Determining the max current through a coil
The 12 V/100 mA rating means that the coil is intended to be operated on 12 volts, and will draw 100 mA at that voltage.
If you really have a high-power LED rated for 250 mA, you can connect it as shown. The value of Rc should be chosen to drop about 5.5 volts at 100 mA.