Perhaps you should try some spelling variations:
thong cong » trong cong, tong cong, thong thong
hieu lang » chieu sang, hieu quang, nhieu tang
hanh dinh » thanh dinh, hinh dinh, hanh tinh
dang cong » dung cong
quang dau » quang bau, quang dai, quang dam
doi hieu » doi chieu, doc hieu, doi hien
dinh cua » dinh cuu, sinh cua, dinh cu

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: doi hieu lang - hanh dinh cua ((thong cong) OR (dang cong)) tinh quang dau~.
• Adding a wildcard symbol may retrieve word variants: doi hieu lang - hanh dinh cua ((thong cong) or (dang cong)) tinh quang dau*.