicshine-mj-906.jpg
    Overall this light doesn't look too bad, but the light fluctuations are seriously worrisome. Will this light get you there in back? I wouldn't trust it.


    NiteRider Pro 1800 Race
    Light Output Vs Runtime Tests-niterider-pro-1800-race.jpg
    I don't know about you, but I'd hate to spend over $250 for a light that reduces it's output this much in just 5 minutes. The various spikes in output are also worrisome.


    Portland Design Works Lars Rover 810
    Light Output Vs Runtime Tests-portland-design-works-lars-rover-810.jpg
    I believe that this light uses a single Li-Ion cell, which accounts for the constantly decreasing light output. But it doesn't account for the erratic light output. That could be a design issue or defective circuit.


    Planet Bike Blaze 500 XLR
    Light Output Vs Runtime Tests-planet-bike-blaze-500-xlr.jpg
    Light output fluctuations that suggest problems with the light.


    LED drivers just aren't that complex. The semiconductor manufacturers usually give enough information in their application notes that an even an experienced electronic hobbyist can design a decent driver without these problems.

    Scott Novak

  2. #2
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    Quote Originally Posted by Scott Novak View Post
    I was looking at some of the light output vs run time charts at We Test Lights | Independent Tests, Reviews and Technical Comparison of LED Lights and I found some rather disturbing charts.

    The caveats regarding these tests are that it is a light manufacturer doing the tests so there is some conflict of interest. There is no indication the airflow, if any, during the test. Nor is there any indication of the ambient test temperature. There is also no indication of what the battery voltage was at the end of the test.






    Serfas E-Lume 1600
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    This is another very seriously screwed up light driver. Those dips in light output are over 50%, 750 lumens. Seem overpriced at $99.


    Lupine Piko 4
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    More serious instability. I'd expect much better from a $335 light.


    Scott Novak
    For these two lights I would guess thermal issues are the problem. With the E-lume the approx. 50% drop is typical of a thermal protection step-down. When it cools enough it goes back up in power only to overheat again and keeps repeating the cycle till it reaches a thermally stable output.

    The Lupine has linear thermal protection that reduces power gradually till it reaches a thermally stable output (because of the stable condition in it's case). If the conditions changes (more air flow, change in ambient temp.) it would adjust output to a new thermally stable level.
    Mole

  3. #3
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    In either case their designs are seriously screwed up.

    In the case of the Lupine Piko, my guess is that the temperature sensor is either way too far from the LEDs, or the sensor has too much thermal mass, or there is very poor thermal conductivity between the sensor and the LEDs. That would account for the serious overshoot. In any case, you should expect better for a light that expansive.

    Re: Serfas E-Lume 1600

    The chart speaks for itself. It's just a very bad design.

    Scott Novak

  4. #4
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    Quote Originally Posted by Scott Novak View Post
    In either case their designs are seriously screwed up.

    In the case of the Lupine Piko, my guess is that the temperature sensor is either way too far from the LEDs, or the sensor has too much thermal mass, or there is very poor thermal conductivity between the sensor and the LEDs. That would account for the serious overshoot. In any case, you should expect better for a light that expansive.

    Re: Serfas E-Lume 1600

    The chart speaks for itself. It's just a very bad design.

    Scott Novak
    Sounds like Lupine could improve the thermal protection system a little but for me the main problem is a 1500 lumen light will rarely be thermally stable at max. output with a 52 gram lighthead. Heatsink mass is just too small.

    E-lume is just the opposite. Large heatsink mass and surface area but either creates too much internal heat or very poor thermal path or both.

    Agree that both have serious design problems that should be corrected.
    Mole

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    Idea! Outbound Lighting Focal Series


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    I hope that Outbound's Lighting Focal Series actually perform this well under test. They are the most promising lights that I've seen.

    Scott Novak

  7. #7
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    Quote Originally Posted by angerdan View Post
    Keep in mind that this drop is specifically for the Adaptive mode. Where it is a designed drop over 45 minutes as your eyes adapt as a way to get more battery life without exaggerating claims.

