Selecting Harp Lampshades
Most lamps have harps requiring shades with washer fitters. This shade type is built on a wire frame with a three wire spider and centered ring washer near the top of the shade. The washer ring slips down onto a harp, 1/8 IP pipe or cluster stem and is held in place with a lamp finial.
A few parameters make replacing table lamp shades easier. That being said there are generalizations, no hard and fast rules. It is always best to let your personal taste be the guiding influence.
Achieving a sense of balance and harmony between table lampshade and lamp base will present the best appearance. Lamp shade proportions should reflect lamp base proportions.
Most table lamps are tall and slender. For these lamps the height of the lamp base will determine the bottom diameter of the new lamp shade.
Measure the lamp base height: distance between base (at table surface) to bottom of socket.
Select shade with a bottom measurement within 1" - 2" of lamp base height
Height of shade should be proportional to base. A good starting point is to try a shade approximately 2/3rd's the height of lamp base.
Some lamps have short squat bases requiring differently proportioned table lamp shades.
Measure the diameter of the lamp base at it's widest point.
Select shade with a base diameter 1-1/4 to 1-1/2 times larger than the widest portion of base.
Height should be similar to height of lamp base. Proportion is always a guiding factor. Shades for this style lamp tend to be shorter than shades used on taller lamps.
Replacing a Table Lamp Shade on any lamp:
The bottom edge of the lamp shade should cover the socket but not the lamp base.
Determining the correct lamp shade position is best accomplished by viewing the lamp on the surface on which it will be permanently placed. Perspective changes when a lamp is place high on a mantel verses lower on a table.
Although a table lamp shade is used on lamp pipe and cluster stems the vast majority are used with a harp.
The advantage of harps is the ability to readily switch to different heights providing easy vertical adjustment. Harps are 2 part: U-shape bottom bracket with a detachable top harp. Typically harp and shade heights are the same or similar.