Yes, you'll get 100% of whatever the supply voltage is, in this case 12V. You are right kessil expects 10V. I use lm2596 (I buy them in 6 packs, so have always few spare) to convert 12V to 10V. But if you dont have those, you can also use a coule of resistor (like one 1K, and one 5K) to create a voltage divider which will convert the 12V to 10V, and then feed that 10V to npn emitter pin , where you have connected the 12v in right now... and voila... you have a spectral controller

I am happy that you got thw pi pwm going, you know this is a significant futuristic thing

, earlier this year broadcom (Pi's original CPU chip maker) opened up the pin specification for hardware timer, it took another three months to percolate that information through Raspberry Pi kernel and software stack so that we can use the pwm, and I think sometime in Apirl or May I added the support for Pi pwm.. its fresh from the oven

. Its a big deal I think, because now one can make a two part doser or a kessil controller just using a pi zero, since we have two pwm.. without the need of pca9685 , this reduced the build cost by at least 12$ and less complexity/wiring/power consumption. One of the original goal of reef-pi is to make reef tank controllers affordable, I wont say we are there yet, but this is a significant milestone, and seeing it working for you (we still have some work to do) makes me very very excited
thanks again for testing it out