A luminous intensity measuring device includes a photoresistor, a number of voltage-dividing resistors, a plurality of comparators, a micro control unit (MCU), and an indicator. The photoresistor is connected to a current-limiting resistor in series between a direct current (DC) power supply and ground. The voltage-dividing resistors are connected in series, and together are connected parallel to the photoresistor and the current-limiting resistor located between the DC power supply and ground. A non-inverting node between the photoresistor and the current-limiting resistor is connected to the non-inverting input terminals of the comparators. The inverting terminals of the comparators are respectively connected to inverting nodes between every two adjacent voltage-dividing resistors. The output terminals of the comparators are connected to the input terminals of the MCU. The indicator is connected to the output terminals of the MCU. The MCU controls the indicator to indicate luminous intensity.