Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Modulating super bright LEDs helpplease

  1. Oct 1, 2009 #1
    OK...I am a total noob when discussing anything electrical....I am more at home in the mechanical side of life. Sorry....lol
    What my project is...is I would like to replicate a modulating headlight from a motorcycle by using very strong, bright LEDs. I ride a bike and used to use the halegen bulb with a modulator and it worked extremely well. Using it, 7-8 out of 10 motorists would make eye contact with you as compared to 2-3 out of 10 when not using it.
    I am now using HID headlights and you can't modulate them as you know. I don't feel as safe without the modulating light on the front..
    So...my project is....modulating a set of very bright LEDs to simulate the halegen light used before.

    Can this be done and can it be restricted to a 2 1/2 inch round area?
    How would one go about designing this and making it happen? Again...I'm totally useless at this electrical excitment so please can you help.
    Is there a free to use program that may help in designing it? What LEDs are best to use?

    Thanking you in advance
     
  2. jcsd
  3. Oct 1, 2009 #2

    berkeman

    User Avatar

    Staff: Mentor

    To modulate them, you just turn them on and off. The circuit that drives the LED current will often have an enable pin, so you would just modulate that with a signal from some sort of oscillator or timer.

    Check out the National Semiconductor LED Driver Designer link on this page:

    http://www.national.com/analog/led [Broken]

    .
     
    Last edited by a moderator: May 4, 2017
  4. Oct 1, 2009 #3
    Thanks for the reply...can you suggest a super bright led or a collection that would do what I need done? Is there a specific type of LED that would do what I need better than others? Or...would a group generate the better light source to see? Like I said originally...I'm totally lost at this subject, any and all help would be greatly appreciated!
    Thanks again
     
  5. Oct 1, 2009 #4

    berkeman

    User Avatar

    Staff: Mentor

    I did a Google Images search on LED Lighting, and gots lots of sources and ideas for you:

    http://images.google.com/images?hl=en&source=hp&q=led+lighting&gbv=2&aq=f&oq=&aqi=g3g-m1

    You should be able to buy something at the Home Depot type hardware store that will work for your bike. They will have LED lighting fixtures and "bulbs" that you can choose from, along with current specs, etc. Then you can use/make a circuit like from the National Semi website to drive the LED thing.
     
  6. Oct 3, 2009 #5
    Another question about LEDs the super brite ones...What will flashing or modulating them do to their life span?
    Also..would it be best to make my own or buy a store bought light in this reguard?

    Thanks again
     
  7. Oct 3, 2009 #6

    vk6kro

    User Avatar
    Science Advisor

    I had never heard of this, but there are apparently stringent rules about how this should be done:
    http://users.snip.net/~WCLAMB/mod-law.htm

    The rate of modulation shall be 240 plus-or-minus 40 cycles per minute.

    The headlamp shall be operated at maximum power for 50 to 70 percent of each cycle.

    The lowest intensity at any test point shall not be less than 17 percent of the maximum intensity measured at the same point.


    And a whole lot more. It all makes good sense considering this is a road safety issue, but it does mean you really do need to just go and buy one if you want to stay legal.

    Seems like they vary the brightness at a 4 Hz rate but don't actually flash the light. They vary it between two brightness levels during daylight hours. Probably this is done by applying a square waveform to control a pulse width modulator.

    I don't think flashing a LED would have any effect on the lifespan of the LED except maybe to increase it. I don't think I have ever seen a LED die of old age or excessive use.
    They are generally very reliable.
     
    Last edited by a moderator: Apr 24, 2017
  8. Oct 4, 2009 #7
    Yes thanks for your reply.....it is a very difficult thing to replicate as to the letter of the law...Yes you can buy a modulating headlight and I did, but that only works on a halegen bulb not HIDs. So..I'm back to my request...can someone help a complete dummy design a circuit to replicate as close as possible, a modulating LED light??? Please.
    Remember the LED need to be very bright as to shine above the regular headlight on low.
    I'm not trying to sidestep the law so to speak...just want to be more visible for safety sake.

    Thanks again
     
  9. Oct 4, 2009 #8
    OR....design a modualtor to work a store bought LED...is that easier? If I buy an already maufactured LED light can you design a circuit to modulate it? I can build it...just not design it.....as long as you layout the parts etc.
    Thanks
     
  10. Oct 4, 2009 #9

    berkeman

    User Avatar

    Staff: Mentor

    What voltage does the halogen bulb take?
     
