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

Optics Help With LED Foglights

  1. Nov 5, 2008 #1
    well i have been working on this project for a while now. i want to create an led retrofit for my foglights. every idea i have stumbled upon, i have found faults with. my main concern is functionality. i want these to look good AND serve a purpose. for example, i have found pictures of a BMW that a guy placed 30 super flux leds per side in. you can see from the pics that there is an extreme amount of glare and light bouncing everywhere. you can also see on the wall shot how the halogen bulb has more "throw."

    [​IMG]
    [​IMG]
    [​IMG]

    then me and a friend of mine came up with this idea. we thought that we can use a projector housing and mount the leds on the cutoff shield facing the back of the housing.

    [​IMG]

    i semi-tested this idea out. but i placed the led at the back of the projector, where the hid bulb would normally go in at, and have the led shine outward. it created a weird output. it was too difficult to even put the led inside much less, mount them on the cutoff shield.

    [​IMG]

    so this is where im needing help. the only other plan would to be make the housing itself into a projector. i mean to take the oval housing i currently have, and make a cutoff shield to mount on it. then mount my leds on the back of it in my original plan.

    here are pics of the stock foglight housing.

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]


    just to give an idea here, if im not mistaken halogen bulbs create 1200lm, hids create 1700lm, and i would say the BMW in the pictures above would be 40-50lm. i found leds that i would like to use. i would put 2 leds per foglight at 750-800lm each. should be nice and bright if i can take advantage of all that light and focus it down and outward instead of just bouncing everywhere.

    any help or suggestions would be greatly appreciated!
     
  2. jcsd
  3. Nov 6, 2008 #2

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor

    Lighting (that is, non-imaging light projection) has become a very specialized field now-partly because the use of plastics greatly expands what can be done.

    I'm not an expert, but hopefully you can see that the foglight has a very complex reflecting and refracting geometry- all those features (the ridges, the shape, etc) are designed very carefully.

    My suspicion is that the LED bank didn't work as well because the sources were no longer located at the same location as the halogen/arc; this means the optics need to be re-designed to take into account an extended source rather than a localized source. Finally, LEDs have a different radiant emission pattern than a bulb.

    In addition, auto manufacturers have a lot of non-optical specifications to meet: how well the materials hold up in poor weather conditions, for example.

    I suspect that you are best off with an 'engineering approach'- try different things, see what works best, then refine the design further. There are optical design programs that can handle nonimaging applications (OSLO is the big one, I think), but I haven't used it and don't have the time to learn how.
     
  4. Nov 6, 2008 #3
    thank you for your response. the reflective housing is one of my big concerns. i believe that is a catalyst to my glare problems but reflecting the light everywhere. i have had ideas of painting that housing a flat black as well. i think that by doing that, it should help significantly but it will not solve the problem at hand.
     
  5. Nov 6, 2008 #4
    ok ive been throwing some of these ideas at my friend here
    and one thing i think that really hasnt been checked is how the projector would handle the lightoutput from the bottom, if someone has access to that program, that would be awesome, otherwise field testing will happen sometime in the comming months
    im pushing this because of those SSC 900 lumen leds, 90 lumens per watt!
    yes it would be 40 watts for 3600 lumens, but it would be an led

    while he is worried about heat, im not as much as these are going to be thermal glued to the back of the cutoff shield on a projector

    otherwise, the next step is some sort of plastic lens that will give a similar light output that a projector would

    ideas would be appreciated!
    sorry to hijack the thread man :-p
    oh and dude, im pretty sure that 4 of those leds would NOT fit in a small projector assembly, only a full size one
    BUT you can proly fit two WITHOUT the stars
    but thats saying that the optics work, which im starting to doubt lol
    someones gotta have some ideas!
     
  6. Nov 8, 2008 #5
    anyone? or can someone point me in the direction of help?
     
  7. Nov 8, 2008 #6
    You are into a speciality area where experience is likely critical..
    Have you tried searching LED lightning design....I got a LOT of websites,
    see what's available and what others have done....e-mail a few companies
    which seem interesitng and relevant.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Optics Help With LED Foglights
  1. Help with optics (Replies: 6)

  2. Refraction optics help (Replies: 1)

Loading...