Venetian or horizontal blinds allow you to set the slats at any angle, but homeowners debate whether the slats should be angled down or up. Depending upon your goal, you may opt to turn the slats in either direction. "Angled down" refers to the slats sloping downward into the room, allowing sunlight to spill toward the floor. "Angled up" refers to the slats sloping down toward the ground outside, so that the inside slat edges are higher than the window-side slat edges.
If you're concerned about privacy, you'll choose your slat angle based upon your floor or level. When you're not at ground level, the angle matters. If your window is on the second story, keep your slats angled down into the room to prevent people on the street from seeing directly up into your room. If your window is on the first story, it won't matter which way the slats are angled. If your window is in the basement, keep the slats angled up.
Blind retailers and decorating magazines typically photograph horizontal blinds with the slats angled down. On some faux wood blinds, only the top of the slats are finished. Angling the slats up and exposing the unfinished edge would cheapen the overall appearance of the window.
Blinds allow homeowners the freedom to control how much light enters the room. By angling the slats down, you'll maintain some privacy while allowing light to spill into the room. When the slats are angled up, you'll achieve greater light blockage. To thwart morning light in bedrooms, keep the slats angled up and tightly shut.
If you own pets that enjoy viewing the great outdoors, keep the slats angled up on the first floor so that they can watch wildlife scamper on the ground. Keeping the slats angled up can also protect your furniture and carpet from fading. If a heat or air conditioning vent lies on the floor below a window, angling your slats up works to prevent air from being directed out the window. However, you can use your blinds to strategically direct light toward floor plants by angling the slats down.