Four models live in Lumen's Image Generator. Pick by what you're making:

Style references

Upload a single image that captures the visual world you want — colour palette, lighting, materials. Lumen will pull from it without copying it.

Character references

Upload a single image of a face or character. Lumen keeps that character consistent across every variation.

Aspects, count, seed

Default count of 4 gives you good variety. Lock the seed once you find a generation you like and re-render variations — same seed, slightly different prompts.