any well-known students or followers of his?
Yes, "Johan de Witt" and "René Descartes".
Isaac Beeckman
He himself was a teacher to Johan de Witt and a teacher and friend of René Descartes. 
what is the value of speed of light in vaccum Its exact value is defined as “approximately”, because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of second. who was the first to attempt to measure it? "Isaac Beeckman", in 1629. who is he? He was a Dutch philosopher and scientist. did he also teach? Yes, he taught at a school in Rotterdam.
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Isaac Beeckman [SEP] Teachers, pupils, and Descartes
Beeckman's most influential teachers in Leiden probably were Snellius and Simon Stevin. He himself was a teacher to Johan de Witt and a teacher and friend of René Descartes. Beeckman had met the young Descartes in November 1618 in Breda, where Beeckman then lived and Descartes was then garrisoned as a soldier. It is said that they met when both were looking at a placard that was set up in the Breda marketplace, detailing a mathematical problem to be solved. Descartes asked Beeckman to translate the problem from Dutch to French. In their following meetings Beeckman interested Descartes in his corpuscularian approach to mechanical theory, and convinced him to devote his studies to a mathematical approach to nature.