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Light transmitting material with LEDs: Advice needed!

  1. May 18, 2012 #1
    Hi, this is my first post here on the forum although I've been following some other threads recently.

    I'm currently working on a thesis project with a colleague of mine in which we are engineering a night time pacifier. We are at the moment trying to find a way to make the shield of the pacifier light up using as a light source a few LEDs that will need to be placed safely inside the cover of the pacifier (which is located at the back of the pacifier in the center of the shield).

    I've heard that PMMA material has excellent light transmitting properties so the idea is to use such a material around the edge of the shield. The material would have to be string or rod like in order to practically fit it at the edge with a thickness of a few millimeters to 1 cm.

    Now, my two main questions are:
    Is there such a material that will transmit light from the LEDs if they shine perpendicularly on the rod-like material. Since the material will be placed around the edge of the shield while the LEDs are at the center there is no way to direct the light from the LEDs through either end of the rod. The cover will have to be transparent off course (at least where the LEDs are meant to shine out) but will the light physically be able to travel through the rod, making it shine, from that 90 degree angle on the rod?

    Finally, is there such a material that is safe to use for children? It will have to be soft enough to bend and chew withought shattering baby teeth and on the chemical side I have been informed that the material should be PP and not PC.

    Any advice and ideas with the aim to solve this puzzle are much appreciated.
  2. jcsd
  3. May 20, 2012 #2


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    Hi, Ikigai;
    Welcome to PF. I have no knowledge in this field, and am severely inebriated at the moment, but I feel obliged to throw in a couple of comments anyhow.
    The first is to ask whether or not this has to be an LED project. It just seems that it would be easier to use a phosphorescent material that can charge up from ambient light during the day.
    That having been said, would it not be easier to place just one LED in the nipple part of the device and have the light radiate outward into the shield from there?
    I'm afraid that I have no idea of what PMMA is, nor can I quite follow your reference to rods. With no offense intended, that all seems to be an over-complication. The closest thing that lies within my knowledge base is that acrylic will transmit light in just about any way that you tell it to. My defunct local bar had a beautiful picture of a sailboat made from an edge-lit slab of plexiglas. Holes were drilled in from the edges, and where they terminated the light showed from the side.
    I suspect, though, that in order to soothe an undeveloped person a very soft and diffuse light would be desired.
    The other problem that I can see, at least from a legal standpoint, is that you would need to have a battery of some sort in there. That has to be poisonous, so would (I'll say FDA, since I assume that you're a Yank) approve such a thing? Maybe you could bypass that by incorporating a small piezoelectric generator into the nipple, so that the sucking action could power the device?
    Okay, I'm starting to ramble now. :redface:
    Catch you later.
  4. May 21, 2012 #3
    Not too comfortable laying out the whole idea here but LEDs will be necessary yes.

    Placing a LED in the teat of the pacifier is not allowed by european regulations (I'm from Sweden btw)...also you can emagine how easily a baby could bite down on the LED.

    PMMA is a a material that has great light transmittence...wikipedia has more info. Optic fiber is another example so the material I'm after doesn't necessaily have to be rod shaped. It could be like a "fishing line" as well if that makes sense. The main thing to consider is a practical way to fit it on the ende of the pacifier shield. Waiting on some optic fiber that I ordered. The trick will be to make it light up uniformly and not just at the ends of the fiber. I heard that sandpaper could do the trick.
    About the idea being overcomplicated I'm sort of inclined to agree and so maybe the porject will just use LEDs without any PMMA material. Would still light up the pacifier in the dark I mean. But I'd like to try this idea of mine if it's practical. Pretty sweet to have a shield lighting up at the endges. Could sell better too ;).

    The european as well as american safety standards allow for the use of a battery as long as it can be incapsulated and shut it without possibility of removal.

    This last idea of yours sounds really interesting actually. It would have to be a simple and easy to implement mechanism though. Practical enough to consider substituting the battery for it. Could you explain a bit more how that would work with the sucking? Would the air pressure charge it up? The generator would have to stay out of the nipple though and inside the back cover of the pacifier. Every electrical component has to be in that confined space.
  5. May 22, 2012 #4


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    Ikigai, I'm honoured that you gave consideration to my comments.
    I looked up PMMA as you suggested, and immediately realized that it is the exact same acrylic that I mentioned. I hadn't thought of a shield or rods being made of that for a pacifier, because it's extremely rigid. A pacifier really should be all soft and rubbery, unless you're growing a baby Rambo. I've used plastic fibre-optical filaments (about .1 mm), though, and they are very flexible. Embedding those into a transparent silicone or similar shield should be fairly simple.
    Regarding the sandpaper approach... that sounds a little off to me. Internal reflection/refraction is what makes an optical fibre work. Eliminating all of the cladding would just leave you with a pile of fishline. Back when they were just starting VR experiments, the control gloves used fibre-optic strands laid out along the tops of the fingers. Each had a scoring mark in the cladding at the joint positions. The tech was called "nicked fibre-optics". The amount of light that didn't make it through indicated that a joint was flexed because the scored cladding separated under flexation and allowed leakage.
    What crossed my mind, and might not be practical, is that something like PET might exhibit similar transmission characteristics, but is far more flexible. A disk of that, sandwiched in a silicone envelope, might give you some options. Perhaps acrylic can be formed thin enough to be that flexible? If so, then you should merely have to score the surface in some sort of grid or cross-hatch pattern. (I'm reaching on that, because I really don't know.)
    Safety-wise, it appears that you'll be fine as long as you keep both the LED and the battery out of the kid's mouth.
    The notion of a piezo generator was just an off-the-top-of-my-head suggestion, which I hadn't thought out at all. There were 2 different ways by which I thought that it might work. One, which is invalidated by your safety constraints, was that lip pressure acting upon the nipple radially might deform crystals embedded in the latex (or whatever) that the nipple is made of. Based upon the constraints, I fall back to "plan B". Since the nipple is sucked away from the base plate, a linear piezo system could be used to attach the two.
    That's all that I have for now. I'm just as drunk now as I was the first time that I responded, so I've about expended myself. Besides, I can't proceed without further input from you.
    I fully understand your reluctance to reveal too much. I have a few patentable things myself, which I can't afford to develop. There's no way that I'll mention them in public.
    Also, my profound apologies for assuming that you were a Yank. I find it incredibly insulting when someone does that to me (I'm a Canuck), but the law of averages suggested that you were.
  6. May 23, 2012 #5


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    And this clarifies the matter how? :confused:
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