▁to ▁the ▁identical ▁appearance ▁of ▁the ▁l amps . ▁ ▁The ▁U . S . ▁Supreme ▁Court ▁granted ▁cert ior ari ▁to ▁consider ▁whether ▁this ▁use ▁of ▁a ▁state ' s ▁unf air ▁competition ▁law ▁was ▁compatible ▁with ▁U . S . ▁pat ent ▁law . ▁ ▁R uling ▁of ▁Supreme ▁Court ▁ ▁Justice ▁Black , ▁in ▁the ▁Court ' s ▁opinion , ▁review ed ▁the ▁history ▁of ▁the ▁pat ent ▁mon opol y ▁in ▁English ▁and ▁U . S . ▁law , ▁and ▁wrote ▁that ▁when ▁a ▁pat ent ▁exp ires , ▁or ▁when ▁an ▁item ▁is ▁un pat ent able , ▁then ▁the ▁item ▁" is ▁in ▁the ▁public ▁domain ▁and ▁may ▁be ▁made ▁and ▁sold ▁by ▁who ever ▁cho oses ▁to ▁do ▁so ." . ▁The ▁lower ▁courts ▁had ▁er red ▁by ▁using ▁Illinois ▁unf air ▁competition ▁law ▁to ▁effectively ▁give ▁St iff el ▁Co . ▁a ▁pat ent ▁mon opol y ▁on ▁its ▁un pat ented ▁lamp . ▁ ▁The ▁Court ▁continued ▁that ▁" m ere ▁in ability ▁of ▁the ▁public ▁to ▁tell ▁two ▁identical ▁articles ▁apart ▁is ▁not ▁enough ▁to ▁support ▁an ▁inj unction ▁against ▁copying ▁or ▁an ▁award ▁of ▁dam ages ▁for ▁copying ▁that ▁which ▁the ▁federal ▁pat ent ▁laws ▁permit ▁to ▁be ▁copied ," ▁though ▁it ▁noted ▁that ▁a ▁state ▁could ▁require ▁that ▁goods ▁be ▁l abeled ▁in ▁order ▁to ▁prevent ▁consum ers ▁from ▁being ▁mis led ▁as ▁to ▁the ▁source ▁of ▁an ▁article ; ▁but ▁that ▁this ▁was ▁a ▁trade ▁dress ▁issue , ▁and ▁that