Humans are extremely visual creatures, our reliance on eyesight is one of the defining characteristics of the human experience.
When you turn on a light, it seems as though the light turns on instantaneously and illuminates the area. Though seemingly instant, light actually takes a little bit of time to emit from the bulb to our eyes. This speed is called the Speed of Light. The speed of light is a calculated number that pertains to the time it takes for light to be emitted from a source (like the Sun or a light bulb) and reach our eyes. In a vacuum, the speed of light is exactly 299,792,458 meters per second, or approximately 186,282 miles per second.