Ambient room light is sufficient. I spent the 60's and 70's with a single 40W incandescent on a 20-gal and rarely had the light turned on. When I did, it was only for a few hours at night and not many nights at that. I was able to "grow" Anacharis, Cabomba and a few others whose names I no longer recall. In fact, even with high-tech, one of the reasons I run CO2 24/7 is because plants awaken almost at the moment of sunrise with the ambient light. I parenthetically called it "grow" because the growth was almost imperceptible. It was more surviving, but the plants did not deteriorate.
Regarding spectrum, I did do some crude experiments with the blue spectrum and did find that GSA increased at lower levels when I added blue. Increased red did not seem to impact algae. This might be expected because the blue wavelengths penetrate much more than the reds. I did not see any unusual development in hair algae or GDA. Again, this was a very crude experiment, although I did repeat the process several times. Other parameters probably influenced the outcome somewhat.