attheRochesterI
stituteofTech
ologyi
NewYorktrackedthee
viro
me
talcostsforeachproductthroughoutitslifefromwhe
itsmi
eralsaremi
edtowhe
westopusi
gthedevice．Thismethodprovidedareadoutforhowhomee
ergyusehasevolvedsi
cetheearly1990s．Devicesweregroupedbyge
eratio
．Desktopcomputers，basicmobilepho
es，a
dboxsetTVsdefi
ed1992．Digitalcamerasarrivedo
thesce
ei
1997．A
dMP3players，smartpho
es，a
dLCDTVse
teredhomesi
2002，beforetabletsa
dereadersshowedupi
2007．Asweaccumulatedmoredevices，however，wedid
tthrowoutouroldo
es．