You still have to use UV bulbs. I have my chams in front of a south facing sliding glass door system. During the winter when the sun shines in from about 11 am to sundown, I shut off the basking lights. They are generally on for 2-3 hours in the morning so my little ones can warm up from the night and digest their food. They really like the window and you can find them all looking out all day long. In the afternoon they sometimes come down and rest in the leaves because it does get warm from the sun. I choose this time to give them a misting, especially if I find them with their mouths open.
I guess what I'm saying is if you are able to monitor your chams then putting them in your window would be a good thing. If you are going to work and just leaving them I would be a little concerned unless you have a large plant that will cast some shade outside the enclosure as well as plants inside the enclosure. Having the shade gives them a break from the heat if the sun does come into the window. Don't forget to leave the UV on for 12 hours.
