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Looking for brightest LED on my new device

Discussion in 'Electronic Basics' started by iwico, Sep 30, 2003.

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  1. iwico

    iwico Guest

    Hi

    I designed a new kind of no battery flashing saftey lights for
    bicycles.
    see details go to my website: http://www.freelights.co.uk

    To save cost of magnets used in this device, the easyest way is using
    lowest voltage and current LEDs. I bought some (2 red rear LEDs in
    pictures on my website and one geen LED in front) LEDs from my local
    shop (London, UK). They said these are lowest voltage LEDs. All three
    LEDs are pallalet connected to the generator, working well but not
    bright enough.

    One day, I saw a new product from HongKong--(shake magnet inside the
    torch, lights a white LED in it for few minutes), I bought it and
    remove the white LED to replace the front green LED on my device.

    Now the white front LED is very bright, the rear red LEDs are not
    bright enourgh. They are powered by same device on my bicycle.

    Help:

    1. How do I find the white LED's details? such as: lighting voltage,
    current, name, and where to get it. (I did not ask the torch maker, I
    think they will not tell me this).

    2. Are there any red LEDs can bright same as white one on the market?

    3. What is the price of them.

    Thanks
    Q Gang
     
  2. LED manufacturers will have datasheets that tell you all you want to know
    (typical voltage and current, brightness, viewing angle, total light output,
    exact colour, etc.) There are many high brightness or energy efficient LEDs
    on the market. Typically on a bike safety light you want the widest possible
    viewing angle, which sacrifices brightness.

    The pitch given on your website is misleading. There may be no friction
    introduced by your system, but there certainly is drag! Small, but it's
    there. Also, the lights are only 'always on' if you are always moving, not
    the case at all.

    Adam
     
  3. cpemma

    cpemma Guest

    As you're in the UK I suggest you download the optoelectronics section of
    Rapid's catalogue at http://www.rapidelectronics.co.uk/.

    They do a good range, mainly Kingbright, & show KB code, spec values &
    prices (which aren't bad).
     
  4. All leds of a given color use about the same voltage, with bluer
    colors needing more than redder colors. What you need are high
    efficiency LEDS (most light per unit of current). The best way to
    know what you are getting is to read the manufacturer's data sheets
    and see what the efficiency is in lumens per amp or candela per amp,
    or some such unit. If you can't find the data sheets, go for ultra
    bright devices (but this adjective covers a huge range of actual
    efficiencies. But from a given manufacturer, their ultra brights will
    usually be more efficient than their run of the mill units.
     
  5. SNIPPED<<<

    Look more at the storage capacitor shake lights use as well
    As another poster suggested Rapid for Kingbright devices make a good red .
    Red tend to be cheaper than white 30p for an ultrabright, but shouldn`t be
    more than £1 for a good quality 5mm white LED, Nichia white LED may be a bit
    more expensive.

    HTH
    Adam
     
  6. Terry

    Terry Guest

    Congratulations on your experiments. And a suggestion.
    With two LEDs in parallel (even if they were identical which I
    gather they are not?), and depending on their specifications, one
    LEd may well have a lower resistance than the other and be using
    more current and be brighter? This is always a consideration when
    devices are in parallel.

    Brings back memories of my 'two light level' battery operated
    front lamp on my pedal bike. Any light at all was 'legal' as far
    as we could tell but the extra light was useful when crossing
    tram lines or avoiding water gratings!

    Also reminds me of someone at school who added a car battery and
    an electric motor to his (push bike). It worked fine; one way, to
    school. However he had to, rather dispiritedly, walk and push it
    home cos. the battery went flat.

    Two comments.

    1) Bicycle light generators of the type that do not rub against
    the tyre of the bicycle were used before the 1940s. One type
    looked very similar to the hub brakes used on some Humber brand
    bikes. The wheel hub was about four inches in diameter on one
    side and smaller on the other; different length spokes were used
    for each side of the wheel. The generator was always/usually on
    the front wheel because such bikes often had a Sturmey Archer 3
    speed hub gear (about three inch diameter) on the back wheel
    IIRC.
    A friend at school, in the 1940s-early 50s had an old pre W.W.II
    bike (a big black monster) that was equipped with such a hub
    generator. Humber bikes IIRC were made in Beeston Yorkshire?

    An interesting thing was that while anyone who had the type
    generator that impinged on the tyre, front or back wheel, but
    often front mounted because it was less cluttered than the rear
    wheel area, could feel the additional resistance/friction! But
    the hub generator 'appeared' to add no additional resistance. In
    our schoolboy fashion and discussion with the Physics teacher, we
    decided that the energy HAD to be coming form somewhere.

    BTW with front mounted, against the tyre, you could often reach
    down and click it away from the front wheel to reduce effort
    while pedalling, say up a hill, provided the police didn't stop
    you for no bicycle lights, front and back please!
    Nostalgic Question for iwco/Q.Gang: Are bikes still required to
    have front rear lights in UK?

    2) Back in those days LEDs, small but large farad size etc.
    capacitors, and piezo electric crystals that could generate any
    significant amount of wattage, had not been invented/discovered.
    However I do recall a hand held torch/flashlight which generated
    electricity by successfully pressing a handle on the outside (no
    batteries), whereupon the light would give light for a few
    seconds; I can definitely date that to around 1941-43.

    I finally went back to using batteries for my bike; the the rear
    (red) light required a single 'D' or U2 cell (at a cost of about
    sixpence or roughly one 40th of a pound which in those days was
    worth about 4 US Dollars). So $4/40 = roughly ten cents! I was
    fed up, that, in winter, when it got dark at about 3.30-4.00PM I
    had to buy TWO such batteries to get through the winter season!
    Would cost me ten times that in gas/petrol alone these days to go
    the same distance!

    So good luck with your experiment!

    Terry.
     
  7. You can use a standard bicycle dynamo to operate LED lights. Those
    generate about 6 V AC, a red LED needs 2 V DC. So if you take 3 LED in
    series, and another 3 also in series, anti-parallel to the first set,
    you have a very bright back light. Since white LED require about 3-3.5
    V, you would need 2 sets of 2.

    -->|-->|-->|--
    6V AC o--| |--o Gnd
    --|<--|<--|<--
    Front lights should be white, not green. In some jurisdictions you can
    get away with yellow, but certainly not green.
    Elector has a paper on ultrabright LEDs in this months issue.Also,
    catalogues from electronics suppliers like Maplin give you some info.
    Much brighter. My Conrad catalogue has red LED up to 20,000 mCd, whites
    are only 9,000. You may also consider the new Luxeon devices, which run
    at several 100 mA and produce very bright light. But read the technical
    specs carefully, at more than 10 GBP each you don't want to fry them
    The brighter, the more expensive, unfortunately.
     
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