The PAR 30 bulb is 3.75 inches and suitable for indoor track and ceiling lighting as well as outdoor floor and display lighting. They offer high-quality brilliance that brings out textures in clothing and linens, like in a retail store display or in theatrical productions. Position these bulbs outside for security purposes, or to light up holiday house decorations. They can be used to light up lobbies in office buildings or outdoor areas at bars and restaurants as well. The options are virtually endless with these high-quality, energy efficient and long lasting light bulbs.