According to the Heisenberg uncertainty principle (HUP), there is a fundamental limit to the precision with which certain pairs of physical properties, such as position and momentum, can be simultaneously known. The HUP states that the more precisely you try to measure the position of a particle, the less precisely you can know its momentum, and vice versa.
In the case of a photon, which is a massless particle, it always travels at the speed of light in a vacuum. This means that its momentum is directly related to its frequency or wavelength, as given by the equation E = hf, where E is the energy of the photon, h is Planck's constant, and f is the frequency. Since the speed of light is constant, the momentum and frequency of a photon are inversely proportional.
Now, if we try to precisely measure the position of a photon, we would need to confine it in a very small region of space. However, confining the photon to a small region would increase the uncertainty in its momentum, due to the inverse relationship mentioned earlier. Consequently, the uncertainty in the momentum of the photon would lead to a larger uncertainty in its wavelength or frequency.
In other words, while the speed of light is always known, attempting to precisely measure the position of a photon will introduce uncertainty in its momentum, and hence in its frequency or wavelength. Therefore, the HUP still applies to photons, making it impossible to simultaneously know both the position and momentum of a photon with arbitrary precision.