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  1. #351
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    Quote Originally Posted by Titus Maximus View Post
    Question, does a hot or very warm casing indicate poor or good thermal management? Francois has posited that a cool casing is an indication that heat from the LED's is being dissipated well. I seem to recall a contention voiced in these forums that a warm casing is indication of good thermal transfer. Which is it? Or is the answer not so black and white. Discuss.
    I would say not that simple. What you want is consistent temperature throughout the whole unit, as if it was solid. The important parameter is the temperature inside the light, where the LED and the electronics live.

    A simple touch test of the outside casing doesn't really tell you how well the internals are thermally connected to the housing. A well designed and manufactured light may feel cool to the touch when under normal operating conditions (air moving over it), but the same unit badly assembled so that it had very poor thermal conductivity to the housing would also feel cool (actually cooler) but meanwhile the internals are burning up because the excess heat is not being drawn away.

    The only real way to tell its thermal stability is to measure the inside temperature over a period of time, but this is not usually possible from a practical basis.

    One thing that can be done fairly easily is to measure the housing temperature of a test sample against a known, good reference of the exact same light.

    Under the same operating conditions, the test sample should have the same housing temp as the reference if it's working properly. If the test sample has a lower housing temp then it's an indicator that it has poorer thermal conductivity than the reference and will probably fail earlier.

    Unfortunately this only identifies poorly made units of the same design but does not provide any information regarding how good the design itself is.

  2. #352
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    Hi Francois

    I ask you again
    Why do you write Philips SafeRide is 400 Claimed Lumen?
    Manufacturer(PHILIPS) announces it as 270 Lumen in Germany.
    The USA version is announced as 400 Lumen?

    Vienna1

  3. #353
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    Why is mtbr.com so slow?
    I remember it was not all 2 or 3 years ago.
    Always I must reload many times before I can see a page.
    And even when I can see a page, almost pictures are not shown.
    Almost pictures are shown as broken icons.
    Can regular members here read and post comfortably?

  4. #354
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    Quote Originally Posted by Vienna1 View Post
    Why is mtbr.com so slow?
    I remember it was not all 2 or 3 years ago.
    Always I must reload many times before I can see a page.
    And even when I can see a page, almost pictures are not shown.
    Almost pictures are shown as broken icons.
    Can regular members here read and post comfortably?
    Where exactly are you accessing the site from? What kind of browser and computer? Is just the forums slow or the whole website?

    Can you check loads.in - test how fast a webpage loads in a real browser from over 50 locations worldwide website? Enter our URL and it will show you if there are any bottlenecks in the server.

    fc

  5. #355
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    Quote Originally Posted by Vienna1 View Post
    Hi Francois

    I ask you again
    Why do you write Philips SafeRide is 400 Claimed Lumen?
    Manufacturer(PHILIPS) announces it as 270 Lumen in Germany.
    The USA version is announced as 400 Lumen?

    Vienna1
    400 lumen is my estimate of it and is a placeholder. I'll confirm with them what the declared lumen output is.

    fc

  6. #356
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    Quote Originally Posted by Titus Maximus View Post
    Question, does a hot or very warm casing indicate poor or good thermal management? Francois has posited that a cool casing is an indication that heat from the LED's is being dissipated well. I seem to recall a contention voiced in these forums that a warm casing is indication of good thermal transfer. Which is it? Or is the answer not so black and white. Discuss.
    We have to assume that the LED is transferring heat to the case in a modern production light.

    In my experience handling at least a hundred lights now, a tiny light head with many leds will get very hot compared to the same leds with a huge light head. It's all about surface area to dissipate the heat.

    A key issue is electronics heat protection mode. Good lights will step down the light output as the temperature increases. So one has to avoid this stepping down if comparing heat dissipation.

    Another interesting factor is dual-casing. Good lights have many heatsink fins encased in an outer shell that directs airflow. The outer case won't get as hot as the fins.

    That being said, I have a temp gun but I'm not sure what is a worthy data collection regarding heat.

    fc

  7. #357
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    The Urban 500 review is out.

    Light & Motion Urban 500, Urban 300 and Urban 180 – 2012 Mtbr Lights Shootout | Mountain Bike Review

    Does anybody own this light yet?

    The only big downfall is this is not intended for mountain biking use and the 'yellow' side visibility lights cannot be turned off. They punched holes in the reflector to get that light out. I suppose there are workarounds.

    fc

  8. #358
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    Quote Originally Posted by francois View Post
    We have to assume that the LED is transferring heat to the case in a modern production light.
    not to be argumentative, but we can't assume that at all. Perhaps in the higher quality lights, but I've seen several Magicshines where the emitter doesn't have any thermal paste under it or the light board isn't thermally coupled to the housing. Even if the LED is thermally coupled that in turn doesn't mean that the thermal paths throughout the case are well coupled - there have been at least a couple of MJ-872 owners complaining of thermal issues, most likely due to its multipart case.

