Java fern can live up to seven days without light. This aquatic plant is extremely hardy and can tolerate a wide range of conditions, so it should be able to survive up to a week with no light at all.
However, while Java ferns prefer low to moderate lighting, they will eventually wilt if left without any light for too long.
To keep your Java fern healthy, make sure it gets anywhere around 6–10 hours of light each day. Also, providing only 1.5–2 watts of light for each gallon of water is recommended. If the lighting is too intense, the fern’s leaves might burn, causing them to turn brown or transparent.