Is it safe to take vit c capsules for lightening my skin ?

Yes, very safe: Yes, vitamin C is extremely safe and non-toxic. I do not know if there is any research that proves this but many people claim that Vitamin C has helped and there is reason to think it might work via raising glutathione levels. See http://www.whiterskin.info/how-taking-extra-vitamin-c-lightens-skin/ and http://tinyurl.com/pfqahyo for details.

In general: Vitamin C supplementation is safe, but it won't likely do much in regards to skin lightening. You should avoid doses of more than 2000 mg/day unless your doctor instructs such. Also, be aware if you are at risk for kidney stones or have had them in the past, I would review vitamin C use with your doctor.