    The 1500 lumen claim is based on the light in a steady state operating zone, around 85*C as per the datasheets. Or in other words, as it's sitting around in very low air conditions. As a lot of people on here know, as things heat up, output goes down. A lot of these company claims are based on the "best case" scenario, which I don't believe the we-test-lights guys do. Ideally would have a fan acting as cooling to provide the ideal test conditions. Even at a walking pace, the airflow makes a big different verses at a dead stop.

    This is the datasheet for the Altilon. Notice how at best case conditions it's actually almost 8% better than "operating". So that means when tested, or in motion on a bike, the OL lights may actually be 1600+ actual lumens.
    Light Output Vs Runtime Tests-lightcurve.jpg

    This is how almost all lights are rated as you guys can see. They take the initial operating condition and run with it. Even if it only lasts for a minute. However! In actual operation the airflow makes a massive thermal difference. So I'd be really curious if the testing is done with or without airflow.

    If the OL light was left on high, on a bench for 2 hours, it will step down a bit as there is a thermistor that monitors the junction temperature. Although it's monitoring to prevent overheating as in, sitting on a bench with no airflow in a 100* room kind of overheating. The case is designed to disparate a lot of heat quickly, but the primary minimum design condition is in motion at a minimum speed of 2mph (slow walking pace) in 90*F temperatures. Meaning that if being measured in a condition outside of that it'll be brighter and more stable (such as on a bike) or lower with some temperature correction occurring (such as on a bench for hours).

  8. #8
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    Light Output Vs Runtime Tests-bright-eyes-1200-lumen.jpg

    In this case the LED is a Lattice bright, which has high higher thermal resistance to case than the equivalent Cree LEDs. The PWB is glued to the baseplate with generic RTV with high thermal resistance. The baseplate only has contact with a narrow shoulder on the case with no thermally conductive compound applied at the interface.

    But thermal resistance alone doesn't account for a 40% reduction in output within 5 minutes. The driver has to play a significant role as well.

    I didn't notice any thermal protection circuits on the driver PWB or any thermal sensors on the LED PWB. But I haven't made a schematic diagram yet.

    There are other lights showing a drastic reduction in light output within a few minutes.

    Scott Novak

  9. #9
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    Quote Originally Posted by Scott Novak View Post
    .....I didn't notice any thermal protection circuits on the driver PWB or any thermal sensors on the LED PWB. But I haven't made a schematic diagram yet.
    Many of the common MCUs used for LED drivers have an internal thermister that is used for thermal stepdown input. Unfortunately, unless the MCU is closely thermal coupled to the housing the reaction is very delayed and function is impaired.
    GoPro adapters for bike lights http://www.pacifier.com/~kevinb/index.html

  10. #10
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    Vancbiker,

    With as much thermal resistance as the LED in the Bright Eyes light has, and considering that the only thermal path between the driver and the LED is internal convection and radiation, it's doubtful that the heat from the LED could affect the driver significantly within 5 minutes.

    Self heating of the driver circuit might explain it.

    Scott Novak

  11. #11
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    Quote Originally Posted by Scott Novak View Post
    ....With as much thermal resistance as the LED in the Bright Eyes light has, and considering that the only thermal path between the driver and the LED is internal convection and radiation, it's doubtful that the heat from the LED could affect the driver significantly within 5 minutes.

    Self heating of the driver circuit might explain it.
    That's pretty much what I've seen with most cheap lights.

