This is a genuine replacement 40 watt bulb for a microwave. The bulb is meant to light up the underside of the microwave or inside of your microwave when the door is open or during use. If your bulb is not illuminating, you may need to replace it. If the bulb is shattered, be sure to use protective gloves during replacement. Always unplug your microwave before completing any repairs. We suggest ordering a spare, as this is a common wear part.