Light does have a constant speed in a vacuum, which is approximately 299,792,458 meters per second (or about 186,282 miles per second). According to the theory of special relativity, developed by Albert Einstein, the speed of light in a vacuum is an absolute constant denoted by the symbol "c."
In the framework of special relativity, the concept of acceleration applies to objects with mass. For objects with mass, such as cars or planets, their speed can change with time, and they can undergo acceleration or deceleration.
However, light consists of massless particles called photons. Photons are not subject to the same rules as massive objects when it comes to acceleration. According to the theory of special relativity, the speed of light in a vacuum is the same for all observers, regardless of their relative motion. It is a fundamental postulate of special relativity that the speed of light is constant and does not depend on the motion of the source or the observer.
This means that light does not need to accelerate to reach its constant speed. From the moment a photon is emitted, it travels at the speed of light without requiring any acceleration or deceleration.
It's important to note that when light interacts with matter, it can be absorbed, reflected, or refracted, which may change its direction or apparent speed within the medium. However, the constant speed of light in a vacuum remains an essential aspect of our understanding of the universe as described by special relativity.