noun
signal light; indicator light
General term for any light used to convey a signal, such as on a control panel, vehicle dashboard, or traffic signal.
機械の信号灯が赤く点滅している。
The machine's signal light is flashing red.
noun
Specifically refers to a mechanical or optical signaling device using moving arms or lights, often in railway or maritime contexts.
昔の鉄道では信号灯として腕木式信号機が使われていた。
On old railways, semaphore signals were used as signal lights.
交通信号 is a traffic signal (often the whole system), whereas 信号灯 can refer to a single signal light unit.
Compound of 信号 (signal) + 灯 (light).