Blacking out windows can be achieved with several methods. For a permanent solution, use blackout curtains or shades, which block all light when installed properly. You can also apply a blackout window film to the glass itself, or use temporary solutions like blackout liners or foam board. Ensure that the chosen method covers the entire window area to prevent any light leaks for complete darkness.

Use blackout curtains, shades, or films for a permanent blackout effect. Temporary solutions like liners or foam boards can also be effective.