We describe a simple near‐infrared hygrometer based on a broadband light‐emitting diode (LED) centered at 1320 nm. Light from the LED is collimated and passes through a rotating optical‐filter assembly and a sample cell. The water vapor concentration is measured using a synchronous detection scheme. This compact and robust instrument has a response time of 0.15 s and can reliably detect short‐term absolute humidity changes as small as 0.6 mg/L (which equate to 0.02% absorption); the long‐term stability of the absolute humidity measurement over a period of 4 days is approximately 1 mg/L. These performance characteristics are particularly well suited to measurements associated with human respiration, and we present results in this humidity regime. ©1995 American Institute of Physics.