Then they enter a tunnel equipped with a black light, which makes any remaining lotion glow.
From the usatoday.com
The students were asked to coat their hands in a clear lotion that can only be seen under a black light.
From the abcnews.go.com
When the students lined up with their hands out, the black light revealed that most of them still had plenty of lotion on their hands.
From the abcnews.go.com
Most bitter for Sandy is the father who loves her but slips her skin-lightening lotion, has her jailed when she becomes involved with a black man, and ultimately disowns her.