  11. Oct 4, 2009 #10
    12 volt...55 watt bulbs......I tried a 24 watt bulb and it wouldn't modulate it correctly and it wasn't bright enough...the 55 watt bulb uses too much juice for my bike to handle when everything else is added to it. This is why I'm thinking LEDs...
     
  12. Oct 4, 2009 #11

    vk6kro

    User Avatar
    Science Advisor

    You might need some more information.

    Pulse width modulation is a stream of very fast pulses that can be varied in shape.
    If they are mostly 12 volts with short 0 volt parts in between, the lamp will be very bright.
    If they have short 12 volt parts and longer 0 volt bits, then they will be dimmer.

    Your modulation system would switch between two brightnesses by changing this ratio of ON/OFF times about 4 times a second.

    It is possible this would work OK on some LEDs but some other LEDs would use a switching regulator to get good efficiency and this would not accept an input that was pulsing.

    So, you would need to ask if the LEDs used a switching regulator. It is very likely that a high powered LED system would use one of these.
    If it does, it may include provision for modulation, but otherwise, I don't think you will be able to do it.
     
  13. Oct 4, 2009 #12
    So..I'm guessing that it best that I buy a LED for this specific purpose and design it for that LED etc. So..I'm putting this back in your court I'm afraid.....suggestions and solutions???
     
  14. Oct 4, 2009 #13

    vk6kro

    User Avatar
    Science Advisor

    No, not really.

    You would have to ask around to see what is available.
    LEDs that are bright enough to use as substitute headlights are comparatively recent developments.
    Such LEDs that can also be used to be modulated? I really don't know what would be available.
     
  15. Oct 4, 2009 #14

    berkeman

    User Avatar

    Staff: Mentor

    So it sounds like you have a unit that pulses 12V to the lamp at a legal frequency, and you just need to find an LED array that can run off of 12V. As vk6kro says, LEDs run off of current at a fundamental level, but often LED arrays will be packaged as replacements for incandescent or CFL units. Have you tried a google search for 12V LED replacements? Often they come in compatible base configurations (just plug them into the fixture), but if not, all you would be left with would be re-wiring a new base into your existing pulsing/battery unit.
     
  16. Oct 4, 2009 #15

    berkeman

    User Avatar

    Staff: Mentor

  17. Oct 5, 2009 #16
    WOW...thanks for all the reponces.....not to sound 13(I'm 50 actually...lol) or anything but this is great!

    Hmmm...As for using the original modulating device...I think it somehow responds to wattage not voltage....? I don't know? But..I will bore you with history...I had it running on my regular highbeam of the headlight(55/80 headlight)IIRC...it worked great. Then I switched from Halegen to HIDs to get much better visibility at night. So...I find out that HIDs can't be modulated...no big deal untill I nearly got hit....didn't see me!... So I try and use a regular spot lamp off of a car using a 55 wattage halagen bulb, worked well but used too much juice from the bike's system. I then changed the wattage of the bulb to 24 watts....the modulator didn't flash the bulb hardly....very strange? So...I'm assuming it has a working wattage to stick between...? LEDs use so little wattage that I'm sure it would even register through this modulator if a 24 watt bulb doesn't do so well. Am I right? In theory at least?
    Those links do look great for LEDs to use...but I still need to modulate them if my unit won't work on so little wattages. That is what I'm after in the end... to save wattage use..and keep my modulator.
    I wish I could easily learn this electricity magic!!!! Damn!

    Thanks again
     
  18. Oct 19, 2009 #17
    for baclgroun d, I've been doing designs, consulting on LED matters for >25 years. The drivers for the 1700 led's on the Luxor hotel in Las Vegas were my design. Still working after 5 years this Christmas.

    Color LEDs of any power turn off/on in less than a microsecond to a few nanoseconds. Just modulate the current.

    The modern high efficiency LEDs cannot have a peak current much higher than the max continuous.

    In a current project I will be driving 350 ma LEDs at 500 ma peak 10% on at 60 Hz. The heat developed is essentially the duty factor times forward voltage times current.

    If you want fast total turn-off, have a current sinking shunt (a resistor will do), because the capacitance of these is high enough that there can be a faint afterglow. The shunt can be a few % of the peak value.

    Forward voltage of LEDs varies from 2.2 or so for red to 3.5 or so for blue or white, which is a blue LED using a phosphor to make the rest of the white spectrum.

    If you try to modulate white rapidly, the blue can modulate to over 1 mHz, but the white phosphor will glow with the average blue energy.

    My main preoccupation can be seen by googling "microlaunchers"
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Modulating super bright LEDs helpplease
  1. Help with AM modulator (Replies: 3)

  2. Super Basic Circuit Help (Replies: 12)

Loading...