Illuminating a PVC sheet, maintaining specific light intensity

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.

It's just a matter of getting the right program in the Ardiuno.

Paul

How about using White LED strips?

I guess Vaethas needs to study up on LEDs. They are "point source" of light. In other words, they illuminate equally in ALL directions. The packages you purchase cheaply has a shape that concentrates the light to a lens on the tip end. Other packages have other shapes. Some surface mount LEDs have no lens at all, so just the light from the LED point is seen.

There are NO "white". LEDs. Our eyes/brain is deceived into thinking we are seeing white light. There are actually two LEDs in the package emitting two different UV wave lengths of light. When those photons strike a phosphor combination coating, it emits a yellow light and another I can't recall right now. Those two wavelengths plus the blue residual from the UV LEDs is the actual light. That is why the "white" light has a high minimum brightness. The phosphors don't work below some minimum illumination.

Paul