The High/Low/Off switch on my desk lamp allows this 50W or less halogen bulb to be used. This is a very useful feature. Halogen bulbs come in a variety of names that have different sized plugs/pins on the bulb. The two lamps in this pack are referred to as the T4 JC. If T4 JC is not printed or stamped anywhere on your lamp, lampshade, the original packaging or the documentation that came with your lamp, then this lamp will not fit your lamp sockets correctly. If the numbers do not match, useβ¦