We live in SW AZ and window coverings are super important to keeping out the heat.  Our guest room has been long neglected in that area.  We had blinds in there and even covered the window in cardboard but that particular room was just always stuffy and HOT.  We finally got these room darkening curtains for that room and the change is amazing!  I will admit that at first glance, it still seemed like a good bit of light was getting through.  But within just a few hours, the temperature change in the room was noticeable.  The room is comfortable now, even without a fan going (which was a necessity before).  These curtains have made such a big difference and made the room so much more welcoming to our guests.