In general, daub is the hustlers' term for any kind of substance that can be used to stain the backs of playing cards with the purpose of making marked cards, in the course of a card game, while playing with someone else's deck. While regular daub can be substituted by using any kind of substance that happens to be available, such as lipstick, cigarette ash, tobacco stains, etc, luminous daub is more of a laboratory product that cannot be put together on the fly.
Luminous daub is used to produce the type of marked cards sometimes called luminous readers. To read the work one is required to use a pair of luminous glasses or contact lenses. In the West luminous systems are typically used to cheat at poker and blackjack, but in Asia they are also frequently used to cheat at other card games. In 2008 an Asian crooked gambling ring was busted; the original news story is archived on this site under Korean Crooked Gambling Bust (although they only show how the cards were marked for cheating at poker).
The image below shows an assortment of three kinds of luminous daub. The two smaller vials contain two kinds of daubs that are technologically quite advanced. At the time of this writing they are the best luminous daubs available anywhere and are the types of daub especially made for the Black Predator luminous system. The larger vial on the right side contains an old daub, which is basically a green pigment that was made to be used with conventional red-lens luminous systems. By today's standards those systems are outdated and considered to be quite primitive as they work solely on the principle of color blocking; not to mention that no one can seriously consider wearing red glasses to a poker game. The powder inside that vial actually came form a larger quantity that was given to me many years ago. I've transferred a smaller amount into a this vial; this small amount actually makes up a lifetime supply of daub.
The daubs in these vials are all powders. These can be used in a number of different ways, but one clever way to use green powdered daubs is to smear a small amount over the back of a US banknote (the green side). There are some other ways to use powdered daubs, but perhaps it is better not to reveal the details. You will notice, however, that the vial in the center contains a dark-red powder.
Since these are powders they can be mixed with a liquid medium to produce luminous ink. However, ink made from these powders will not produce the best results. The ink made for the Black Predator luminous system has a slightly different active ingredient. The old daub is actually the same powder that was used to make luminous ink at the time when advanced technology was not available, but the ink made from this daub is just not too good. At that time luminous systems were still somewhat of a joke, actually.