KnowHow team explains: A phenomenon called phosphorescence is responsible for the light that most glow-in-the-dark items emit.

Phosphorescence occurs when light absorbed by an object is slowly released and can be observed even after the light source has been removed. If not tampered with, such light is dim and pale blue in colour.

Chemists had the bright idea to make this phenomenon visually stimulating. They discovered that when the phosphorescent material was mixed with fluorescent dyes, the object emitted a glowing bright green or sometimes red light.

The reason for this transformation is that fluorescent compounds absorb light and rapidly emit it, giving the compounds a glowing appearance. However, this phenomenon occurs only in the constant presence of the original light source.

The pale blue light emitted by the phosphorescent material is, in turn, absorbed by the fluorescent dye. And the light now emitted is green or red, depending on the type of dye used.

The most commonly used phosphorescent material is zinc sulphide mixed with copper, and the green fluorescent dye is mostly sodium fluorescein. Likewise, the red fluorescent dye is usually rhodamine. Paired together, the phosphorescent and fluorescent materials produce a ghostly, glowing green or red light, which is often used to make toys and decorative items attractive.