Coherent vs. Incoherent Light: Key Differences Explained

This article breaks down the differences between coherent and incoherent light.

Coherent Light

Coherent Light

• Coherent light is characterized by having a single, very specific frequency or a very narrow range of frequencies.
• To the human eye, it appears as a very pure, distinct color.
• Examples of coherent light sources include lasers and LEDs.
• As shown in Figure 1, coherent light waves are “in phase,” meaning their peaks and troughs align. This alignment causes the waves to combine constructively, resulting in a relatively high irradiance (intensity).

Incoherent Light

Incoherent Light

• Incoherent light, also known as noncoherent light, consists of a broad spectrum of frequencies and wavelengths.
• A common example is the light emitted by a traditional light bulb.
• Figure 2 illustrates incoherent light emitted by an incandescent bulb. These light waves combine with many different phases, leading to near cancellation and, consequently, a very low irradiance.

Key Differences Summarized

In short, the primary difference lies in the consistency of the light waves. Coherent light has highly organized waves, while incoherent light has disorganized and varied waves.