A light source and a method for its use in an optical sensor are provided, the light source including a resistively heated element. The light source includes a power circuit configured to provide a pulse width modulated voltage to the resistively heated element, the pulse width modulated voltage including: a duty cycle with a first voltage; and a pulse period including a period with a second voltage, wherein: the duty cycle, the first voltage, and the pulse period are selected so that the resistively heated element is heated to a first temperature; and the first temperature is selected to emit black body radiation in a continuum spectral range. Also provided is an optical sensor for determining a chemical composition including a light source as above.

An infrared light source includes an emitting element extending as a radial plane about the emitting element's center and configured to heat up to emit infrared light. The emitting element lies in a cavity bounded by a cover, placed facing the emitting element. The cover has internal and external faces, the internal face facing the emitting element, and the external face defining an interface between the cover and a medium outside the light source. The cover occupies, parallel to a transverse axis perpendicular to the radial plane, a thickness, between the internal and external faces. The external face includes a planar central portion and at least one peripheral portion adjacent and inclined respective to the central portion. The planar central portion extends about the external face's center. In the peripheral portion, the cover's thickness decreases as a function of a distance from the central portion.

A potential difference between a first terminal and a second terminal of a light emitting element is maintained at a first value or more in a first measurement period, and is maintained at 0V or more and less than the first value in a third measurement period, a concentration of the measurement target gas is measured based on a second intensity of the light received by the light receiving element during a second measurement period which starts at a second timing that is later than a first timing at which the first measurement period starts and before a third timing at which the third measurement period starts and a fourth intensity of the light received by the light receiving element during a fourth measurement period which starts at a fourth timing that is later than the third timing and before a next occurrence of the first timing.