LCD projects the image at a very low luminosity

If you feel confident you didn't damage anything when repairing the device I would reccomend going over cable connections again to ensure you have properly seated all cables correctly. Check the display brightness setting as well to ensure it wasn't lowered for whatever reason.

Also, If the ipad was not turned off during repairs (always power off devices before you open them) when the LCD is disconnected sometimes it wont function properly after reinstall. disconnect the battery for a few seconds via the cable connecting the power board to the main board. you may also try a hard reset. This has cured the same issue for me many times.