out ▁served ▁to ▁sil hou ette ▁Al lied ▁sh ipping ▁and ▁thus ▁expose ▁them ▁to ▁German ▁sub marine ▁attack . ▁Coast al ▁communities ▁resist ed ▁the ▁im position ▁of ▁a ▁black out ▁for ▁amen ity ▁reasons , ▁cit ing ▁potential ▁damage ▁to ▁tour ism . ▁The ▁result ▁was ▁a ▁dis astr ous ▁loss ▁of ▁sh ipping , ▁dub bed ▁by ▁German ▁sub mar in ers ▁as ▁the ▁" Second ▁Happy ▁Time ". ▁Black outs ▁were ▁held ▁in ▁cities , ▁and ▁along ▁the ▁coast al ▁areas ▁long ▁after ▁any ▁enemy ▁threat ▁existed ; ▁the ▁primary ▁purpose ▁was ▁psych ological ▁motiv ation ▁of ▁the ▁civil ian ▁population ▁which ▁saw ▁black outs ▁as ▁a ▁patri otic ▁duty . ▁ ▁Te chni ques ▁ ▁L ights ▁can ▁simply ▁be ▁turned ▁off ▁or ▁light ▁can ▁sometimes ▁be ▁minim ized ▁by ▁t arring ▁the ▁windows ▁of ▁large ▁public ▁structures . ▁In ▁World ▁War ▁II , ▁a ▁dark ▁black out ▁cur tain ▁was ▁used ▁to ▁keep ▁the ▁light ▁inside . ▁T arring ▁the ▁windows ▁can ▁mean ▁a ▁semi - per man ent ▁black out ▁status . ▁ ▁During ▁the ▁ 1 9 4 0 s ▁and ▁ 1 9 5 0 s , ▁cities ▁such ▁as ▁Detroit ▁would ▁pract ise ▁black out ▁air ▁ra id ▁dr ills . ▁During ▁this ▁time , ▁the ▁city ' s ▁Civil ▁Def ense ▁workers ▁would ▁immediately ▁activ ate ▁the ▁neighborhood ▁air ▁ra id ▁sir en ▁and ▁families ▁would ▁be ▁required ▁to ▁do ▁the ▁following ▁in ▁order : ▁▁ ▁Sh ut ▁off ▁all ▁app li