leds

[shermaine]

how to determine the forward bias voltage for red, green, blue led?

 

[Papabravo]

A resistor, an ammeter, a power supply and a voltmeter.

 

[Gayan Soyza]

Take a variable DC supply that starts from about 1.5V & give to the LED. You won’t see it lights up. Now slowly increment the voltage & see what voltage the LED starts to lights up. That’s the voltage you looking for.

 

[audioguru]

LEDs operate with current, not voltage.
You must use a current-limiting resistor in series with the LED so you don't use too much current.
Then simply measure the voltage across the LED.

 

[Hero999]

Simply connect the LED in series with a resistor and connect it to a power supply and measure the voltage across the LED.

 

[kchriste]

The easiest way is to read the data sheet.

 

[audioguru]

The easiest way is to read the data sheet.

It will say the range of forward voltage. If it is a red LED it will say "minimum= 1.5v and maximum= 2.4V at only 20mA".
You must measure it to know what is the actual forward voltage.

 

[Optikon]

Some typical forward voltages for various LEDS

All data @ ~ 10mA forward current

I.R. = 1.40V
Red = 1.65V
High-Efficiency RED = 2.20V
Pink = 2.00V
Orange / Amber = 2.10V
Yellow = 2.20V
Green = 2.20V
High-Efficiency Green = 2.30V
Blue = 3.10V

These are *TYPICAL* values.
These values will differ from vendor to vendor.

 

[Krumlink]

Ive never seen a pink LED. What are the voltage ratings for Organic LEDs?

 

[Ambient]

The LED's I got from moreleds.com are:

Blue: 3.3V
White: 3.3V
Red:1.7V
Green:1.7V

all were ultrabright LED's, more than 5000mcd.

The other site to check out is: **broken link removed**

 

[Optikon]

The LED's I got from moreleds.com are:

Blue: 3.3V
White: 3.3V
Red:1.7V
Green:1.7V

all were ultrabright LED's, more than 5000mcd.

The other site to check out is: **broken link removed**

Interesting.. what current were they measured at?

 

[audioguru]

Cheap LEDs are very bright when the plastic case makes a very narrow angled focussed beam from a dim old LED chip.

Good LEDs are wide angle and very bright.