I love this vegan brightening sheet mask from Andalou Naturals. It contains aloe, tamarind, and vitamin C. 
At first, I thought this mask was like any another sheet mask. But, it worked great. 

This sheet mask started to tighten my skin within few minutes and my skin was dramatically brighter this morning. No difference in dark spots though. This mask sheet is also very hydrating; my skin was very soft after using it. I suggest using it at night, so the natural ingredients can be absorbed by the skin when it goes into repair mode at night.

This sheet mask is made without sulfates, GMOs, petrochemicals, phthalates, parabens, synthetic fragrance, colors or preservatives.
It is a single-use sheet mask, so I think using it once a week will lighten dark spots over time. I bought this sheet mask at Whole Foods for $6. You can also find it on Amazon by clicking here.