Systems and methods disclosed herein provide for detecting gas by: illuminating, with a controllable illuminator system, a scene with light including radiation within the infrared (IR) wavelength range; controlling the illuminator system to emit light at a first wavelength corresponding to a first absorption level of a gas and at a second wavelength corresponding to a second absorption level of a gas, such that an equal amount of radiant energy over a time period is emitted onto the scene for each of said first and second wavelengths; and capturing a first IR image of the scene being illuminated with light at said first wavelength and a second IR image of the scene illuminated with light at said second wavelength, and comparing said first and second IR images to determine whether a characteristic for at least one specific gas is represented in said first and/or second IR images.