LED resistor basic wiring [closed]

Question

I am looking for a single bright LED light. I'm using:

• a red 5 mm LED
• a 5 V, 2.5 A AC adapter
• a 1 Ω resistor

It works, but doesn't seem very bright.

Am I correct or completely wrong? What is the best color LED and resistor to optimize output using the 5 V power supply?

Answer 1

For calculating the appropriate resistor, you need to find out the forward voltage drop of the LED, and its forward current rating.

These numbers are in the datasheet of the LED.

Different colours require different voltages, and Extra Bright LEDs may have different voltages and currents specified than their dimmer cousins.

A calculation example:

A typical red LED has a forward voltage drop of about 1.8 V.

You have a 5 V power supply.

Somehow, the difference, 5 - 1.8 = 3.2 V, needs to be dropped in a resistor in series with the LED, or the voltage across the LED will be too high, which can damage or destroy it.

Assuming a current through the LED (and therefore the resistor) of 20 mA (not an uncommon value), the resistor must be, using Ohm's law:

\$R = \large{V \over I} = \large{3.2\ \mathrm{V} \over 0.020\ \mathrm{A}} = \normalsize 160\ \Omega\$.

For 10 mA, that would be 320 Ω.

Anyway: the value of your resistor is much too low, and you have probably fried your LED, which would explain why it doesn't look all that bright.

As for colours: the human eye is most sensitive to a yellowish-green, but you can buy many colours of LEDs of various power ratings. Some require higher voltages than 5 V, though, because several LED chips are used.