ogen ▁l amps ▁have ▁the ▁advantage ▁of ▁deliver ing ▁high ▁power ▁for ▁a ▁relatively ▁low ▁cost . ▁Using ▁different ▁band - pass ▁filters , ▁the ▁same ▁source ▁can ▁be ▁used ▁to ▁produce ▁several ▁exc itation ▁channels ▁from ▁the ▁U V ▁to ▁the ▁near ▁inf ra red . ▁Light - em itting ▁di odes ▁( LED s ) ▁have ▁become ▁very ▁popular ▁for ▁low ▁cost ▁broad ▁band ▁ill um ination ▁and ▁narrow ▁band ▁exc itation ▁in ▁F GS . ▁Because ▁of ▁their ▁characteristic ▁light ▁emission ▁spectrum , ▁a ▁narrow ▁range ▁of ▁w avel ength s ▁that ▁matches ▁the ▁absor ption ▁spectrum ▁of ▁a ▁given ▁flu or oph ore ▁can ▁be ▁selected ▁without ▁using ▁a ▁filter , ▁further ▁reducing ▁the ▁complexity ▁of ▁the ▁optical ▁system . ▁Both ▁hal ogen ▁l amps ▁and ▁LED s ▁are ▁suitable ▁for ▁white ▁light ▁ill um ination ▁of ▁the ▁sample . ▁Ex c itation ▁can ▁also ▁be ▁performed ▁using ▁las er ▁di odes , ▁particularly ▁when ▁high ▁power ▁over ▁a ▁short ▁w avel ength ▁range ▁( typ ically ▁ 5 - 1 0   nm ) ▁is ▁needed . ▁In ▁this ▁case ▁the ▁system ▁has ▁to ▁account ▁for ▁the ▁limits ▁of ▁expos ure ▁to ▁las er ▁radiation . ▁ ▁D ete ction ▁techniques ▁ ▁Live ▁images ▁from ▁the ▁flu ores cent ▁d ye ▁and ▁the ▁surg ical ▁field ▁are ▁obtained ▁using ▁a ▁combination ▁of ▁filters , ▁l enses ▁and ▁cam eras . ▁During ▁open ▁surg ery , ▁hand ▁held ▁devices ▁are ▁usually ▁preferred ▁for ▁their ▁ease ▁of ▁use ▁and ▁mob