Doppler Shift (Light)

\frac{\Delta\lambda}{\lambda} = \frac{v}{c}

Approximate Doppler shift for electromagnetic waves when v << c.

Variables

Δλ

Wavelength shift

Change in wavelength

Rest wavelength

Original wavelength

Relative velocity

Source-observer velocity

m/s

Speed of light

≈ 3×10⁸ m/s

Allowed values: greater than 0

m/s

Derivation

Non-relativistic approximation of relativistic Doppler formula. Positive v = receding (redshift).

Your notes

0/5000

Constants in this formula

Speed of Light in Vacuum

299,792,458. Exact by definition.

m/s

Where this formula is listed

Waves formulas, under Doppler Effect, alongside Doppler Effect (Approaching) and Doppler Effect (Receding).
In the waves list it comes after Doppler Effect (Receding) and before Standing Wave on String.
Waves formula sheet, one of 37 formulas printed with symbol keys and SI units.
The full formula index, grouped by category and topic.

Common questions

What is the Doppler Shift (Light) formula?

Doppler Shift (Light) is written Δλ/λ = v/c. Approximate Doppler shift for electromagnetic waves when v << c. It belongs to Waves, under Doppler Effect.

What are the units in Δλ/λ = v/c?

In SI units, Δλ is wavelength shift, measured in m; λ is rest wavelength, measured in m; v is relative velocity, measured in m/s; c is speed of light, measured in m/s.

How is the Doppler Shift (Light) formula derived?

Non-relativistic approximation of relativistic Doppler formula. Positive v = receding (redshift). The result is Δλ/λ = v/c.