This answer assumes that seals for the switch and light fixture are the only items of interest and any required boundary seals have already been addressed appropriately.
The first thing to consider is whether the light fixture and switch are factory sealed or not. The nameplates should indicate this.
The odds are very high that any Class I, Division 1 light fixture is factory sealed. If it is, then no field installed seal is required unless the conduit entry is 2? or greater.
If the switch is factory sealed, then again no field installed seals are required unless the conduit entries are 2? or greater. If the switches are not factory sealed then ALL conduit entries must be field sealed within 18? of the switch.