Stack light is also called signal tower light. It is a multi-color warning light. The function is to warn of danger or problems.
Stack light color standards and meaning
Colors standards are red, yellow, green, and sometimes also blue
Red means stop, or warning.
Green means all usually is, the machine is working good
Yellow means idle, or something unusual.
Blue means any function not included in the above colors
Stack light wiring diagram
There is 3 type of wiring connection. It is PNP, NPN, and Contact type.
The PNP and NPN type is connected with power directly. The difference is to see the colorful side is connected with the negative end to the position end. Because it is connected to power directly, so for safety, it is normally used at a voltage of 24V or 12V. You can see the details in the following picture
The special one is the contact type. The colorful end is not connected with power directly for this type. There is a part in the driver to change the voltage to 24V and then connects with the colorful ends. And the other side will be connected to the power. Normally, it is used in some high voltage like 110V, 220V, or 240V. The following picture shows you the details.
The Signal Tower Light application
Normally, it is used in some CNC machine tools, like CNC milling, CNC grinding machines, CNC lathes, etc. But it also can be used in an assembly line or workshop. especially, it can be used in check-out counters of supermarkets.