Umthamo wokwelapha okulula ubalwa ngale fomula:
Ubuningi Bamandla x Isikhathi = Umthamo
Ngenhlanhla, izifundo zakamuva zisebenzisa amayunithi ajwayelekile ukuchaza inqubo yawo:
Ubuningi Bamandla ku-mW/cm² (ama-milliwatts ngesentimitha ngalinye ayisikwele)
Isikhathi ku-s (amasekhondi)
Isilinganiso ku-J/cm² (amaJoules ngesentimitha ngalinye ayisikwele)
Ukuze welashwe ngokukhanya ekhaya, ubuningi bamandla ngakho-ke yinto eyinhloko okudingeka uyazi - uma ungazi, ngeke ukwazi ukwazi ukuthi uzosebenzisa isikhathi esingakanani idivayisi yakho ukuze uthole umthamo othile. Kumane kuyindlela yokulinganisa ukuthi ubukhali bokukhanya buqine kangakanani (noma ukuthi zingaki ama-photon endaweni ethile).
Ngama-LED akhiphayo ane-engile, ukukhanya kusabalala njengoba kuhamba, kumboze indawo ebanzi nebanzi. Lokhu kusho ukuthi ukuqina kokukhanya okulinganiselwe kunoma yiliphi iphuzu kuba buthakathaka njengoba ibanga ukusuka emthonjeni likhula. Umehluko kuma-engeli okukhanya kuma-LED nawo uthinta ubuningi bamandla. Isibonelo, i-LED engu-3w/10° izokhombisa ubuningi bamandla okukhanya kakhulu kune-LED engu-3w/120°, ezoveza ukukhanya okubuthakathaka endaweni enkulu.
Izifundo zokwelapha ngokukhanya zivame ukusebenzisa ubuningi bamandla obungu-~10mW/cm² kuze kufike ku-max ~200mW/cm².
Umthamo umane ukutshela ukuthi kusetshenziswe isikhathi esingakanani lokho kuqina kwamandla. Ukukhanya okuphezulu kusho ukuthi kudingeka isikhathi esincane sokufaka:
I-5mW/cm² esetshenziswa imizuzwana engama-200 inikeza i-1J/cm².
I-20mW/cm² esetshenziswa imizuzwana engama-50 inikeza i-1J/cm².
I-100mW/cm² esetshenziswa imizuzwana eyi-10 inikeza i-1J/cm².
Lawa mayunithi e-mW/cm² namasekhondi anikeza umphumela ku-mJ/cm² – vele uphindaphinde lokho ngo-0.001 ukuze uthole ku-J/cm². Ngakho-ke ifomula ephelele, uma ucabangela amayunithi ajwayelekile ithi:
Umthamo = Ubuningi Bamandla x Isikhathi x 0.001