The issue with daylight is that it fluctuates, as you said, it's not easily controlled. A 4700K Incandescent bulb, on the other hand, might be something you can control with a feedback circuit or voltage regulator. If I were setting up a standard box, I'd make it one brightness, a standard, and then modify its brightness outside the box on the bench. You could use the old GE meter to monitor the brightness inside the box.