  9. #359
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    If I might expand a little on your already good insights into thermal management...

    "We have to assume that the LED is transferring heat to the case in a modern production light."

    Generally speaking, this is true. However, to do it really well and achieve a consistently optimal mechanical interface between two structures is not a process that is very conducive to mass production. Just take a look at the aftermarket PC-cooling technology. Often, significant improvements can be made with the judicious application of thermal epoxies and thermal compounds, sometimes expensive. Great care has to be taken during application to achieve the thinnest possible layer of material with no voids or air gaps, so it can be tedious and time consuming, which are two things that manufacturers really want to avoid to keep costs down. Making this kind of good thermal connection between the control electronics and the case can be even trickier.

    "In my experience handling at least a hundred lights now, a tiny light head with many leds will get very hot compared to the same leds with a huge light head. It's all about surface area to dissipate the heat."

    True, and I would expand on that a bit by saying it's a combination of mass and total cooling surface area. A physically large light could actually have much less usable cooling surface area than a smaller light with many cooling "fins." However, the larger mass takes longer to "soak through" or reach steady-state. With no air flow, the larger light can become just as hot as the smaller light (assuming similar surface area), given enough time. Once the body of the light has reached steady-state, then it becomes all about convective cooling and the effectiveness of the heat sink design.

    "A key issue is electronics heat protection mode. Good lights will step down the light output as the temperature increases. So one has to avoid this stepping down if comparing heat dissipation."

    Another very true statement. One of the interesting aspects of this idea is that most, if not all of the circuit designs out there rely on a temperature sensor that is physically on the control circuit board and not co-located directly at the LED. As such, for really effective LED temperature monitoring, you need the best possible thermal path between the LEDs and the temp sensor on the circuit board to prevent huge variations in the protection ability as a function of air flow. "Self-protection" has definitely come up on other forum topics, but with the high power LEDs, it's still a bit of a gray area as to how well this may actually be protecting the LEDs under various air-flow conditions. So yes, most lights will have this "feature," but not all lights do it equally well, and some don't do it very well at all by not protecting soon enough at safe temperatures.

    "Another interesting factor is dual-casing. Good lights have many heatsink fins encased in an outer shell that directs airflow. The outer case won't get as hot as the fins."

    I might have to take exception with this one...
    In my humble opinion, there is no good reason (from an engineering standpoint) to encase your primary heat-dissipating element. Maybe from a safety and aesthetics standpoint, yes, but from the standpoint of operational efficiency, no. The outer casing in this situation is really more of a heat "shield" and actually reflects some of the heat back into the light, causing it to get even hotter in low to no air-flow situations than it would normally. The degree to which the outer casing on this small of a scale can effectively "direct" the air flow any better than a well designed "finned" heat sink in a free flow of air is questionable to me. I guess if it works, maybe it'll prove to be an OK thing, I just wouldn't go so far as to say its a characteristic of "good" lights. Again, just my opinion.

    "That being said, I have a temp gun but I'm not sure what is a worthy data collection regarding heat."

    You're right. It's a tough parameter to quantify. In general, given that good heat management is all about preserving the maximum output of the LEDs over their lifetime, the most important measurement you can make is the temperature right at the LED. Given that this is virtually impossible without modifications to the light, the next best thing would be to observe that the housing does a good job of extracting heat with air flow. In my thinking, this would be represented by the difference between the maximum observed case temperature with no air flow (before protection kicks in) and the highest steady-state case temperature while running with good air flow. In general, you'd hope to see the no-air-flow max case temp before protection not exceed 120 to 130F. Not sure how you would quantify it on the "encased" lights. Of course you would then have to "weight" the results by the total watts dissipated, so all in all, its a nightmare.

    Thanks for all that you're doing to sort through the labyrinth of lights out there and make them more accessible to all of us.

  10. #360
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    Quote Originally Posted by francois View Post
    We have to assume that the LED is transferring heat to the case in a modern production light.
    I have to agree with the others that this is not really a valid assumption. Every light will have a thermal resistance value between the LED junction and the air around the case. It's the sum of all the individual resistances for the thermal boundaries between the LED die and the exterior of the case. For the lights that are well engineered, the engineering team will have a pretty good idea of this value. They will have calculated the value based on the design and taken actual measurement on prototype lights. There really isn't a good and bad, there's a quantitative value for each light and if they were all known I'm sure you'd find a nice even distribution from best to worst across all the different lights you're testing.

