How could the Kohen Gadol see when he went in the Holy of Holies?

Question

Jewish Encylcopedia speaks about the Holy of Holies and says (in part):

In Solomon's Temple the Holy of Holies formed a part of the house of Hashem...... The section farthest from the entrance, designated also as the "debir" (the "oracle" "the most holy place," I Kings vi. 5), was 20 cubits high and presented the shape of a cube. The stone of this inner or hinder part, like the outer room, was completely hidden with cedar boards carved with knops or gourds and open flowers and then covered with pure gold. This room must have been without light.

So how could the Kohen Gadol see when he went in there?

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Answer 1

Yerushalmi Yoma 5:3:

תני עד שלא ניטל הארון היה יוצא ונכנס לאורו של ארון משניטל הארון היה מגשש ונכנס מגשש ויוצא

Translation: We learnt that before the aron was taken away, he would go in and out by the light of the aron. After the aron was taken away, he would feel his way in and feel his way out.