Mich. Comp. Laws § 125.465

Sec. 65. Public halls, lighting at night. In every multiple dwelling all public halls shall be kept adequately lighted at all times by the owner. In every multiple dwelling of class "b", except those of fireproof construction having more than 15 rooms or sleeping accommodations for more than 30 persons, the location of stairways and means of egress shall be designated on each floor by electrically illuminated exit signs having letters at least 4 inches in height. All exit lights shall be on a separate circuit or circuits and wires shall be installed in approved metal raceway.