    The drivers I use in my DIY lights have thermal vias to improve the thermal coupling and dissipate driver heat. I also install a beryllium copper "leaf spring" between the MCU and driver compartment lid to further improve the thermal coupling of the MCU to the housing
    GoPro adapters for bike lights http://www.pacifier.com/~kevinb/index.html

  12. #12
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    A riding buddy of mine made a comment about his Niterider Lumina OLED 800 that pointed out yet another drawback to single cell self-contained lights that loose a considerable amount of output in the first few minute's (not from thermal issues). After owning the light for a couple of yrs. he commented "It's just not as bright as it used to be". Comment I would expect to hear is it doesn't run as long as it used to but looking at the output vs. time charts I guess it's understandable even a slightly diminished runtime (from age weakened battery) will be enough to noticeably affect even initial brightness + shorten already limited runtime.
    Mole

  13. #13
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    So why not just use readily available, inexpensive 18650 batteries? You can carry a pocketful and then just keep on going way longer than the Energizer Bunny? It's the battery cell Tesla uses, as well as my Fenix bike light. No fear of going dark.

  14. #14
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    Quote Originally Posted by Nman View Post
    So why not just use readily available, inexpensive 18650 batteries? You can carry a pocketful and then just keep on going way longer than the Energizer Bunny? It's the battery cell Tesla uses, as well as my Fenix bike light. No fear of going dark.
    Field changeable batteries are a rarity for single cell self-contained lights. On top of that some of the lights tested showed a 50% drop in output within the first half hour so would be a PITA to keep output some what steady. Higher capacity batteries for anything over 500 lumens is what's needed for steady output and reasonable runtimes.
    Mole

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    Quote Originally Posted by Nman View Post
    So why not just use readily available, inexpensive 18650 batteries? You can carry a pocketful and then just keep on going way longer than the Energizer Bunny? It's the battery cell Tesla uses, as well as my Fenix bike light. No fear of going dark.
    IMHO self contained lights simply have too much mass and are prone to rotating out of position on the handlebars. Not to mention a having a limited run time in normal weather and an extremely limited run time in cold weather.

    For now I'm using this 6-18650 cell 2S3P battery box for my lights:

    https://forums.mtbr.com/lights-night...x-1084368.html

    It's got some problems, but for the moment it's the best available solution. In warm weather I can probably get by with only a pair of cells. But in cold weather I'll need to run all 6 cells, and preferably high current cells which have very low internal resistance.

    I'm running 18650 cells removed from dead battery packs that I get for free. Usually only one or two out of 8 cells are bad.

    Scott A. Novak

  16. #16
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    For small self contained lights - those 18650 generates a lot's of problems:
    - sealing the case for more than 2 cells.
    - size and contact issues 18-650 does not mean exactly 18mm and 65 mm it's 18-18,7 and 65-70mm there is a lot's of space needed if you want to be able to fit all the cells available on the market. Big are almost too big and small ones are rattling inside the case, sometimes loosing the contact.

  17. #17
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    FYI, wetestlights has added some new tests (big thanks for this!). Ones I noticed that were important IMO were Niterider Lumina 1200 & micro 850 and the Bontrager RT Pro (Ion 1300). I love that site!
    Mole

  18. #18
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    Other modes, battery capacity, and emitter efficiency


    Click on image to expand
    Light Output Vs Runtime Tests-lumina-1200-modes-cateye-v12.jpg

    High = White/Med. = Red

    I've seen interest expressed in how the lights perform in lower modes so I did High (1000 lumens) and Med. (550 Lumens) on the Lumina 1200 boost I recently picked up. I used the Cateye Volt 1200 as the host chart mainly because it has the longest time listed (that I saw) but it also serves as a good comparison between single cell/single emitter and dual cell/dual emitter of the same output. I didn't do low because its 275 lumen output is not a usable level for me except for emergencies and didn't want to spend that much time (6 hrs.) when it's pretty predictable that the output curve would end up almost flat. Performance of my Bontrager Ion was similar in the fact that each lower mode produced a longer running and flatter output curve and predict most self-contained lights over about 550 lumens (estimate the point at which most lights will operate at a stable level with the most commonly used battery capacity) will react the same. High beam comparison between the Volt and Lumina is a good example of how extra battery capacity + the added efficiency of using more emitters that are driven less hard equals a much longer and flatter output curve!
    Mole
    Last edited by MRMOLE; 12-21-2018 at 01:32 PM.

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