(2) Visual elements shall be at least 2½ in (64 mm) in the smallest dimension.
(3) Signals shall be visible from the vicinity of the hall call button (sec Fig. 20). In-car lanterns located in cars, visible from the vicinity of hall call buttons, and conforming to the above requirements, shall be acceptable.
(“ Standards for Accessible Design”, 28 CFR 36 Appendix D)


