The speed of light is the same for all wavelengths in vacuum. According to Einstein's theory of relativity, the speed of light in vacuum is a constant value of 299,792,458 meters per second (or about 3 x 10^8 m/s). Therefore, the speeds of light with wavelengths of 4000 angstrom and 8000 angstrom are the same in vacuum and equal to 299,792,458 meters per second.
