I need to illuminate a 10 cm x 10 cm PVC sheet, underwater, while maintaining a fairly precise light intensity between 0 and 30 lux. I had planned to use LEDs and regulating light intensity with PWM, but white LEDs seem to have a fairly high minimum brightness. In addition, LEDs are directional, and mounting them the way I had originally planned would have the light directed upward, away from the sheet. I considered mounting the LEDs such that they would be directed back toward the PVC sheet, but I could not find a way to adequately mount the LEDs while also maintaining a fairly low profile (one such design involved mounting the LEDs 27 cm above the PVC sheet).
I wondered if anyone had any solutions to this problem. I would prefer white light and direct current, but there is room for flexibility in those regards.