As you may know, kennings in Old English/Anglo-Saxon literature (and other Germanic literatures) are usually compounds of two or more words, sometimes whole phrases, that stand for single nouns in Modern English. For example, in several places in Beowulf where the poet refers to the sea, we see the kenning whale-road and swan-road or he might refer to a high-ranking queen as peace-giver, a poetic way of creating an image that would resonate with readers or listeners. A listener, for example, might not be familiar with the word sea or ocean, but he or she would understand what the whale-road means because everyone in that society was familiar with such images.
In the two lines you've asked about, the kenning is in line 545, "Heaven's Own candle," which stands for the sun--comparing the brightness of the light in the hall to the brightness of the sun. In another section of Beowulf, the sun is referred to as "God's bright beacon," another kenning much like "Heaven's own candle."