Id prprobably suggest meanwell hlg120h-54A (assuming the board is 54V, cant quite remember). A-type driver lets you dim to half power using on board dials for about 75w output. But that might ve too much for a small seedling, at least make sure you hang the light high over an immature plant as it could get fried with too much light. B-type driver would work to dim to 10% but would be able to drive the board til 2100ma as its voltage is capped at 54v.
Also, would recommend using a sheet of 2-3mm of alu as heatsink for high wattage operation.
At 2100ma you need the light about 50cm or more for a mature auto, rough calculation.