A gas detector for monitoring a target gas, the gas detector comprising: a gas inlet; an ultraviolet lamp; a pair of electrically biased electrodes (414a, 414b) provided between the gas inlet and the UV lamp; a switch operable to switch the UV lamp between a first mode and a second mode; and a processor, the processor being configured to communicate with the pair of electrically biased electrodes, wherein the processor is configured to operate the switch, wherein the processor is further configured to control the gas inlet; and characterized in that the processor is further configured to perform the following: operating the UV lamp in a second mode, the second mode being a non-operating mode thereof, so that photons are not emitted from the UV lamp, and determining an absolute zero level, the absolute zero level representing electric noise; operating the UV lamp in a first mode and preventing the target gas from entering the gas inlet, the first mode of the UV lamp being an operating mode of the UV lamp, so that UV light is emitted therefrom, and determining a photoelectric noise level of the UV light emitted from the lamp, when the pair of electrically biased electrodes are exposed to the UV lamp in the first mode and are prevented from being exposed to the target gas, the determined photoelectric noise level being a difference between an electrode signal generated by the pair of electrically biased electrodes and the determined absolute zero level; executing real time update of the absolute zero level; and opening the gas inlet to the target gas, operating the UV lamp in the first mode and computing a calibrated output reading, the calibrated output reading, when the pair of electrically biased electrodes are exposed to the UV lamp in the first mode and are exposed to the target gas, being the electrode signal generated by the pair of electrically biased electrodes minus the photoelectric noise level and the updated absolute zero level. a gas inlet; an ultraviolet lamp; a pair of electrically biased electrodes (414a, 414b) provided between the gas inlet and the UV lamp; a switch operable to switch the UV lamp between a first mode and a second mode; and a processor, the processor being configured to communicate with the pair of electrically biased electrodes, wherein the processor is configured to operate the switch, wherein the processor is further configured to control the gas inlet; and characterized in that the processor is further configured to perform the following: operating the UV lamp in a second mode, the second mode being a non-operating mode thereof, so that photons are not emitted from the UV lamp, and determining an absolute zero level, the absolute zero level representing electric noise; operating the UV lamp in a first mode and preventing the target gas from entering the gas inlet, the first mode of the UV lamp being an operating mode of the UV lamp, so that UV light is emitted therefrom, and determining a photoelectric noise level of the UV light emitted from the lamp, when the pair of electrically biased electrodes are exposed to the UV lamp in the first mode and are prevented from being exposed to the target gas, the determined photoelectric noise level being a difference between an electrode signal generated by the pair of electrically biased electrodes and the determined absolute zero level; executing real time update of the absolute zero level; and opening the gas inlet to the target gas, operating the UV lamp in the first mode and computing a calibrated output reading, the calibrated output reading, when the pair of electrically biased electrodes are exposed to the UV lamp in the first mode and are exposed to the target gas, being the electrode signal generated by the pair of electrically biased electrodes minus the photoelectric noise level and the updated absolute zero level. operating the UV lamp in a second mode, the second mode being a non-operating mode thereof, so that photons are not emitted from the UV lamp, and determining an absolute zero level, the absolute zero level representing electric noise; operating the UV lamp in a first mode and preventing the target gas from entering the gas inlet, the first mode of the UV lamp being an operating mode of the UV lamp, so that UV light is emitted therefrom, and determining a photoelectric noise level of the UV light emitted from the lamp, when the pair of electrically biased electrodes are exposed to the UV lamp in the first mode and are prevented from being exposed to the target gas, the determined photoelectric noise level being a difference between an electrode signal generated by the pair of electrically biased electrodes and the determined absolute zero level; executing real time update of the absolute zero level; and opening the gas inlet to the target gas, operating the UV lamp in the first mode and computing a calibrated output reading, the calibrated output reading, when the pair of electrically biased electrodes are exposed to the UV lamp in the first mode and are exposed to the target gas, being the electrode signal generated by the pair of electrically biased electrodes minus the photoelectric noise level and the updated absolute zero level.