On the back of the banknotes there are designs printed with fluorescent ink, which glow when placed against ultraviolet light (also known as “black light”). The new 50-peso banknote has two fluorescent inks.

Cotton paper banknotes they have color fibers on both sides—that is, tiny fibers embedded in the paper and distributed randomly. These fibers are fluorescent and can only be seen under black light.

In case of 100-, 200-, 500-, and 1000-peso banknotes, the 3D-thread also shines when a banknote is placed under a black light.