It is typically used to indicate if assistance is needed, such as when a jackpot has been won or the machine requires maintenance. The color of the candle may vary to show different messages, such as one color for low funds and another for a big win. It helps casino staff easily monitor and address issues with slot machines without needing to inspect each one closely.
Candle Example
For example, if a player hits a jackpot, the candle on the machine will light up to alert casino staff to verify the win.