A luminous unit for an optical gas detector, an optical gas detector including the luminous unit, and a method of recording an absorption spectrum in an optical gas detector include a light source for linearly polarised light radiation and a housing with an exit window. A wavelength of the light radiation radiated from the light source is tunable. The light source is arranged in the housing such that the main emission direction (OA) of the light source encloses an inclination angle (φ) of between 10° and 50° with a normal (N) to the main extension plane (HE) of the exit window. The direction of polarisation (P) of the light radiation encloses a rotation angle (θ) of between 22.5° and 67.5° with the plane of incidence on the exit window.