How Do I Identify a Diode's Value?

By David Gitonga

Diodes allow conduction of electric current in one direction while blocking current from the reverse direction. Diodes come with colored stripes that help you read the value on the diode.

Reading the Stripes

Hold the diode with the separate colored stripe to the left. The stripe identifies the cathode, that is, the direction the current flows. In this position you can now read the stripes from the left going right.Identify the first and the second stripes if the diode has three stripes. If it has four stripes identify the colors of the first three stripes. Write them down.

Color Code Table

The color coding rating table below is used to identify the value of each color code:Black -- 0Brown -- 1Red -- 2Orange -- 3Yellow -- 4Green -- 5Blue -- 6Violet -- 7Gray -- 8White -- 9

Tolerance Rating

The last stripe (as long as there are 3 or less) is used to determine the number of zeros. For example, red, red, red will have a value of 2,200 ohms. A fourth band is an accuracy tolerance band. The tolerance rating is shown below:Gold - +/- 5%Silver - +/- 10%Compute by adding or subtracting the percentage to or from the value result of the three stripes.