Tejal:
Window sill does give it some light and it growing vertical to reach that light , which probably mostly from top and not scatttered.

Most important thing is, that window sill become very cold during winter.Air near windows becomes cold when it comes in contact with glass. I have confirmed it by placing thermometer. Please try to keep plant about a foot away from window. I actually had to remove my tropical plants further away and set up a "Plant growing light". Iturn it on for 3-4 hours a day. Thay are doing much better.

Regards,
Arvind