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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?

enter image description here

ocrdu
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Jerome Lowery
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    what does `optimize output` mean? ... read the datasheet for the LED ... there should be some graphs that show the relation between current and luminosity – jsotola Nov 20 '20 at 18:51
  • One ohm is much too small. Can you draw out how you've wired it up? – td127 Nov 20 '20 at 18:52
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    The LED is most likely broken already. You need much larger resistance than 1 ohms to do this. And some data about the LED how much current it is rated for. Assumption is 20mA unless there is some evidence it can take more. – Justme Nov 20 '20 at 19:07
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    Data sheet, data sheet etc... – Andy aka Nov 20 '20 at 19:27
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    1 ohm resistor is a value so low that, in that circuit, it could burn the LED. Are you sure that this resistor is 1 ohm? Isn't it 1 K ohm? Are you able to read resistor's color code? What are the color bands in the resistor? – mguima Nov 20 '20 at 19:47
  • Your wiring diagram looks good. Make sure the ground side of your power supply connects to the cathode of the LED, which is denoted by a flat edge in the plastic. The other lead goes to a resistor in the 100-500 ohm range and then to the 5V. – td127 Nov 20 '20 at 21:11

1 Answers1

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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.

ocrdu
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