At the summer cottage for those who have a house and detached buildings: a barn, a utility unit, a toilet, a bathhouse, a basement, an attic - lighting was provided. At any time, it may happen that one or two light bulbs burn unnecessarily.
To get rid of excess energy consumption, I install all the switches in the corridor of the country house and near each switch I place a light indicator from a flashlight with a voltage of 2.5 V; 3.5 V 6.3 V or 13.5 V. This lamp is connected in series with the switch, that is, in the gap of one of the wires going to the switch. The lamp can be mounted in the switch if its case is transparent, or placed in a transparent box and fixed above the switch. The voltage of the bulb does not matter. The main attention should be paid to the amperage of the bulb from the flashlight: it should be no less than the one that consumes the bulb in the corridor. Data is indicated on the lamp base of the lamp (for example, 6.3 W - 0.22 A; 3.5 W - 0.3 A; 2.5 W -0.15 A). And in order to find out the current strength of the light bulb in the utility room, it is necessary to divide its power by the mains voltage. So, a bulb with a power of 25 W consumes a current of 0.11 A; 40 W -0.18 A, etc.
Knowing which lamp is installed in the utility room, you can pick up the indicator lamp, the current strength of which is close to the current in the utility room and connect it in series to the switch. Selection options: 40 W, 0.18 A - 6.3 W, 0.22 A; 60 W, 0.27 A - 3.5 W, 0.3 A. Such a light indicator will always remind you of a useless light bulb burning.