Blacklight in the context of "Ultraviolet light"

Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with colored visible light. The color of the light emitted depends on the chemical composition of the substance. Fluorescent materials generally cease to glow nearly immediately when the radiation source stops. This distinguishes them from the other type of light emission, phosphorescence. Phosphorescent materials continue to emit light for some time after the radiation stops.This difference in duration is a result of quantum spin effects.

Fluorescence occurs when a photon from incoming radiation is absorbed by a molecule, exciting it to a higher energy level, followed by the emission of light as the molecule returns to a lower energy state. The emitted light may have a longer wavelength and, therefore, a lower photon energy than the absorbed radiation. For example, the absorbed radiation could be in the ultraviolet region of the electromagnetic spectrum (invisible to the human eye), while the emitted light is in the visible region. This gives the fluorescent substance a distinct color, best seen when exposed to UV light, making it appear to glow in the dark. However, any light with a shorter wavelength may cause a material to fluoresce at a longer wavelength. Fluorescent materials may also be excited by certain wavelengths of visible light, which can mask the glow, yet their colors may appear bright and intensified. Other fluorescent materials emit their light in the infrared or even the ultraviolet regions of the spectrum.

A head shop is a store that sells drug-related paraphernalia. They emerged from the hippie counterculture in the late 1960s, and at that time, many of them had close ties to the anti-Vietnam War movement as well as groups in the marijuana legalization movement like LeMar, Amorphia, and the National Organization for the Reform of Marijuana Laws.

Products sold may include magazines (e.g., about cannabis culture, cannabis cultivation, tattooing, and music), clothing, and home décor (e.g., posters and wall hangings illustrating drug culture themes such as cannabis, jam bands like The Grateful Dead, Phish, psychedelic art, etc.). Some head shops also sell oddities, such as antique walking sticks and sex toys. Since the 1980s, some head shops have sold clothing related to the heavy metal or punk subculture, such as band T-shirts and cloth patches with band logos, studded wristbands, bullet belts, and leather boots. Other items offered typically include hashish pipes, "one hitter" pipes; pipe screens; bongs (also referred to as water pipes); roach clips (used for smoking the end of a marijuana "joint"); vaporizers used for inhaling THC vapor from cannabis; rolling papers; rolling machines; small weighing scales; small ziplock baggies; cannabis grinders (i.e. herb grinders); blacklight-responsive posters and blacklights; incense; cigarette lighters; "stashes", which include a range of standard consumer products such as clocks, books, tins of cleaning powder, and toilet brushes which have hidden compartments for cannabis and non-camouflaged "stash boxes" which are tins or wooden containers for storing marijuana; and legal highs such as whipped-cream chargers (which contain nitrous oxide) and Salvia divinorum (both of which are illegal in some countries and some US states for recreational purposes). Some head shops also sell items used for home cultivation of marijuana plants, such as hydroponic equipment and lights and guidebooks on cultivation. Since the 2000s, some head shops also sell e-cigarettes and the flavoured liquids used with these devices.