What kind of LED?

Discussion in 'General Electronics Chat' started by geosync, Feb 3, 2009.

  1. geosync

    Thread Starter New Member

    Aug 13, 2008
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    I got it in an LED grab bag. It's clear (no color) out-of-circuit, but glows red when in-circuit. Is this a special kind of LED?
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    Nobody knows the spec's or ratings of an LED made by "No name Brand".
    I hope you got them for free.

    Most cheap LEDs are old dim ones in a focussed plastic case that makes them appear bright because the light beam is very narrow. Modern bright LEDs have a wide angle of light.
     
    Last edited by a moderator: Feb 9, 2009
  3. geosync

    Thread Starter New Member

    Aug 13, 2008
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    Hmmm...ok then. They come on when I forward-bias them, which is about all I need right now. Thanks.

    Before posting my question, I wondered if it was UV, an LED type that I haven't experienced yet. Which leads to another question; this time about UV LEDs:

    How do you know if a UV LED is on?

    I thought maybe it'd be a good idea for the device to release some visible light AND UV, so you could tell it was on. <g>
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    Pointless post deleted by moderator
     
    Last edited by a moderator: Feb 9, 2009
  5. thingmaker3

    Retired Moderator

    May 16, 2005
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  6. leftyretro

    Active Member

    Nov 25, 2008
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    "How do you know if a UV LED is on? "

    Most digital cameras will display UV LEDs in their displays when pointed at the LED. Mine did when I pointed the TV remote to it and pushed buttons of the remote.

    Lefty
     
  7. RiJoRI

    Well-Known Member

    Aug 15, 2007
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    So, has anyone designed a glass with UV lights in the bottom??? :D

    As a child of the 60's, I remember we used to turn off the white lights, and turn on the UV. Lint on dark pants would brightly glow, providing a bit of amusement.

    I have one or two of those clear plastic - glows red LEDs in my stuff. As far as I know, it's just a red LED with a voltage drop of 1.4 VDC. Caveat emptor: YMMV.

    --Rich
     
  8. thingmaker3

    Retired Moderator

    May 16, 2005
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    Don't know... but my young padawan made a bottle with UV LED under the stopper.:)
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    just a point of clarification. Leftyretro said;
    TV remotes and such us IR LED's, not UV.
     
  10. bertus

    Administrator

    Apr 5, 2008
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  11. leftyretro

    Active Member

    Nov 25, 2008
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    Well at least I thougt I read IR :rolleyes: Just too many darn names for all those various parts of electromagnetic spectrum.

    Lefty
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    In the old days, LEDs were cast in a plastic that was colored to block the off-spectrum light. Red LEDs were red, green LEDs were green, etc.

    Nowadays, many LEDs are available in packages that have no color (clear) until the LED is lit. The chemical formulation of the LED controls the color that is emitted, rather than the encapsulating plastic.

    With "grab bag" LEDs, you'll never know what you're actually getting. Most of them will be safe to operate at 20mA. You can create a 20mA constant current source by using a 62 Ohm resistor and an LM317 voltage regulator to help you sort out your LEDs, and determine their Vf's (forward voltages) in conjunction with a digital multimeter (cheap nowadays).

    Connect the 62 Ohm resistor from the OUT terminal of the LM317 to the ADJ terminal. Connect a 7v to 12v source to the IN terminal. Connect your LED from the ADJ terminal to the return path (ground). Measure the Vf across the LED.
    [eta]
    [​IMG]
     
    Last edited: Feb 6, 2009
  13. Wendy

    Moderator

    Mar 24, 2008
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    Something else to consider, Vf will tell you approximently when it was made. The older LEDs dropped less voltage than the new ones.
     
  14. italo

    New Member

    Nov 20, 2005
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    I am not chinese far from it. But i know that many manufactures use china cheap labor to make all kinds of things. China manufactures the same LEDS used here HP,GEjust put their name on it. What we expoing right now? debt,lawyer and baseball player. I remenber NAFTA 500 people lost their jobs why not cost /worker was $45/hour Mexican workers $5 a day. We are capitalist and must pay the piper. We need 700 billion dollars no problem just print the money. We do it so is everyone else keeping status quo. My HP computer is made in MEXICO WITH AN HP LABEL. Need help with it sure get it from INDIA.
     
  15. geosync

    Thread Starter New Member

    Aug 13, 2008
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    I don't believe you, Rich... If you remember the 60s, then you weren't there. :D

    btw, for those who are curious, the LED came in a grab bag I bought from Electronix Express.

    Rick
     
  16. geosync

    Thread Starter New Member

    Aug 13, 2008
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    I love this! Thanks Wookie!
     
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