How to prevent bright flashing lights, such as at a nightclub, from shining through the windows to the outside

Method 1: Try using a tint meter to know how much light needs to be filtered out. If the glass is dual-pane or Low E glass, it’s best not to go any darker than 25% if it gets direct sunlight, especially in hot climates. It will almost definitely overheat and crack and/or shatter eventually. If it’s not in direct sunlight then a blackout reflective film should do the trick. You could also use a whiteout or frosted product on the other side of the film to help the tint filter out light without making the glass too hot.