Is ( R )-lactic acid dextrorotatory or levorotatory?
We cannot make an interpretation about optically activeness by looking R configuration or S configuration.
For example one of compoud have R configuration can be levorotory or dextrorotary we cannot make decision about polarized light. It is also true for S configuration.
If you want to know which direction or amount of spesific rotation in polarized light, you must put your sample to polarimeter.