noun
red light; stop light; danger signal
Refers to a red warning lamp, such as a traffic stop light, a railway signal, or an indicator on a device.
赤ランプが点灯したら、すぐに機械を止めてください。
If the red light comes on, please stop the machine immediately.
踏切の赤ランプが点滅しているときは渡ってはいけません。
Do not cross when the red light at the railroad crossing is flashing.