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Thread: white LED's and mcd values

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  1. #1
    Enlightened spaspeckerthedull's Avatar
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    Default white LED's and mcd values

    I'm currently in the middle of a lighting project and am new to the LED game - I've read about as much as I can find about LED brightness but it's just not going in anymore!! I am lighting a plastic rod bent into a semi circle using LED's at either end and need to be able to see it in the daylight - I have considered using a CCFL but these are

    a) too brittle
    b) don't come in the size that I need

    I've been using various LED's over the last few weeks with different outputs and haven't really come up with a satisfactory light output. So far I've tried 5mm 20kmcd, 5mm 55kmcd and 5mm 100kmcd. I've also tried using a luxeon 1watt 40lumen led fitted with a reflector to focus the output in a lightbox and feeding the light into the ring at either end with an end emitting 6mm fibre optic cable. I have seen some 8mm white LED's advertised as outputting 280kmcd and some more that claim 60lumens?!?

    any ideas?
    whistling on a tuesday jester

  2. #2

    Default Re: white LED's and mcd values

    What, are you trying to use the rod as a clear plastic "light pipe" then?

    Seeing things in daylight may require a LOT of power depending on the exact viewing conditions. In the direct afternoon sun, the power required to overwhelm the ambient light would be tremendous. It could melt the plastic.

    mcd is a measure of the light flux per degree. So a 20kmcd, 55kmcd or 100kmcd might be the exact same emitting die. Tighter focus yields more mcd. LUMEN is the actual unit of total emitted light power.

    Traditional 5mm T1-3/4 LEDs have very limited optical power; the package can't dissipate much heat. The best of the best 5mm LEDs may be like 5 lumens (used to be 1 lumen when all the Photon microlights rage started). Luxeon Star and other stuff has VASTLY greater lumen output.

    Best emitters are like 100 lumen/watt now. You can get more light than 40lumens.

    If I understand correctly that you're feeding a light pipe, most likely you have a problem with how much is actually being captured here.

  3. #3

    Default Re: white LED's and mcd values

    I am no expert and not even competent in these matters but have some ideas or comments none the less. To get the light into the plastic rod, I suspect it needs to enter reasonably close to perpendicular in angle to the end of the plastic? If this is the case, unless the plastic has a scuffed or frosted surface, most light will likely reflect internally and not exit the sides. You might want to do some simple bounce testing in a dark room and see how much light you get in the room from the LED's alone and then when mounted up to the plastic.

    How efficient is your plastic rod at diverting the light you feed it?
    Build Prices .... some mods and builds (not 4 sale) "Nature can be cruel- but we don't have to be."~ Temple Grandin

  4. #4
    Enlightened spaspeckerthedull's Avatar
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    Default Re: white LED's and mcd values

    plastic rod is scored along the back allowing the light to leak out, also it doesn't necessarily have to be 5mm LED, I could probably go up to about 10mm. I know about the luxeon/lumiled throwing more lumens out, but that would mean buying another more powerful LED AND another driver to drive it as the one I've already bought is rated at 1watt to match the LED. Cost is a factor but I don't want to be shelling loads out as at the moment it still is a project. The plastic rod I'm using has a diameter of 6mm, the LED's are secured at each end of the rod and are pointing towards each other. That's why I'm looking at the 8mm LED's as they are advertised as 1watt 140degrees 60lumens at 300ma (these are NOT lumiled/luxeon) I'm also considering 10mm 0.5watt multichip 40degrees 280kmcd. Also, bright sunlight is not really a consideration, just fairly visible in daylight will do
    whistling on a tuesday jester

  5. #5

    Default Re: white LED's and mcd values

    It doesn't help with the "cheap" part of the equation, but what you need is one or two Cree XR-E LEDs fitted with light-collimating lenses that are designed for "insertion" into fiber optic bundles.

    You mentioned a reflector, but your goal needs to be focusing ALL the LED light into a "point source" at the end of the plastic rod at a perpendicular angle to the rod end, if your LED is facing forward (even with reflector) with nothing collimating it, most of the LED energy isn't coming close to the necessary angle and concentration to "insert" into the rod.

    The proper collimating lenses for fiber optic insertion (which will work for this application as well, it's just a REALLY oversized fiber in this case), are only a few dollars, the LED and lenses can probably be bought for $15-20 (plus shipping of course). A single LED will work with your 1W driver, but for best results you'd double them up, put one at each end of the tube, and drive them at around 3W to get a good brightness/efficiency compromise (assuming you deal with the cooling issues appropriately).

