bldc blower and light sensor

• In the Philips home electronics hobbyist kit (other manufacturers' kits are available) dating from 1965 was a thing called a 'light-dependent resistor'.
• In older clockwork cameras such as the Zenith (other clockwork camera manufacturers are available), there is a light-to-voltage generating device that drives the indicator to form a light meter that is used to set the aperture and the shutter speed.
• Most solar cells have an output that is roughly proportional to the brightness of the incident light.

If any of these could be used as a primary measuring element, the rest is transistors and capacitors and all that sort of stuff. Make a 4-20mA signal from it, and bung it into the variable speed drive that runs the blower.

You can use a photodiode, Motorola, now ON, makes many, and apply this to the input of an op-amp making a non-inverting amplifier. Use the potentiometer as the negative feedback resistor to change the gain. The output from the op-amp could drive a transistor-based output section, depending on how much power you need. This output section assumes a DC blower (you didn't mention). For AC the photodiode and op-amp would still apply, but your output would be SCR or Triac based. The Motorola data book usually gives application information for the photo diode section, and I know the books of other manufacturers do the same.

Good luck,

Bluezone