.There is a verse in Rigveda(1,50-4) "Yojananam sahastra dwe dwe shathe dwe cha yojane Aken nimishardhena krammana Namosthuthe" In this verse poet respects to sunlight who moves 2202 yojana in half minute.
When we actually convert yojana to kose and kose to yard and yard to metres.we actually get 299,792,458m/s which is the modern accepted answer. Do the early poets conducted any experiment to measure or the question end up philosophically;because it took about 300 years to calculate speed of light for scientific community.