This work, likely a lyrical piece for harp or piano, evokes a gentle and flowing atmosphere. Its charm lies in its expressive melody and delicate arpeggiated accompaniment.
Focus on creating a singing tone and sensitive phrasing with appropriate rubato.
Aussitôt que la Lumière is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
Aussitôt que la Lumière is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.