Luminous sunglasses lenses

Luminous sunglasses is a kind of normal sunglasses with special luminous lenses inside. And with this kind of sunglasses, you can know each card just like face up. If you never use marked cards, it is the most useful defensive tool during the poker game in private place or casino.

It is common for gamblers to wear sunglasses while playing cards, just watch the annual 'World Series of Poker" at Binion's Horseshoe in Las Vegas. Gamblers do not want other players to look at their eyes and "read" emotion or discover "tells". When doing magic people cannot see you looking at the back of cards.
Gimmick may be used to find out if your "friends" are using these marked cards against you in a game of poker, rummy, etc. Similar to how a casino may use the same gimmick to detect if this marking technique is being used against them. Think of the fun you can have if you can read your friends marked cards and they do not know that you too can see the marks.