blacklight blacklight a blacklight, also called a uv-a light, wood's lamp, or ultraviolet light, is a lamp that emits long-wave (uv-a) ultraviolet light and very little visible light. one type of lamp has a violet filter material, either on the bulb or in a separate glass filter in the lamp housing, which blocks most visible light and allows through uv, so the lamp has a dim violet glow when operating. blacklight lamps which have this filter have a lighting industry designation that includes the letters "blb". this stands for "blacklight blue". a second type of lamp produces ultraviolet but does not have the filter material, so it produces more visible light and has a blue color when operating. these tubes are made for use in "bug zapper" insect traps, and are identified by the industry designation "bl". this stands for "blacklight". black light fluorescent tubes. the violet glow of a black light is not the uv light itself, but visible light that escapes being filtered out by the filter material in the glass envelope. blacklight sources may be specially designed fluorescent lamps, mercury-vapor lamps, light-emitting diodes (leds), lasers, or incandescent lamps. in medicine, forensics, and some other scientific fields, such a light source is referred to as a wood's lamp, named after robert williams wood, who invented the original wood's glass uv filters. although many other types of lamp emit ultraviolet light with visible light, black lights are essential when uv-a light without visible light is needed, particularly in observing fluorescence, the colored glow that many substances emit when exposed to uv. black lights are employed for decorative and artistic lighting effects, diagnostic and therapeutic uses in medicine, the detection of substances tagged with fluorescent dyes, rock-hunting, scorpion-hunting, the detection of counterfeit money, the curing of plastic resins, attracting insects and the detection of refrigerant leaks affecting refrigerators and air conditioning systems. strong sources of long-wave ultraviolet light are used in tanning beds. uv-a presents a potential hazard when eyes and skin are exposed, especially to high power sources. according to the world health organization, uv-a is responsible for the initial tanning of skin and it contributes to skin ageing and wrinkling. uv-a may also contribute to the progression of skin cancers. additionally, uv-a can have negative effects on eyes in both the short-term and long-term. types fluorescent two black light fluorescent tubes, showing use. the top is a f15t8/blb 18-inch, 15-watt tube, used in a standard plug-in fluorescent fixture. the bottom is an f8t5/blb 12-inch, 8-watt tube, used in a portable battery-powered black light sold as a pet urine detector. fluorescent black light tubes are typically made in the same fashion as normal fluorescent tubes except that a phosphor that emits uva light instead of visible white light is used on the inside of the tube. the type most commonly used for black lights, designated blacklight blue or "blb" by the industry, has a dark blue filter coating on the tube, which filters out most visible light, so that fluorescence effects can be observed. these tubes have a dim violet glow when operating. they should not be confused with "blacklight" or "bl" tubes, which have no filter coating, and have a brighter blue color. these are made for use in "bug zapper" insect traps where the emission of visible light does not interfere with the performance of the product. the phosphor typically used for a near 368 to 371 nanometer emission peak is either europium-doped strontium fluoroborate (srb2f8:eu2+) or europium-doped strontium borate (sr3b2o6:eu2+) while the phosphor used to produce a peak around 350 to 353 nanometres is lead-doped barium silicate (basi2o5:pb+). "blacklight blue" lamps peak at 365 nm. compact fluorescent (cf) black light bulb manufacturers use different numbering systems for black light tubes. philips uses one system which is becoming outdated (2010), while the (german) osram system is becoming dominant outside north america. the following table lists the tubes generating blue, uva and uvb, in order of decreasing wavelength of the most intense peak. approximate phosphor compositions, major manufacturer's type numbers and some uses are given as an overview of the types available. "peak" position is approximated to the nearest 10 nm. "width" is the measure between points on the shoulders of the peak that represent 50% intensity. various phosphor compositions used in blacklight phosphormixture peak(nm) width(nm) philipssuffix osramsuffix u.s. type typical use — 450 50 — /71 — hyperbilirubinaemia, polymerization srp2o7:eu 420 30 /03 /72 — photochemical polymerization srb4o7:eu 370 20 /08 /73 ("blb") forensics, lapidary, night clubs srb4o7:eu 370 20 — /78 ("by") insect attraction, polymerization, psoriasis, tanning beds basi2o5:pb 350 40 /09 /79 "bl" insect attraction, tanning beds basi2o5:pb 350 40 /08 — "blb" dermatology, lapidary, forensics, night clubs sral11o18:ce 340 30 — — — photochemistry mgsral10o17:ce 310 40 — — — medical applications, polymerization spectrum of a black light fluorescent tube. fwhm spectral bandwidth of the 370 nm peak is about 20 nm. the tiny secondary peak (2) is light from the mercury vapor line at 404 nm leaking through the filter, which gives the lamp its purple glow. "bug zapper" tubes another class of uv fluorescent bulb is designed for use in "bug zapper" flying insect traps. insects are attracted to the uv light, which they are able to see, and are then electrocuted by the device. these bulbs use the same uv-a emitting phosphor blend as the filtered blacklight, but since they do not need to suppress visible light output, they do not use a purple filter material in the bulb. plain glass blocks out less of the visible mercury emission spectrum, making them appear light blue-violet to the naked eye. these lamps are referred to by the designation "blacklight" or "bl" in some north american lighting catalogs. these types are not suitable for applications which require the low visible