According to the LTA (Land Transport Authority) of Singapore rules and guidelines of Tinted Glass.
1) They must be non-reflective. 2) At least 70% of light must be able to pass through the front windscreen and the two front side windows 3) At least 25% of light must be able to pass through the rear windscreen and the two rear side windows. You can visit the onemotoring.com website for more details.