▁back sc atter ▁direction , ▁the ▁light ▁intensity ▁is ▁subject ▁to ▁numerous ▁essentially ▁random ▁fl uct u ations ▁called ▁spe ck les . ▁ ▁This ▁is ▁one ▁of ▁the ▁most ▁robust ▁inter ference ▁phen omena ▁that ▁surv ives ▁multiple ▁scatter ing , ▁and ▁it ▁is ▁regarded ▁as ▁an ▁aspect ▁of ▁a ▁quantum ▁mechanical ▁phenomen on ▁known ▁as ▁weak ▁local ization ▁( A kk erm ans ▁et ▁al . ▁ 1 9 8 6 ). ▁In ▁weak ▁local ization , ▁inter ference ▁of ▁the ▁direct ▁and ▁reverse ▁paths ▁leads ▁to ▁a ▁net ▁reduction ▁of ▁light ▁transport ▁in ▁the ▁forward ▁direction . ▁This ▁phenomen on ▁is ▁typical ▁of ▁any ▁coh er ent ▁wave ▁which ▁is ▁multiple ▁scattered . ▁It ▁is ▁typically ▁discussed ▁for ▁light ▁waves , ▁for ▁which ▁it ▁is ▁similar ▁to ▁the ▁weak ▁local ization ▁phenomen on ▁for ▁electrons ▁in ▁dis ordered ▁semi - con duct ors ▁and ▁often ▁seen ▁as ▁the ▁prec ursor ▁to ▁Anderson ▁( or ▁strong ) ▁local ization ▁of ▁light . ▁We ak ▁local ization ▁of ▁light ▁can ▁be ▁detected ▁since ▁it ▁is ▁manif ested ▁as ▁an ▁enh ancement ▁of ▁light ▁intensity ▁in ▁the ▁back sc atter ing ▁direction . ▁This ▁substantial ▁enh ancement ▁is ▁called ▁the ▁cone ▁of ▁coh er ent ▁back sc atter ing . ▁ ▁C oh er ent ▁back sc atter ing ▁has ▁its ▁origin ▁in ▁the ▁inter ference ▁between ▁direct ▁and ▁reverse ▁paths ▁in ▁the ▁back sc atter ing ▁direction . ▁When ▁a ▁multiply ▁scatter ing ▁medium ▁is ▁ill umin ated ▁by ▁a ▁las er