An NDIR gas-sensor arrangement for measuring a target-gas concentration comprises a variable-power infrared-radiation emitter that can project radiant energy from one side of a space containing the target gas and through the space to the other side thereof, a infrared-radiation receiver on the other side of the space and positioned to be irradiated by the radiant energy projected by the emitter through the space for emitting a signal corresponding to radiation received, and a filter between the receiver and the space and permeable only to radiation of a wavelength range that corresponds to the target gas. A controller connected to the radiation receiver calculates the target-gas concentration on the basis of the signal from the receiver to the controller.