light output of "blb" tubes lamps. incandescent 100-watt incandescent black light bulb a black light may also be formed by simply using a uv filter coating such as wood's glass on the envelope of a common incandescent bulb. this was the method that was used to create the very first black light sources. although incandescent black light bulbs are a cheaper alternative to fluorescent tubes, they are exceptionally inefficient at producing uv light since most of the light emitted by the filament is visible light which must be blocked. due to its black body spectrum, an incandescent light radiates less than 0.1% of its energy as uv light. incandescent uv bulbs, due to the necessary absorption of the visible light, become very hot during use. this heat is, in fact, encouraged in such bulbs, since a hotter filament increases the proportion of uva in the black-body radiation emitted. this high running-temperature drastically reduces the life of the lamp, however, from a typical 1,000 hours to around 100 hours. mercury vapor a 160-watt mercury vapor black light high power mercury vapor black light lamps are made in power ratings of 100 to 1,000 watts. these do not use phosphors, but rely on the intensified and slightly broadened 350–375 nm spectral line of mercury from high pressure discharge at between 5 and 10 standard atmospheres (500 and 1,000 kpa), depending upon the specific type. these lamps use envelopes of wood's glass or similar optical filter coatings to block out all the visible light and also the short wavelength (uvc) lines of mercury at 184.4 and 253.7 nm, which are harmful to the eyes and skin. a few other spectral lines, falling within the pass band of the wood's glass between 300 and 400 nm, contribute to the output. these lamps are used mainly for theatrical purposes and concert displays. they are more efficient uva producers per unit of power consumption than fluorescent tubes. led uv led ultraviolet light can be generated by some light-emitting diodes, but wavelengths shorter than 380 nm are uncommon, and the emission peaks are broad, so only the very lowest energy uv photons are emitted, within predominant not visible light. safety although black lights produce light in the uv range, their spectrum is mostly confined to the longwave uva region, that is, uv radiation nearest in wavelength to visible light, with low frequency and therefore relatively low energy. while low, there is still some power of a conventional black light in the uvb range. uva is the safest of the three spectra of uv light, although high exposure to uva has been linked to the development of skin cancer in humans. the relatively low energy of uva light does not cause sunburn. uva is capable of causing damage to collagen fibers, however, so it does have the potential to accelerate skin aging and cause wrinkles. uva can also destroy vitamin a in the skin. uva light has been shown to cause dna damage, but not directly, like uvb and uvc. due to its longer wavelength, it is absorbed less and reaches deeper into skin layers, where it produces reactive chemical intermediates such as hydroxyl and oxygen radicals, which in turn can damage dna and result in a risk of melanoma. the weak output of black lights, however, is not considered sufficient to cause dna damage or cellular mutations in the way that direct summer sunlight can, although there are reports that overexposure to the type of uv radiation used for creating artificial suntans on sunbeds can cause dna damage, photoaging (damage to the skin from prolonged exposure to sunlight), toughening of the skin, suppression of the immune system, cataract formation and skin cancer. uv-a can have negative effects on eyes in both the short-term and long-term. uses ultraviolet radiation is invisible to the human eye, but illuminating certain materials with uv radiation causes the emission of visible light, causing these substances to glow with various colors. this is called fluorescence, and has many practical uses. black lights are required to observe fluorescence, since other types of ultraviolet lamps emit visible light which drowns out the dim fluorescent glow. medical applications a wood's lamp is a diagnostic tool used in dermatology by which ultraviolet light is shone (at a wavelength of approximately 365 nanometers) onto the skin of the patient; a technician then observes any subsequent fluorescence. for example, porphyrins—associated with some skin diseases—will fluoresce pink. though the technique for producing a source of ultraviolet light was devised by robert williams wood in 1903 using "wood's glass", it was in 1925 that the technique was used in dermatology by margarot and deveze for the detection of fungal infection of hair. it has many uses, both in distinguishing fluorescent conditions from other conditions and in locating the precise boundaries of the condition. fungal and bacterial infections it is also helpful in diagnosing: fungal infections. some forms of tinea, such as trichophyton tonsurans, do not fluoresce. bacterial infections corynebacterium minutissimum is coral red pseudomonas is yellow-green cutibacterium acnes, a bacterium involved in acne causation, exhibits an orange glow under a wood's lamp. ethylene glycol poisoning fluorescein glowing under ultraviolet light a wood's lamp may be used to rapidly assess whether an individual is suffering from ethylene glycol poisoning as a consequence of antifreeze ingestion. manufacturers of ethylene glycol-containing antifreezes commonly add fluorescein, which causes the patient's urine to fluoresce under wood's lamp. other wood's lamp is useful in diagnosing conditions such as tuberous sclerosis and erythrasma (caused by corynebacterium minutissimum, see above). additionally, detection of porphyria cutanea tarda can sometimes be made when urine turns pink upon illumination with wood's lamp. wood's lamps have also been used to differentiate hypopigmentation from depigmentation such as with vitiligo. a vitiligo patient's skin will appear yellow-green or blue under the wood's lamp. its use in detecting melanoma has been reported.