Abu Sa’eed al-Khudri  (May Allah be pleased with him) said:-

“Whoever reads Surah al-Kahf on the night of Jumu’ah, will have a light that will stretch between him and the Ancient House (the Ka’bah).” 

(Narrated by al-Daarimi# 3407. This hadeeth was classed as saheeh by Shaykh al-Albaani in Saheeh al-Jaami, 6471)

“Whoever reads Surah Al-Kahf on the day of Jumu’ah, will have a light that will shine from him from one Friday to the next.”

(Narrated by al-Haakim, 2/399; al-Bayhaqi, 3/249. It was classed as saheeh by Shaykh al-Albaani in Saheeh al-Jaami’, 6470)

Note:-The surah may be read during the night or the day of Jumu’ah. The night of Jumu’ah starts from sunset on Thursday, and the day of Jumu’ah ends at sunset. Therefore the time for reading this surah extends from sunset on Thursday to sunset on Friday.