Got a window with no view but in a room that benefits from daylighting? You try to dress up the window with blinds or curtains, but it still hurts the senses like a sore thumb. (Metal Venetian blinds can be tilted to not only cover the ugly view but also deflect light deep into the space.) One option is a colorful window film ~ get one with UV blocking if you also want to eliminate solar heat gain in the summer.
Of course, the most energy-efficient solution is to fill out the window with insulation, seal it airtight, and put a tapestry over the opening. That being the case, nobody wants to live in a cave. Natural lighting not only saves on artificial lighting costs but connects you to the natural rhythm of the solar day. The trick is to have a balance between the window area and daylighting.