Here are perhaps slightly better metaphors by Tertullian:
"When a ray is projected from the sun, it is a portion of the whole; but the sun will be in the ray, because it is the sun's ray, nor is it a division of nature, but an extension. Spirit from Spirit, God from God?as light is lit from light. The source of the substance remains whole and undiminished even if you borrow many offshoots of its quality from it. Thus what has proceeded from God, is God and God's Son, and both are one. Thus Spirit from Spirit, God from God?it makes in mode a double number, in order not in condition, not departing from the source but proceeding from it. This ray of God, as was ever foretold in time past, entered into a certain virgin, and, in her womb fashioned into flesh, is born, man mingled with God. The flesh informed by the spirit is nourished, grows to manhood, speaks, teaches, acts?and is Christ." (Tertullian, Apologeticus 21.10-14).
"Now the Word was formed by Spirit, and Spirit is, so to speak, the body of the Word. Therefore the Word is always in the Father; 'I in the Father' and 'with the Father' . . . and never separated or apart from the Father. . . .This will be the 'projection' of truth, the safeguard of unity, by which we say that the Son was produced from the Father, but not separated from him. For God produced the Word, as the Paraclete also teaches, as a root produces the shoot, a spring the river, the sun a ray: for these manifestations are 'projections' of those substances from which they proceed. I would not hesitate to call a shoot 'the son of a root,' a river 'the son of a spring,' a ray 'a son of the Sun.' For every original source is a parent, and what is produced is its offspring. Much more is this true of the Word of God, who has received the name of Son as his proper designation; but the shoot is not detached from the root, nor is the Word detached from God" (Tertullian, Adversus Praxean, 8).
"Everything that proceeds from anything must needs be another thing, but it is not therefore separate. When there is one other, there are two; when there is a third, there are three. The Spirit makes the third from God and the Son, as the fruit from the shoot is the third from the tree, the canal from the river is the third from the source, the point of focus of a ray third from the sun. But none of those is divorced from the origin from which it derives its own qualities. Thus the Trinity derives from the Father by continuous and connected steps" (Tertullian, Adversus Praxean, 8).
Note however that these metaphors assume an economical Trinity and not the ontological Trinity of the Nicene period which argued that the Son, the Father, and the Holy Spirit were co-eternal and co-equal. What Tertullian was working on in these texts is showing distinction-within-unity, that there can be individuality without division. This refutes both the modalist (which denied distinction) and the Praxean (which specified seperation) positions.