Signal Lamp Guide: Choosing the Right Panel Indicator Light

On a control panel, a signal lamp is the indicator light that tells an operator what a machine is doing at a single glance. It is the lit dot beside the switches, not the tower beacon on top of the machine. Get the colour, the lamp technology or the voltage wrong, and a status light that should reduce confusion starts creating it. This guide covers what a signal lamp is, why its colour is not a free choice, why LED has replaced older lamps, and how it wires into the panel alongside a pushbutton.

What Is a Signal Lamp?

A signal lamp is a panel-mounted indicator light that shows the operating status of a machine or circuit: power on, running, ready or fault.

The standard format is a 22mm panel cutout with single-hole mounting, a coloured lens on the front and an LED or lamp element behind it. That is the same footprint as the pushbuttons it sits next to, which is why lamps and switches share a panel line and one mounting standard. What a signal lamp is not is a beacon or stack light. Those are separate signalling devices mounted on top of a machine for across-the-room visibility. 

Signal Lamp Colours Are Not a Free Choice

Indicator colours follow a convention. IEC 60073 sets the meaning of colours for indication, and IEC 60204-1 applies it to machinery, so a colour carries the same message on every compliant panel. Choosing a colour at random throws that away.

The rule most people get wrong is red. On an indicator, red means fault or danger, so it should never be used for "power on." A power-on lamp is white or green. Wire the mains-on light in red and you slowly train operators to treat red as background noise, which is the last thing you want the day a real fault lights up.

This convention is even stricter on the actuator side, which is why an emergency stop button is always red on a yellow background. The indicator and the control speak the same colour language, and keeping them consistent is what makes a panel readable under pressure.

LED vs Filament Signal Lamps

Modern signal lamps are almost all LED, and for panel work the reasons are concrete rather than marketing.

The maintenance argument is the one that lands on a real line. A filament lamp running two shifts burns out often enough to become a standing task, and every replacement means opening a live cabinet. An LED signal lamp effectively outlives the panel around it. One caution: match the rated voltage exactly, because unlike a filament bulb an LED element does not tolerate the wrong supply.

How a Signal Lamp Wires Into the Panel

A signal lamp is driven by the control circuit, not wired inline with the load it reports on. On a Singapore panel the voltage is usually 24V DC for anything PLC-driven, or 230V AC for direct mains indication, so confirm which before ordering, because the lamp element is voltage-specific.

The connection to a pushbutton is where the switch cluster meets the indicator. An illuminated pushbutton combines a switch and a signal lamp in one 22mm unit, with a lamp element behind the actuator and a separate contact block doing the switching. Use a standalone signal lamp when the indication is independent of operator action, and an illuminated pushbutton when the light confirms the button's own function. If you are specifying the switches themselves, our guide on momentary versus latching pushbuttons covers the actuator side.

Choosing a Signal Lamp for Singapore Panels

IP rating comes first. A signal lamp on an exposed panel front in a workshop or wet process area needs a front-of-panel seal of IP65 or better, the same as the switches beside it, because a lamp is a hole cut in the panel and a weak seal quietly undoes the enclosure's rating. Humidity and heat point the same way: continuous operation in an un-air-conditioned workshop favours LED, which runs cool where filament life would suffer. Keep the 22mm range consistent across LED indicators, lamps and pushbuttons so the whole front uses one standard.

FAQs About Signal Lamps and Panel Indicators

What is the difference between a signal lamp and a beacon?

A signal lamp is a small panel-mounted indicator read at arm's length. A beacon or stack light is a larger device mounted on top of a machine for visibility across a room.

What colour should a "power on" indicator be?

White or green. Red is reserved for fault and danger, so using it for power on weakens its meaning.

Are signal lamps always LED now?

Almost always. LED lasts far longer, runs cooler and resists vibration, so filament indicators are mostly limited to legacy replacements.

What is an illuminated pushbutton?

A single 22mm unit combining a switch and a signal lamp, so one button both issues a command and shows its own status.

What voltage do panel signal lamps use?

Commonly 24V DC on PLC-driven panels, or 230V AC for direct mains indication. The lamp element is voltage-specific, so it must be ordered to match.

Match the Signal Lamp to the Status It Shows

The rule in one line: pick the signal lamp colour to the convention, choose LED for life and reliability, match the voltage, and use an illuminated pushbutton where the light confirms the button.

Sisco Interconnect supplies RAFI signal lamps and panel indicators, LED indicators and illuminated pushbuttons in the 22mm range, stocked in Singapore for control and automation panels. Send us your panel layout and control voltage and we will match the indicators to your switches. Contact our team.