The beautiful bones of a cathedral-height exposed beam ceiling deserve special treatment when it comes to lighting. After all, one of the benefits of exposed beams is the dramatic look the beams present, so giving time and effort to equally dramatic lighting makes sense. There are several ways both to light the beams themselves and to install lighting in the beams so as to provide lighting for the room in general.
Although it is possible to "up-light" exposed beams with a general wash of light from below, providing too much general wash will only illuminate the beams and cross beams in an even and rather bland manner. A much more dramatic treatment is to light the overhead beams intentionally unevenly, producing bold shadows and contrasts. Dramatic lighting is, after all, a game of producing strong contrasts between light and dark, hot and cold. The only time a general wash is desirable for an outstanding ceiling is when the ceiling has been painted or decorated with stencils or mosaics.
You can achieve this bold contrast by installing spotlights around the perimeter of the room at the highest point of the side walls and shooting spots up and across the beams at an angle. Provide brighter highlight or "key" lighting with spotlight lamps of a higher wattage than weaker "fill" lamps that are perhaps half the wattage of the "key" lamps. For example, use 100-watt halogen lamps for "key" spots and 50-watt lamps for the "fills." Make sure the "key" lights are placed on one side of the room and that "fill" lights are situated on the opposite wall to get the most out of this "key-and-fill" contrast scheme. Install such up-light spots in covered cans or spotlight fixtures to shield guests from harmful glare.
Spots Mounted on Beams
If mounting spotlight cans on the walls isn't possible, or if the spotlight cans produce an unattractive result, you can mount adjustable-focus cans on the beams themselves, positioning them at the far edges, where the beams meet the walls. Because these spotlights must be mounted so close to the beams, they can only be focused to deliver glancing shafts of light across the beams. Glancing lights produce a much different look than full up-lights but can be just as dramatic in terms of the shadows produced. "Key-and-fill" techniques can work in this situation just as well. Make every effort to avoid shining these bright lights in the eyes of guests below, however.
If your beamed ceiling is not architecturally spectacular or lacks larger beams for casting deeper contrast shadows, give it some dramatic punch nonetheless by arranging shadow-casting objects such as urns filled with sticks or silk plant fronds in front of up-light cans. Make sure the objects do not make contact with any hot spotlights. The shadows cast by these objects across the ceiling will give the beams more depth and character.
Recessed Lights Between Beams
You can install recessed cans or pot lights in the ceiling between beams to produce nice lighting for the room below without seriously marring the look of the beams. Avoid placing pot lights so close to beams that "flares" or "hot spots" are produced on the beams when the pot lights are illuminated.