Only if you want them to glow and look their best. Galleries know this. You should too.
Proper spotlighting not only emphasizes key areas of the composition, but creates pools of light and dark which enliven the surface of the painting and makes it more visually rich.
As well, a bright spotlight on a specific spot will pull the viewer’s eye to where you want it to go first.
Lighting also heightens the intensity of colours and the variation of textures in any painting.
Ideally, spotlights should be placed on the ceiling in front of the painting. If possible, use a minimum of two spotlights, each coming in from the outer ends and directed toward the centre onto the painting each at 45 degree angles.
Use halogen light bulbs and fixtures as they give a very clean, intense, white light.
Avoid using coloured light bulbs, unless you’re trying to create a specific dramatic effect. Coloured light bulbs will completely distort the colours of any painting.
This is the traditional way of lighting a painting for maximum impact.