What is the difference between an RX switch and an RX-LC (low current) switch?

The standard Von Duprin switches (RX and LX switches in exit devices, and DS dual switches in 6100 and 6200 Electric Strikes) are rated for 0.05A to 2A @ 24 VDC.

The low current (LC) switches are rated for current up to 0.05A @ 24 VDC.

Note that the switches do not use power themselves. The switches are connected to something (for example, a security system) that is monitoring the condition of the switch, and that monitoring item determines the Amps it is routing through the switch.  Therefore, the monitoring item determines which switch would be appropriate for the application.

As a switch changes state, the closed circuit changes between the Normally Open and Normally Closed terminals of the switch; and if there is enough amperage going through the switch, then the electrical current will cause an electrical arc just before they touch.  This arc cleans minute amounts of corrosion that might have built up on the terminal (imagine a car battery or old remote control battery, but not as extreme).

The Low Current switches are used when the current (A) is not high enough to create that arc, so the terminals are made of a different material to resist the buildup of corrosion on the terminals of the switch.

If the regular switch is used in a low current application, eventually the corrosion will build up enough to cause the switch to fail.

If a Low Current switch is used in a higher current application, the higher current will eventually burn up the terminals of the LC switch, also causing the switch to fail.