Answer:
Please see below as the answer is self-explanatory.
Step-by-step explanation:
In order to measure any distance reliably, the best way is using something with a constant, measurable speed, and a definite time interval, so it can be applied the average speed definition:
The laser (light amplification by stimulated emission of radiation) light meets all these requirements, due to its speed in vacuum is well known, and due to its coherence (all the light emitted has the same phase (which means that have the same energy level, at a single frequency), so it is not dispersed, keeping within a very narrow beam through all the trajectory) it can reach to the moon and bounce back without any attenuation, so just measuring the time interval between the emission of the light and the arrival of the returning light, the distance travelled (half of this) can be accurately and reliably measured.
It is not possible do the same with the white light produced by a very powerful searchlight due to the non-coherence of the light emitted, which will be spread out in the space before arriving the moon, as it happens with a light bulb.