94 Mercury Villager oil pressure light flickers; stays on

The other day when I started the van, the oil pressure light flickered and then stayed on. I immediately turned off the engine and waited for about 15 minutes for everything to settle. I checked the oil level and it was low and I put about a 1/4 quart of Synthetic 5W-30 oil in so not to overfill. I drove home 70 miles and the light did not come back on. What are the possible causes?

I would check the oil sending sensor located on the oil filter housing.