    You also need the "ends" of your plastic rod to be polished as smoothly as possible, EXTREMELY smooth... get some very smooth paper, coat with jeweler grade lapping compound, lay on top of a piece of glass, and polish the end for awhile (figure 8's is the fiber optic pattern)... it won't be perfect without a way to hold it vertical, but good enough for this usage probably.

    The Polymer Optics part # is 173, for an example of what I'm referring to. The only way I can imagine to do it well with a reflector would be to fire the LED backwards (into the reflector) and let the reflector focus the beam back down to a near-point source for beam insertion. Or remove the silicon dome from the LED (not highly recommended as it's likely to break the LED, but it can be done) and mount the LED nearly flush with the end of the plastic rod. Most of the light from the LED die is emitted "vertically" anyhow, so this would probably have pretty good results.

    Anyhow, have fun!

  6. #6
    Enlightened spaspeckerthedull's Avatar
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    Default Re: white LED's and mcd values

    Quote Originally Posted by Christexan View Post
    It doesn't help with the "cheap" part of the equation, but what you need is one or two Cree XR-E LEDs fitted with light-collimating lenses that are designed for "insertion" into fiber optic bundles.

    You mentioned a reflector, but your goal needs to be focusing ALL the LED light into a "point source" at the end of the plastic rod at a perpendicular angle to the rod end, if your LED is facing forward (even with reflector) with nothing collimating it, most of the LED energy isn't coming close to the necessary angle and concentration to "insert" into the rod.

    The proper collimating lenses for fiber optic insertion (which will work for this application as well, it's just a REALLY oversized fiber in this case), are only a few dollars, the LED and lenses can probably be bought for $15-20 (plus shipping of course). A single LED will work with your 1W driver, but for best results you'd double them up, put one at each end of the tube, and drive them at around 3W to get a good brightness/efficiency compromise (assuming you deal with the cooling issues appropriately).

    You also need the "ends" of your plastic rod to be polished as smoothly as possible, EXTREMELY smooth... get some very smooth paper, coat with jeweler grade lapping compound, lay on top of a piece of glass, and polish the end for awhile (figure 8's is the fiber optic pattern)... it won't be perfect without a way to hold it vertical, but good enough for this usage probably.

    The Polymer Optics part # is 173, for an example of what I'm referring to. The only way I can imagine to do it well with a reflector would be to fire the LED backwards (into the reflector) and let the reflector focus the beam back down to a near-point source for beam insertion. Or remove the silicon dome from the LED (not highly recommended as it's likely to break the LED, but it can be done) and mount the LED nearly flush with the end of the plastic rod. Most of the light from the LED die is emitted "vertically" anyhow, so this would probably have pretty good results.

    Anyhow, have fun!
    I think I get what you're saying, but something I forgot to point out is that space is an issue - when I went down the 1watt luxeon lightbox fibreoptic route it's because that's the only way I can feed light generated this way into the end of my plastic rod, what I've been doing with the 5mm LED's is heatshrinking them onto the end of the rod so they are actually perpendicular to the cut section but as mentioned I can probably go a size bigger. BTW I'm in england, so stuff for a project like this over here is neither readily available or cheap but I am appreciating the input! basically I need to light my plastic rod as bright as I can for as cheap as I can!!!! just for example, the fibreoptic I bought was 1meter and it cost £13:50 sterling - that's about $25US (I think)

    has anyone any experience of the 60lumen 8mm LED's I mentioned? I can post a linky but it might not work?


    http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=011

    opinions please?
    whistling on a tuesday jester

  7. #7
    Enlightened spaspeckerthedull's Avatar
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    Default Re: white LED's and mcd values

    whistling on a tuesday jester

  8. #8

    Default Re: white LED's and mcd values

    I got 50 of those 10mm, 280,000 mcd and they rock. There are 5 LCDs in one, you can see the leads while focusing on the ceiling with a magnifing glass.

