"DOT Approved" does not mean street legal. All it means is that it has been tested and is safe for use on your vehicle. There are plenty of aftermarket lighting add ons that are DOT Approved but do not comply with section 108 of the FMVSS. Which is the section that deals with vehicle lighting. Then there are also state and local laws that can be stricter than what the feds have outlined. So basicly a "DOT Approved" stamp means jack by itself.
Here is a link to Section 108 of the FMVSS if you care to read it.
http://www.gpo.gov/fdsys/pkg/CFR-2011-title49-vol6/pdf/CFR-2011-title49-vol6-sec571-108.pdf
Here is a link to Section 108 of the FMVSS if you care to read it.
http://www.gpo.gov/fdsys/pkg/CFR-2011-title49-vol6/pdf/CFR-2011-title49-vol6-sec571-108.pdf