Most desk lamps have replaced old-fashioned incandescent bulbs with LED fixtures which have a number of advantages over their older counterparts. They last much longer and are more energy-efficient, meaning you likely will never have to replace them. Also, some bulbs can be adjusted for brightness and temperature based on your preferred lighting environment. These bulbs can still be replaced but are often specific to the kind of lamp you're using, so make sure to check your lamp's specifications before ordering a replacement.