Is it safer to smoke light cigarettes during pregnancy?

No. Smoking cessation is very important during pregnant. All smokers should make every effort to stop smoking completely during pregnancy.
No. "light" cigarettes are the product of marketing managers who appeal to your concern about smoking while wishing to maintain their revenue stream. The taste may be "light" and the nicotine content of the smoke may be lower (as advertised), but the large number of poisonous elements in the smoke are still there and you incur significant risk in permitting them to reach your baby.