Noor of your face
:salam2: brother
if we read the following verse in Quran...
4:174 O MANKIND! A manifestation of the truth has now come unto you from your Sustainer, and We have sent down unto you a clear light.
So the guidance of Allah swt is described as light .....Why ? because it lighten the hearts of people ...by Truth (opposite of ignorance) ..Truth about who is their creator, what is his noble perfect attribtes , how to live a pure decent life full of light and happiness....being close to Allah swt; (Allah is the light of heavens and earth.....)
More on the day of judgment Allah swt told about the believers:
57:12 on the Day when thou shalt see all believing men and believing women, with their light spreading rapidly before them and on their right, [and with this wel*!come awaiting them:] “A glad tiding for you today: gardens through which running waters flow, therein to abide! This, this is the triumph supreme!”
(I pray to Allah swt to make us among them)
I think light on your face is dervied from such high bright meanings ......when their is light of faith within then it will flow outside on faces....and Allah swt knows best.