A method of maintaining a ventilation treatment device positioned downstream of an exhaust hood, comprising: detecting an intensity of at least one ultraviolet light source continually by a sensor; at successive points in time during operation thereof in the ventilation treatment device, polling the sensor with a controller to apply signals representing the intensity to a controller; storing data responsive to the detected intensities in a data store; characterised in that the method further comprises: the controller, at a first time, on a user output terminal, generating an indication that the at least one ultraviolet light source requires cleaning when the detected intensity is below a second threshold; the controller, at a second time subsequent the first time, determining whether a first command has been input by a user through the user output terminal as a first maintenance indication indicating the completion of a cleaning of the at least one ultraviolet light source; the controller, at a third time subsequent the second time, on the user output terminal, generating an indication that the at least one ultraviolet light source requires replacement if the intensity of the at least one ultraviolet light source is not above a first threshold after the cleaning, the first threshold corresponding to a lower intensity than the second threshold; the controller, at a fourth time subsequent the third time, determining whether a second command has been input by the user through the user output terminal as a second maintenance indication indicating the completion of a replacement of the at least one ultraviolet light source has been received; and the controller preventing operation of the exhaust hood if no maintenance indication is received via an input by the user through the user output terminal within a predefined period of time or a predefined number of startups of the system. detecting an intensity of at least one ultraviolet light source continually by a sensor; at successive points in time during operation thereof in the ventilation treatment device, polling the sensor with a controller to apply signals representing the intensity to a controller; storing data responsive to the detected intensities in a data store; the controller, at a first time, on a user output terminal, generating an indication that the at least one ultraviolet light source requires cleaning when the detected intensity is below a second threshold; the controller, at a second time subsequent the first time, determining whether a first command has been input by a user through the user output terminal as a first maintenance indication indicating the completion of a cleaning of the at least one ultraviolet light source; the controller, at a third time subsequent the second time, on the user output terminal, generating an indication that the at least one ultraviolet light source requires replacement if the intensity of the at least one ultraviolet light source is not above a first threshold after the cleaning, the first threshold corresponding to a lower intensity than the second threshold; the controller, at a fourth time subsequent the third time, determining whether a second command has been input by the user through the user output terminal as a second maintenance indication indicating the completion of a replacement of the at least one ultraviolet light source has been received; and the controller preventing operation of the exhaust hood if no maintenance indication is received via an input by the user through the user output terminal within a predefined period of time or a predefined number of startups of the system.