Many vibrant neon colors glow under a black light. A black light emits ultraviolet (UV) light, which is invisible to the human eye. When this UV light strikes certain materials, including many neon colors, those materials absorb the UV energy and then re-emit it as visible light, creating the glowing effect.
The Science of Fluorescence
The glow observed in neon colors under a black light is a result of a physical process called fluorescence. Black lights primarily produce ultraviolet-A (UV-A) light, a portion of the electromagnetic spectrum with wavelengths longer than UV-B or UV-C. When UV-A photons from a black light encounter a fluorescent substance, the electrons within that substance absorb the energy from these photons.
This absorbed energy temporarily boosts the electrons to a higher energy level, placing them in an “excited state.” This excited state is unstable, and the electrons quickly return to their original, lower energy state. As they fall back, they release the absorbed energy in the form of light at a longer wavelength, making it visible.
This re-emission of light happens almost instantaneously as long as the UV source is present. This rapid emission distinguishes fluorescence from phosphorescence, which involves a delayed glow that continues even after the light source is removed. Phosphorescent materials store energy longer before releasing it.
What Makes Neon Colors Special?
Neon colors stand out due to their ability to fluoresce effectively, a characteristic attributed to the specialized fluorescent dyes or pigments used in their creation. Unlike conventional colors that only reflect light, fluorescent colors also absorb invisible UV light and convert it into additional visible light. This dual action of reflecting visible light and converting UV light enhances their perceived brightness.
These fluorescent dyes are engineered at a molecular level to be efficient at absorbing UV radiation and re-emitting it within the visible spectrum. This process means that neon-colored materials can appear to emit more light than they receive from the visible spectrum alone, making them vivid. The combination of reflected visible light and newly emitted visible light results in the brightness associated with these hues.
Fluorescent Materials and Observation Tips
Beyond neon colors, many other common materials exhibit fluorescence under a black light. Certain laundry detergents, for instance, contain optical brighteners that absorb UV light and emit blue light, making white clothing appear brighter. Specific minerals like fluorite and calcite, some natural substances, and security features on currency fluoresce. Highlighter inks as they contain fluorescent dyes that react strongly to UV light.
To best observe these fluorescent effects, using a black light in a darkened room is advisable, as ambient visible light can diminish the glow. While black lights primarily emit UV-A, prolonged or direct exposure to the UV source should be avoided. Looking directly into the light can cause eye strain, and extended skin exposure may lead to irritation. Using UV-protective glasses and limiting exposure duration are simple safety measures.