I have LED lights which have a switch Veg & Bloom and according to the manufacturer's directions, the Veg side turns on more of the Blue lighting, and then the Bloom switch turns on the other 50% of the light which is more in the Red wavelength... but in Bloom they want both switches to be on together so you get Veg & Bloom... and at one point I wondered if it really does make a difference. So I did a bit of an experiment to find out. The short of it is simply this, the Blue & Red will gave me extremely dense foliage and the plants did the absolute best with the two switches on, and I had issues of with the plants not really getting the light penetration without the Blue and I lacked -50% less foliage and bud as a result of my experiment with just the Red (Bloom switch) being on... so I won't try that again.
Another one I tried at another point was to use a "Construction LED" light that looks like the halogen construction lights, which was seriously in the Blue spectrum and extremely bright, I figured more Blue light during Bloom would help get denser foliage yet and maybe even more buds still. Instead what happened was in the middle of flower, I turned the plants back to Veg in 24-48 hours time because of my experiment, but I learned a lesson as to the sheer importance of the right colors of light at the right times and that they must be in balance for the best results.