Blackout means near-total light blockage
If your needs for darkening are based on a night shift and you have a window that gets direct light, you’ll probably want a full blackout window blinds. Blackout means near-total light blockage and it differs from what is called ‘room darkening’ window treatments. White technically there will still be some light leakage (1-3%), the light blockage is effectively total and there is little difference (in regard to light) between installing a quality blackout window treatment and putting up a solid wall. However, there is a huge difference when you want to look out that same window, get some ventilation or match your decor. This is why blackout window treatments exist and why they are so valuable.