Data Sheet

6/30/2015 LightemittingDiodes(LEDs)learn.sparkfun.com
https://learn.sparkfun.com/tutorials/lightemittingdiodesleds?_ga=1.43468261.1900427809.1434378181 11/13
other,releasingenergyintheprocess.Inmostdiodesthatenergyleavesasheat,butinLEDsthat
energyisdissipatedaslight!
Thewavelengthoflight,andthereforethecolor,dependsonthetypeofsemiconductormaterialused
tomakethediode.That’sbecausetheenergybandstructureofsemiconductorsdiffersbetween
materials,sophotonsareemittedwithdifferingfrequencies.Here’satableofcommonLED
semiconductorsbyfrequency:
Truncatedtableofsemiconductormaterialsbycolor.ThefulltableisavailableontheWikipediaentry
for“LED”
Whilethewavelengthofthelightdependsonthebandgapofthesemiconductor,theintensity
dependsontheamountofpowerbeingpushedthroughthediode.Wetalkedaboutluminousintensity
alittlebitinaprevioussection,butthere’smoretoitthanjustputtinganumberonhowbright
somethinglooks.
Theunitformeasuringluminousintensityiscalledthecandela,althoughwhenyou’retalkingabout
theintensityofasingleLEDyou’reusuallyinthemillicandelarange.Theinterestingthingaboutthis
unitisthatitisn’treallyameasureoftheamountoflightenergy,butanactualmeasureof
“brightness”.Thisisachievedbytakingthepoweremittedinaparticulardirectionandweightingthat
numberbytheluminosityfunctionofthelight.Thehumaneyeismoresensitivetosomewavelengths
oflightthanothers,andtheluminosityfunctionisastandardizedmodelthataccountsforthat
sensitivity.
TheluminousintesityofLEDscanrangefromthetenstothetensofthousandsofmillicandela.The
powerlightonyourTVisprobablyabout100mcd,whereasagoodflashlightmightbe20,000mcd.
Lookingstraightintoanythingbrighterthanafewthousandmillicandelacanbepainful;don’ttryit.