What We Found
Pure bamboo woven blinds (without blackout lining) do not provide effective blackout. Light passes through the weave gaps. For true blackout, you need either a fabric blackout curtain layered over bamboo blinds, or bamboo blinds with a thermal lining (which defeats the point of natural bamboo).
The practical recommendation: use bamboo blinds for privacy and partial light reduction (approximately 40-60% light blocking), and add a separate blackout curtain liner if you need complete darkness for shift workers or light-sensitive sleepers.