That's the requirement for the license plate lamp. I think the original poster is talking about the tail/brake lamp.
Bad idea. And illegal. Note that the "... of the prescribed type and meet the prescribed standards" applies to original-equipment lamps. In other words, if the vehicle came from the original manufacturer with original-equipment lamps that are "tinted" or "covered", but the lamps are certified to meet the applicable standards
taking into account the tinting that is already on them from original equipment then that's legal, but after-the-fact modifications of this nature are not (and are really, really dumb). This is why certain VW GTI cars had tinted taillamps as original equipment - they were DOT-approved that way, with the tint already in place.
Attachment that affects lamps prohibited
(7) No person shall drive upon a highway a motor vehicle if either or both of the lamps that are required on the front of the vehicle by subsections (1), (2) and (3),
(a) are coated or covered with a coloured material; or
(b) have been modified by the attachment to the lamps or the motor vehicle of any device that reduces the effective area of the lenses or the intensity of the beam of the lamps. 2002, c. 18, Sched. P, s. 19 (1).
Exception
(7.1) Clause (7) (a) does not apply if the lamps are of the prescribed type or meet the prescribed standards. 2002, c. 18, Sched. P, s. 19 (1).
Edit: FAIL. The above section applies to lights on the FRONT of the vehicle. Hang on; there's something else about tail lamps.