The A3L4AA-6L5R is an Allen-Bradley A3 series pilot light: a 120V transformer-type red LED indicator, panel-mount with a full-voltage transformer for the LED circuit. The transformer steps line voltage down to drive the LED, giving consistent brightness across the rated range and isolating the lamp from line transients. It's the kind of part you find on MCC bucket doors, control station enclosures, and operator panels where a red run/stop or fault indication is needed.
The 120 VAC transformer input means this pilot light connects directly to a 120 V control circuit — no dropping resistor or separate LED power supply needed. The transformer inside provides isolation, which matters in panels where a shorted LED could otherwise backfeed line voltage onto a PLC output card. The red LED gives a clear visual state; if your panel uses green for run and red for fault, this is the fault-side indicator.