What kind of LED?

Thread Starter

geosync

Joined Aug 13, 2008
9
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?
 

Audioguru

Joined Dec 20, 2007
11,249
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.
 
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Thread Starter

geosync

Joined Aug 13, 2008
9
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>
 

leftyretro

Joined Nov 25, 2008
395
"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
 

RiJoRI

Joined Aug 15, 2007
536
Tonic water will fluoresce under UV.
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
 

beenthere

Joined Apr 20, 2004
15,819
just a point of clarification. Leftyretro said;
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.
TV remotes and such us IR LED's, not UV.
 

SgtWookie

Joined Jul 17, 2007
22,210
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?
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]
 

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Wendy

Joined Mar 24, 2008
22,146
Something else to consider, Vf will tell you approximently when it was made. The older LEDs dropped less voltage than the new ones.
 

italo

Joined Nov 20, 2005
205
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.
 

Thread Starter

geosync

Joined Aug 13, 2008
9
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.
--Rich

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
 

Thread Starter

geosync

Joined Aug 13, 2008
9
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.
I love this! Thanks Wookie!
 
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