Quote Originally Posted by cnmne View Post
My experience is that the spectral output of common blue LEDs is too wide to obtain a grade 5 contrast. If you can live with grade 4 maximum, it might be fine.
There are two, maybe three LEDs emitting blue light at slightly different wavelengths - It would help if there was a decent spectral response graph available so that "we" could say "to get grade N, you need wavelength Y" for the average VC paper.

Quote Originally Posted by ic-racer View Post
It still seems to me that a timer circuit is easier to build (or buy) than a PWM dimmer. So, instead of setting blue and green intensity you set blue and green time. Basically it would could be split grade printing with the push of a single button.
But, but... You already have a computer in front of you. A little bit of code, and a few extra minutes with a soldering iron, and you have a high precision timer