White BalanceIn theory, having the three LEDs at full intensity must produce a perfect white beam. In practice that is not true in most cases due to physical factors.
To overcome this problem, we need to perform a "white balance" adjustment. This consists of making corrections to the maximum brightness of each LED so they produce a real white (or closed to it) when set to their saturated values.
White balance adjustment can be done either by Software or by Hardware.
By Software
For small systems (a single light canon as we have been discussing so far), software white balance adjustment could prove more convenient because it simplifies the circuitry.
It is done by establishing upper limits for variables R, G, and B (that is less than 255) in software. Once these limits have been set, the program will never attempt to set values beyond those so saturated R, G and B will result in an acceptable white beam.
White balance adjustment must be done using the controls available to the user. The exact procedure has not been designed yet.
By Hardware
For large systems, an analog approach may prove better. Imagine a scenario in which a single "control module" is sending three PWM signals (R,G,B) to various (possibly large) LED modules in a daisy chain fashion.
In this case, white balance is done separately in each module by varying the current supplied to each triad when receiving signals of maximum value (maximum duty cycle). Possibly three pots per module are employed to make the adjustment, one per color (RGB).
NOTE:
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Actually, "maximun duty cycle" means DC. So white balance can be done in LED modules individually whithout having to be connected to the "controller board". Maybe, by actuating switch labeled "White" inputs get fed with DC so the adjustment can be done in this conditions.
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