Keep the space dark, no matter the time of day or night.

Eliminate any and all lights from the outside.  Block street lamps, residential lights or any other obtrusive lights (good morning sunshine!). Side channels will finish the job, eliminating 99.9% of incoming light.  The most recommended option for bedrooms, conference or media rooms.  For double duty, pair a Light Filtering Shade with a Blackout.  Blackout materials come in many textures and colors, all with 0% transparency.  These types of shades can also further help to lower energy bills due to heat reflection and help qualification for ygreen or other programs..