    I do agree from a practical perspective, you really don't have a good way to directly measure the total thermal resistance or collect the data from the light makers. But, there is a fairly easy way to get a pretty accurate approximation. And I was intrigued that you actually touched on this with your integrating sphere measurements. The total thermal resistance between the LED junction and the case will be directly proportional to the drop in brightness between the time the light is first turned on and after it's settled to a stable temperature. The main thing you'll need to keep constant is the airflow over the light. The temperature will need to be constant to a lesser extent, but +-5 degrees that would be typical inside a house isn't going to make that much difference if the airflow is consistent.

  11. #361
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    It's probably also worth noting that the time it takes for the temperature to stabilize will be proportional to the mass of the light. Little lights with low mass will stabilize more quickly than bigger lights with lots of mass. If you really care about measuring the quality of the thermal path, you'll look at the difference between initial and stabilized light output independent of how long it takes for the light output to stabilize.

    Since most biker really care how much light is produced over the bulk of their ride, I would contend that the steady state light output is really what's important, as opposed to the initial brightness.

    You may already be doing this with your lux measurements, since I don't know the exact procedure you use.

  12. #362
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    I agree that it isn't a safe to assume there is good conduction between the LED and heat sink.

    I'd say your best bet would be to place the IR thermometer on the lens directly in front of a centrally located LED after the light has been run inside, in a controlled environment for, say, 15 minutes. Most of the heat, of course, isn't emitted from the front side of the LED, and the lens will interfere some, but that is the closest you'll get to where the heat is being generated. The temperature will be much lower than the temp on the backside, but the hotter the front side is, the hotter the back side must be. It'll provide a basis of comparison for lights running similar LED's at similar power levels.

    It might be interesting to repeat the test in front of a table fan set on low.

  13. #363
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    I can aim the laser temp gun at the led itself. Will that get the temp of the lens or the LED? I can compare it to temp of top front of the casing.

    Thanks Pethelman and the gang for the knowledge.

    fc

  14. #364
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    I think it'll get a bit of both, but mostly whatever is hotter. I can feel the heat of the sun through a window, but if the window is cold you might feel that cold if you're right next to it. Some glass can also block IR. You could probably get an idea by taking a lens off one of the lights, holding it in front of a known heat source, and seeing what the difference is.

    It probably doesn't matter much though since they'll ALL be through the lens. If similar glass is used you'd expect similar results. I know my HID light puts a lot of heat out through the glass even though the glass itself doesn't get that hot, so the glass on that light must be transmitting most of the radiation.

    One challenge to getting consistent results though will be the size of the area sampeled. The emissivity of the reflector will be much, MUCH lower than the suface of the LED itself, so could lead to unusually cool measurments if some of the reflector is sampeled.

  15. #365
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    Hey Francis did you receive the lights form CygoLite yet?

  16. #366
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    Quote Originally Posted by djembe975 View Post
    Hey Francis did you receive the lights form CygoLite yet?
    UPS tracking says:
    Delivered On:
    Wednesday, 10/19/2011 at 11:57 A.M.
    Left At:
    Front Door

    It should be waiting for me after my epic night ride tonight.

    fc

  17. #367
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    You should do a glory trip with this set up on your bar, maybe a few more hanging below the bar, and a light attached to every vent in your helmet. You'd be blazin'.


  18. #368
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    Quote Originally Posted by Vienna1 View Post
    Hi Francois

    I ask you again
    Why do you write Philips SafeRide is 400 Claimed Lumen?
    Manufacturer(PHILIPS) announces it as 270 Lumen in Germany.
    The USA version is announced as 400 Lumen?

    Vienna1
    I talked to them and they do not know what their lumens output is. It's marketed as 80 Lux in Germany

    Until they measure it or make a claim for the US light, I'm going to put:

    400 Lumens (mtbr estimate)

    It's certainly brighter than 270 lumens and it measures the same as several 400-500 lumen lights in my lux meter.

    fc

  19. #369
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    Quote Originally Posted by francois View Post
    I talked to them and they do not know what their lumens output is. It's marketed as 80 Lux in Germany

    Until they measure it or make a claim for the US light, I'm going to put:

    400 Lumens (mtbr estimate)

    It's certainly brighter than 270 lumens and it measures the same as several 400-500 lumen lights in my lux meter.

    fc
    Perhaps Vienna1 is confusing it with the dynamo driven version which presumably puts out less light?
    "... displays the social skills of a barrel cactus." - TNC

  20. #370
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    I've read about somebody measuring this to be 291 lumens. Based on the current draw and the Luxeon Rebel LED specs, somebody else has estimated to be around 270 lumens. BTW, the philips webiste says "220 lumens on the beam", so that may be a honest figure taking into account optical losses? For a shaped beam like the Philips, lux (lumens per square meter) at a specified distance (e.g., 10m) makes more sense than lumens. It appears a *whole* lot brighter than the lumen spec suggests because it concentrating all the output on to the road. For example the Philips appears to illuminate the road better than the Sigma Power LED EVO 900 (claimed 900 lumens) and with superior throw as well!

