According to the theory of special relativity, as formulated by Albert Einstein, massless particles such as photons (which light is composed of) always travel at the speed of light in a vacuum. This means that from the perspective of a photon, time does not pass, and its journey is instantaneous.
However, it is important to note that we cannot directly observe or experience what it is like to move at the speed of light. From our perspective as observers, we perceive light as having both frequency and wavelength.
The frequency of light refers to the number of wave crests that pass a given point per unit of time. The wavelength of light is the distance between two successive wave crests. These two properties, frequency and wavelength, are related through the equation: speed of light = frequency × wavelength.
When light moves at the speed of light, it still possesses a frequency and wavelength as observed by other observers. However, the relationship between frequency and wavelength changes due to the relativistic effects of time dilation and length contraction. This means that different observers may measure different values for the frequency and wavelength of light, depending on their relative motion.
In terms of visibility, light does not become invisible to us if it moves at the speed of light. Our ability to perceive light depends on its interaction with our eyes or detectors, which is determined by its frequency or wavelength. Different frequencies of light correspond to different colors in the visible spectrum. So, even though the properties of light may change for observers in relative motion, it remains a fundamental part of our perception and understanding of the world around us.