Second Radiation Constant

The hc/kB of Planck's law, the constant that turns colour into temperature.

Specifications & Metrics

symbol

c2

status

Exact — exact via h and kB in the 2019 SI

value

0.01438776877 m·K

Relative Scale in Constants

Core Principles & Analysis

• About 1.4388 cm·K, the numerator of the exponential in Planck's law.
• Pyrometers and colour temperature owe their calibration to it.
• Wien's displacement constant is its close algebraic cousin.