Et lys on the table is a candle, and to lys are two candles; lys as an amount, meget lys, ikke meget lys, is light. Lyset can be either, and the situation usually decides: slukke lyset på badeværelset is turning off the light.
On the sofa en pude is usually a cushion; on the bed it is a pillow. In the same way et tæppe on the floor is a rug, and one you sleep under is a blanket.