A lighting apparatus for use with a battery pack of different rated voltages, the lighting apparatus comprising: a light source; a constant voltage circuit that is configured to adjust an output voltage based on an input voltage from the battery pack so that a constant output voltage is supplied to the light source; and a voltage measurement unit (22, 23) that is configured to measure the input voltage from the battery pack, wherein the constant voltage circuit includes a luminance modulation unit that is configured to: adjust the output voltage so that a constant output voltage is supplied to the light source until the measured input voltage decreases to a dimming initiation voltage; adjust the output voltage to start dimming the light source when the measured input voltage decreases to the dimming initiation voltage or lower; and deactivate the light source when the measured input voltage decreases to lower than or equal to a deactivation voltage, which is lower than the dimming initiation voltage, characterised in that a plurality of thresholds are provided between the dimming initiation voltage and the deactivation voltage, and wherein when the measured input voltage decreases to the dimming initiation voltage or lower, the luminance modulation unit is configured to dim the light source in a stepped manner in accordance with a comparison of the plurality of thresholds and the measured input voltage as the measured input voltage decreases. a light source; a constant voltage circuit that is configured to adjust an output voltage based on an input voltage from the battery pack so that a constant output voltage is supplied to the light source; and a voltage measurement unit (22, 23) that is configured to measure the input voltage from the battery pack, wherein the constant voltage circuit includes a luminance modulation unit that is configured to: adjust the output voltage so that a constant output voltage is supplied to the light source until the measured input voltage decreases to a dimming initiation voltage; adjust the output voltage to start dimming the light source when the measured input voltage decreases to the dimming initiation voltage or lower; and deactivate the light source when the measured input voltage decreases to lower than or equal to a deactivation voltage, which is lower than the dimming initiation voltage, characterised in that a plurality of thresholds are provided between the dimming initiation voltage and the deactivation voltage, and wherein when the measured input voltage decreases to the dimming initiation voltage or lower, the luminance modulation unit is configured to dim the light source in a stepped manner in accordance with a comparison of the plurality of thresholds and the measured input voltage as the measured input voltage decreases. adjust the output voltage so that a constant output voltage is supplied to the light source until the measured input voltage decreases to a dimming initiation voltage; adjust the output voltage to start dimming the light source when the measured input voltage decreases to the dimming initiation voltage or lower; and deactivate the light source when the measured input voltage decreases to lower than or equal to a deactivation voltage, which is lower than the dimming initiation voltage, characterised in that a plurality of thresholds are provided between the dimming initiation voltage and the deactivation voltage, and wherein when the measured input voltage decreases to the dimming initiation voltage or lower, the luminance modulation unit is configured to dim the light source in a stepped manner in accordance with a comparison of the plurality of thresholds and the measured input voltage as the measured input voltage decreases.