R12 bulb is a type of reflector bulb that has a diameter of 12 eighths of an inch, or 1.5 inches. The "R" stands for "reflector," meaning it has a built-in reflector that helps direct light in a focused beam, which makes it useful for specific applications where directional light is required. R12 bulbs are commonly used in applications like elevator lighting, accent lighting, task lighting, or in some appliances.

These bulbs are often found with lower wattage options and are typically used in residential settings, including under-cabinet lighting, track lighting, or even inside some specialty fixtures. The R12 bulb base can vary, so it’s important to match the base type and wattage specifications to your fixture requirements.