Among the hadiths mentioned about the virtues of Surat Al Kahf is what Abu Darda’ reported from Allah’s Messenger (?) as saying:
“If anyone learns by heart the first ten verses of the Surah al-Kahf, he will be protected from the Dajjal.” [Sahih Muslim]
Of course, the trial of the Dajjal is among the biggest trials believers would face, and knowing that Surat Al Kahf provides this protection must make it of extremely high value to the believers.
Additionally, in another hadith, Al-Bara’ ibn ‘Azib reported that a man was reciting Surat al-Kahf and in his barn was an animal which became unsettled. As he looked, there was a mist or a cloud overshadowing him. He mentioned that to the Prophet and he said,
“Continue reciting, for it was calm which descended with the Quran, or for the Quran.” [Sahih Al Bukari & Muslim]
The Light of Surat Al-Kahf
Regarding your questions, it was mentioned in the hadith from Abu Sa’id Al-Khudri that the Prophet said,
“Whoever recites Surat al-Kahf on Friday will have a light between this Friday and the next.”
Some words of advice
Having said that, as an advice, if you do know that it takes you a long time to read it or that you might not be able to finish it if you start from the Fajr of Friday. Then, you can start reading from the Maghrib of the night before, i.e. from the Maghrib of Thursday.
We have from after the Maghrib of Thursday until the Maghrib of Friday to read, and alhamduliAllah this is a vast time for us to engage in the remembrance of Allah and read Surat Al Kahf.
Regarding your other question on describing the light in the hadith. The scholars have mentioned two possibilities for that: either this is a metaphorical light. Meaning it’s the light of guidance and prevention from falling into big sins that decrease one’s light of faith…etc. So it is a guiding light towards the straight path and away from sins.
Or, an actual light, meaning, the person will have light and brightness in their face here and in the hereafter. They’ll have light from under their feet guiding their path on the Day of Judgement.
We know that there is darkness on the Day of Judgement. So, having light under one’s feet guiding their way is a major blessing and means of security.