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Thread: High brightness yet low heat LED

  1. #1

    Default High brightness yet low heat LED

    Hi, I'm working on a light project. If you guys can help me that will be great.

    1. Using 7.4v or 11.1v battery 2200mah
    2. Which led do you recommend I should use to obtain high lumen yet not dissipate too much heat or need a heat sink? If does, it'll just be the copper it sits on and small metal casing...
    3. Should I regulate the current to reduce the heat?
    4. Need something small and compact, one emitter.
    5. What's the newest and latest led?
    6. Is dome better than flat? I plan to place optics over it to concentrate the beam.

    Thank you.


  2. #2
    Flashaholic* Keitho's Avatar
    Join Date
    Jun 2017
    CO, USA

    Default Re: High brightness yet low heat LED

    Wow, big set of questions. A little more info might help the quality of the answers: intended use, how much brightness (lumens or intensity or both) is required, and how much runtime is required out of 2.2 mAh (I assume that means either 16 Wh or 24 Wh?)

    At the low-brightness/low-heat/long-runtime end of things, one to three 5mm LED, with a small resistor (extra points for a variable resistor), direct driven from a battery would draw very roughly .1-.2W (and produce almost no heat) while producing 5-30 lumens; as the battery voltage drops, the brightness would drop, but it would be dead simple to make. At the high-brightness end of things, a full-featured flashlight driver with current regulation and temperature control, driving an LED soldered or otherwise heat-sinked to a metal casing could plausibly produce a sustainable many-hundreds of lumens without melting stuff; count on between 100-250 lumens/W (so, a 500 lumen LED or LED array might draw 2-5 W from the battery). The amount of heat produced by the driver is usually roughly related to how much it has to buck or boost the voltage; so, match the LED voltage as close as possible to the battery to reduce driver heat. The amount of heat the LED produces is a feature of the LED design--the more power it draws, the more waste heat is produced. A high-CRI, warm LED will generally produce fewer lumens/W (and usually, therefore, more heat for a given brightness) than a low-CRI, cool LED; but, use case will determine if color temp and CRI are helpful or not.

    LED array design can help spread heat out a little. You want a single LED, but a triple- or quad- or 10-LED array might be easier to dissipate heat than a single-LED of the same brightness. But, the intended use will dictate where you want those lumens to go. A key part of light efficiency (and therefore heat and power management) is to put the lumens where you want them, and nowhere else. Depending on use, optics or a reflector may help to shrink the power required.

    That wasn't a complete or specific answer, but I hope it helps!

  3. #3
    Join Date
    Jan 2020

    Default Re: High brightness yet low heat LED

    All good questions. We may want to start the design with more specific goals. That being said the latest Cree ledís are the XHP series. The XHP stands for extreme-high-power. XHP-35 size is 3.45mm x 3.45mm with a 13w power consumption rating and up to 1833 lm. XPH-50.2 is 5.0mm x 5.0mm with a power consumption rating of 18w and up to2654 lm. The largest of the series is XHP70.2 at 7.0mm x 7.0mm with a power consumption rating of 29w and up to 4292 lm. Remember the greater power consumption rating will give you more heat dissipation issues to consider. Trimming the led dome flat will give a more focused beam but there are a lot of other factors that will affect the final outcome. Once you have settled on the led that is best for the project the design can work can be developed around that choice. Enjoy and have fun!

  4. #4
    Flashaholic* DIWdiver's Avatar
    Join Date
    Jan 2010
    Connecticut, USA

    Default Re: High brightness yet low heat LED

    Unfortunately, you have some conflicting goals, so you'll have to make some tradeoffs (no surprise there).

    For the lowest heat generated for a given amount of light, you want the highest efficacy possible. This is in lumens per watt, or lm/W. For white light with good CRI, a perfect conversion of electrical power into light would result in around 340 lm/W. This number varies some based on the spectral properties of the light, but this is a good starting point. If you had an LED with 170 lm/W efficacy, that would be getting about half the possible output in light. The rest is converted to heat. If the efficacy is higher, you get less heat, and vice versa.

    For a tight beam with long throw, you want the smallest possible emitter surface. Ideally you'd have a point source, but that's physically impossible. The reason people de-dome LEDs is that the dome makes the emitter surface appear larger. This means it doesn't work as well with lenses. De-doming reduces the efficacy, but the improvement in optical performance more than makes up for it if your primary goal is long throw.

    Also, high efficacy tends to go with high color temperature (cool white) and low CRI.

    You shouldn't necessarily be looking for the latest thing that's been released, as it may not be optimal for your application. The latest, highest efficacy things that I've seen are multi-die arrays that wouldn't be suitable for a flashlight.

    Hope that adds a little to the conversation.

  5. #5

    Default Re: High brightness yet low heat LED

    Thank you so much you guys. Very helpful feedbacks. I want to keep it tiny, compact as possible with medium heat and bright led.

    3 watts or 5 watts or 10 watts.

    As for the led, will the hp35 function with a 7.4v or will it need 12v?

    If the higher the voltage, would that mean higher heat or does it depend on the current? If we restrict the current or add resistors, will it control the heat?

    I have a couple components that I need to attach to the system such as a battery indicator lcd unit and I believe it needs at least 8v or 12v to function...

    Also, here is an off the shelf unit I am trying to analyze. Can you tell me what led this is? I dont think it's a cree.

    Thank you for your expertise. Much appreciated.

    Hmm how do I add a photo?

  6. #6

    Default Re: High brightness yet low heat LED

    Here are the photos of the LED I am trying to figure out. What brand do you guys think this is? Thank you.

  7. #7

    Default Re: High brightness yet low heat LED

    Hope to hear from you guys soon. Thank you for your expertise and help.

  8. #8

    Default Re: High brightness yet low heat LED

    Quote Originally Posted by Travis2020 View Post
    Hope to hear from you guys soon. Thank you for your expertise and help.
    Hi, can anyone identify the led emitter brand in the above photos? Thank you!

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