NET Bible Hebrews 1:3 The Son is the radiance [ie: reflection] of his glory and the representation of his essence, and he sustains all things by his [ie: God's] powerful word, and so when he had accomplished cleansing for sins, he sat down at the right hand of the Majesty on high.
Compare:
Wisdom of Solomon 7: 25 For she is the breath of the power of God, and a pure influence flowing from the glory of the Almighty: therefore can no defiled thing fall into her. 26 For she is the brightness of the everlasting light, the unspotted mirror of the power of God, and the image of his goodness.
The Cambridge Paragraph Bible: of the Authorized English Version. (1873). (Wis 7:24–26). Cambridge: Cambridge University Press.
"she is the breath of the power of God" -> "he sustains all things by his [God's] powerful word"
"she is the brightness of the everlasting light, the unspotted mirror of the power of God" -> "the radiance [ie: reflection] of his glory"
"a pure influence flowing from the glory of the Almighty" -> "the representation of his essence"