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In most campers, MOST, but not all lighting is 12VDC, supplied by the battery or converter if plugged into 120 VAC "Shore Power". Of the 35+ lights in my camper, the table lamp by the recliner and the ceiling fan light are the ONLY 120 v lights. Many styles of 12V lights are available on line in LED, halogen, florescent and incandescent varieties. These will work without being plugged into shore power.
120V is used for heavy power users like A/C, microwave, fridge and water heater. It is also for our luxuries like TV and DVD.
You can use the 120V lights from the local big box store, but you will likely need to do some wiring to supply them with 120V and you are restricted to being plugged in for them to work.