The brightness of light is typically associated with the intensity or power of the light, which is related to the number of photons emitted or the energy carried by the photons.
The frequency of light, on the other hand, determines its color or wavelength. Light with higher frequencies (shorter wavelengths) tends to appear bluer or more energetic, while light with lower frequencies (longer wavelengths) appears redder or less energetic.
While the number of photons influences the intensity of light, the frequency of photons determines the color or wavelength. So, brightness is primarily related to the number of photons, while color or perceived energy is determined by the frequency of photons.