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Well, some natural sunlight would be good for them IF a) it doesn't overheat the brooder and b) if the glass doesn't filter out the good part of the UV light -- many types of energy efficient glass filter out the parts of the spectrum that make vitamins in the birds bodies).
Overall, not necessary, but if practical to do so, probably nice for them to see the sun at times. I know my birds like to sunbathe, even when fairly young, like 6 weeks.
Unfortunately, my chicks don't get any natural light until I take 'em outside for short "day trips." I do that so they WILL get some outdoors time AND some natural light.