    Quote Originally Posted by francois View Post
    I talked to them and they do not know what their lumens output is. It's marketed as 80 Lux in Germany

    Until they measure it or make a claim for the US light, I'm going to put:

    400 Lumens (mtbr estimate)

    It's certainly brighter than 270 lumens and it measures the same as several 400-500 lumen lights in my lux meter.

    fc
    Last edited by NiteBiker; 10-19-2011 at 05:29 PM. Reason: comparison with sigma light

  21. #371
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    Hey FC

    Did you publish the LUX readings yet. I didn't see it but maybe I missed something.

    And yes, you have to go out at least once w/ all the lights hooked up and at least 2 on the lid. With picts of course. It must just be laughable!!!!

    MB

  22. #372
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    Ok, serious winter commuter question:

    Which lights are going to be better for freezing or below temperatures, flash-light style or light head and external battery type?

    I commute 365 days, usually when I need my light is during the cold months, which are great for killing batteries. I had a Magicshine in the past and would use the extension cable to keep the battery in my jacket (close to my body). I have used a large cateye flashlight style as well with NIMH batts and that seemed to work out all right. But I want to hear from the experts.

    Flash light or lighthead and external battery for riding in the cold winter?

    Discuss! {:

    Or if there is a resource I have missed please direct me to the resource and ignore this post.

  23. #373
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    hey

    we have the opposite problem were batteries are killed by heat

    also this debate about whether lights hot to touch or not

    pretty simple i thought if light is that hot you cant touch while riding then its not doing that good a job of getting rid of heat

    so of course want a light that gets rid of it heat

    hot light it going to be heating up the internal meaning that light will have shorter life and run time since it cant get rid of the excess heat

    just from looking at some of the lights the real small ones being compact i think are going to have hard time of getting rid of heat unless they have good cooling design

  24. #374
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    Bueyin:

    I'm not sure where you are located, but I'm in Chicagoland, so hopefully similar weather. I haven't had issues with cold affecting light performance, but I'm definitely no expert and I pretty much stop riding outside when snow is on the ground. I have done quite a few night rides in cold weather down into the 20's and 30's, almost always 90+ minutes up to 2+ hours. I have noticed no battery degradation on my setup: Baja Designs Strykr bar light with external battery pack mounted on the frame + C8 or XM-L flashlight with 18650 battery mounted in a lockblock to either the helmet or bar. I pack spare batteries for the flashlight and usually get two rides in on the BD before re-charging. Not one to wear a jacket but the cord on the BD is long enough to make it to a jacket pocket if needed. My flashlights go 2+ hours before starting to dim, the BD well over 4 hours with mix of high medium lighting, could probably stretch that to 4.5 or 5 hours.




    Quote Originally Posted by blueyin View Post
    Ok, serious winter commuter question:

    Which lights are going to be better for freezing or below temperatures, flash-light style or light head and external battery type?

    I commute 365 days, usually when I need my light is during the cold months, which are great for killing batteries. I had a Magicshine in the past and would use the extension cable to keep the battery in my jacket (close to my body). I have used a large cateye flashlight style as well with NIMH batts and that seemed to work out all right. But I want to hear from the experts.

    Flash light or lighthead and external battery for riding in the cold winter?

    Discuss! {:

    Or if there is a resource I have missed please direct me to the resource and ignore this post.

  25. #375
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    Someone who you said is perhaps Mr.Olaf Schultz in Germany.
    He seems to have an integral sphere.
    So 291lm is not based on the current draw and the Luxeon Rebel LED specs.
    It is measured REAL lumen output from front of the light.
    His page and his measurement for Philips light.
    Fahrradseite auf www.enhydralutris.de
    LED-Bike Light Set BF48L20BBL

    And Philips claims that Philips SafeRideR LED batteriebetrieben is 270lm.
    Philips LED Fahrradbeleuchtung, Fahrradlicht ? Bike Light Batterie - Technische Daten

    But I also saw they described the same light as 220lm at somewhere, although I don't remember where it was.

    Quote Originally Posted by NiteBiker View Post
    I've read about somebody measuring this to be 291 lumens. Based on the current draw and the Luxeon Rebel LED specs, somebody else has estimated to be around 270 lumens. BTW, the philips webiste says "220 lumens on the beam", so that may be a honest figure taking into account optical losses? For a shaped beam like the Philips, lux (lumens per square meter) at a specified distance (e.g., 10m) makes more sense than lumens. It appears a *whole* lot brighter than the lumen spec suggests because it concentrating all the output on to the road. For example the Philips appears to illuminate the road better than the Sigma Power LED EVO 900 (claimed 900 lumens) and with superior throw as well!

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