    Then I'd do Cristexan's idea times 2 -

    File 1/4" of the 10mm LED to 6mm dia. and polish the end of the LED too! (so cut the end flat first, where it's 6mm)

    Fold 600 grit sandpaper over something very thin and very flat and clamped to the table or something, and do both 'ends' at once (one on each side - LED on one and rod on the other) then even if they end up a little angled, they'll still line up perfectly. Now to polish(Dont laugh till you try it for 60 secs.) TOOTHPASTE! Take the sandpaper off and lube up your flat thing!

    Now that your rod and 2 LEDs are almost a single piece of plastic... Be real careful attaching everything, no glue on faces! (There's probably a glue made just for this purpose, but it's not in my head) Epoxy on sides? 8-10mm crimped brass rings, both?

    Now dangit... Out surfin, and now I'll be building this thing! (What is it again?)

    -Cy

  9. #9
    Enlightened spaspeckerthedull's Avatar
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    Default Re: white LED's and mcd values

    I see where you're going with this, but if I file the end of the LED down won't that widen the angle? I thought that if I wanted as much of the emitted light as possible to travel forward I would need a narrower angle? can someone advise me of this?
    whistling on a tuesday jester

  10. #10
    *Flashaholic* Gunner12's Avatar
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    Default Re: white LED's and mcd values

    IIRC there were optics designed so as much light as possible from a high power LED like an old Luxeon(unless if it's a Rebel or TFFC K2) goes into an optic. The Cree XR-E and Seoul P4 are both at least twice as efficient(twice the output for the same power) as the Luxeon I, III, V, and K2s. I don't remember where I saw the optics though.

    How wide is this plastic tube?

  11. #11
    Enlightened spaspeckerthedull's Avatar
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    Default Re: white LED's and mcd values

    the plastic rod has a 6mm diameter, but my main problem still is if I were to use something like a cree, or a lumiled, or a p4 or whatever the only way for me to feed the output into the rod is to use a fibre optic. I have purchased an end emitting fibre optic (at great cost) which also has a diameter of 6mm (it is a single fibre, NOT a multi strand) but I still need some guidance as to how to feed my generated light into the rod - hence my original question concerning a "normal" or "conventional" shaped LED and its output as these are much easier to fasten to the end of a rod. I have no qualms in going down the lightbox/fibre optic route but am still puzzled as to how I would channel all the p4 light output through the fibre into the rod

    BTW guys - great ideas/support/questions, keep 'em coming!!
    whistling on a tuesday jester

  12. #12

    Default Re: white LED's and mcd values

    The 5 dies are all in a dome that's less than 6mm. It looks more like 4mm. I just think Christexan is on it. Polishing would eliminate any obstruction.

    Taking the sides down to 6mm isn't important, making them the same size as the rod was a way to attach it is all.

    You made me think with your reply, somehow silvering everything except the polished part on the LED might help. Silver leaf? (AFTER insulating the bottom! ) (Did I just make version of a light box?)

    Mounting with clear heat shrink tubing or clear epoxy would eliminate doing anything to the 10mm LEDS except flattening and polishing the top to at least 6 mm.

    Apologies for not introducing myself the first time...
    HELLO EVERYONE!

    I missed your next post when I posted this, now I'm lost. It's been a couple years since I posted on a forum and it surely shows! LoL

    I did wanna warn anyone thinking of buying a quantity of those 280k mcd's on eBay, they're very pricey as of 3-4 days ago. I got 50 6-8 months ago for less. Maybe $10 less. I also noticed the other day that the common cathode rgb's are nuts too, they're double what I paid.

    Good Luck!
    Last edited by CyCo; 08-08-2008 at 10:50 PM.

  13. #13
    Enlightened spaspeckerthedull's Avatar
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    Default Re: white LED's and mcd values

    for mounting the LED's I've been using some clear fish tank tube with a 5mm internal diameter, just put it in some hot water to make it supple then slip about 10mm over the end of the rod, cut it off with about another 10mm protruding off the end of the rod and the LED slips inside it a treat, then cover the whole thing with heatshrink to tidy up and seal. I tried experimenting with silver cooking foil under the heatshrink but it didn't really make much difference, that's why I'm trying to find a powerful LED hence the 8mm ones I've seen that are advertised at 60lumen @300ma, but the 140degrees is worrying me - or should it?

    OK guys - it's real late here now so I'll pick this up again tomorrow, thanks for the input and keep it up!!
    Last edited by spaspeckerthedull; 08-08-2008 at 05:38 PM.
    whistling on a tuesday jester

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