Why is the oil light on after changing the oil.

Used High millage 10W30, changed the oil,air,gas filter as well as the pcv valve and the oil light comes on, but when I accelerate the light goes out and of course come back when idle. The auto, part store suggested that the 10W30 oil was probably too light and I should add some Lucas additive for viscosity, that was done still the problem persists.

Please help.