Why doesn’t an LED bulb glow when the Polarity is incorrect?

LEDs, or Light Emitting Diodes, are a special type of diode that produces light when an electric current passes through it. What sets LEDs apart is their sensitivity to the direction of this current, known as polarity. In an LED, there are two leads: the anode and the cathode. The anode is the longer lead and cathode the shorter lead. Essentially, the flow of electricity in an LED must follow a specific path—from the positive lead (anode) to the negative lead (cathode).

Understanding LED polarity is crucial because connecting an LED in reverse, where the anode is linked to the negative side and the cathode to the positive, results in what’s called “reverse bias.” In this state, the LED won’t emit any light. This happens because the semiconductor material within the LED permits electrical currents in only one direction.

A relatable analogy is that of a car battery, which also has a positive and negative terminal, dictating the direction of current flow. If you mistakenly connect the negative cable to the positive terminal and vice versa, it could harm your battery. While the consequences of reversing LED polarity are generally less severe, it remains important to adhere to the correct polarity to ensure proper functioning.

If your LED fails to light up initially, think of it as a simple fix, similar to reconnecting the power supply cable in the opposite orientation; only when the wrong polarity is the issue. It’s worth noting that LEDs are not designed to handle substantial reverse bias voltages, making the correct polarity crucial when dealing with these diodes.

So, if you want your LED to glow, make sure to connect the anode (longer lead) to the positive terminal of your battery and the cathode (shorter lead) to the negative terminal. This will ensure that your LED is forward biased and will emit light when power is applied.