black light

A Black light or UV Light is a lamp emitting electromagnetic radiation that is almost exclusively in the soft near ultraviolet range, and emits very little visible light. The black light was invented by William H. Byler, in 1935.[citation needed]

In medical use, such a light source is referred to as a Wood's lamp.
Fluorescent black lights are typically made in the same fashion as normal fluorescent lights except that only one phosphor is used and the normally clear glass envelope of the bulb may be replaced by a deep-bluish-purple glass called Wood's glass, a nickel-oxide–doped glass, which blocks almost all visible light above 400 nanometers. In practice, partly due to cost but mainly because Wood's glass does not make a satisfactory material for lamp manufacture, the lamp will be made from normal glass and a relatively thin coating of a UV filtering material is applied to the exterior. The color of such lamps is often referred to in the trade as "blacklight blue" or "BLB." This is to distinguish these lamps from "bug zapper" blacklight ("BL") lamps that don't have the filter material

The phosphor typically used for a near 368 to 371 nanometer emission peak is either europium-doped strontium fluoroborate (SrB4O7F:Eu2+) or europium-doped strontium borate (SrB4O7:Eu2+) while the phosphor used to produce a peak around 350 to 353 nanometers is lead-doped barium silicate (BaSi2O5:Pb+). "Blacklight Blue" lamps peak at 365 nm.

European Black Light, UV-A, UV-B and Actinic Tubes possess different numbering systems to identify them, Philips use one system which seems to be falling into obsolescence, (German) Osram's system seems to be dominating throughout the world outside North America. The table below for details.
Phosphor Peak, nm Width, nm Philips Suffix. Osram Suffix. U.S. Type Uses
Mixture 450 50 - /71 - hyperbilirubinaemia, polymerization
SrP2O7, Eu 420 30 /03 /72 - polymerization
SrB4O7, Eu 370 20 /08 /73 ("BLB") Forensics, Night Clubs
SrB4O7, Eu 370 20 - /78 ("BL") Suntanning, psoriasis, polymerization, insect attraction
BaSi2O5, Pb 350 40 /09 /79 "BL" suntanning lounges, insect attraction
BaSi2O5, Pb 350 40 /08 - "BLB" Forensics, Dermatology, Night Clubs
SrAl11O18, Ce 340 30 - - - photochemical uses
MgSrAl10O17, Ce 310 40 - - - medical applications, polymerization

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Peak Position approximated to the nearest decade.

Width between 50% intensity points on shoulders of peak.

This table lists tubes generating blue, U.V.A and U.V.B, 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 types available.

Osram wood's glass tubes seem to use a fairly narrow band emitting phosphor, Europium activated Strontium Pyroborate, with a peak at about 370nm, whereas North American and Philips Wood's glass tubes seem to use the wider band emitting, Lead activated Calcium Metasilicate, with a shorter wavelength peak at about 350nm. These two seem to be the most commonly used, and different manufacturers offer either one or the other and often both.

A black light may also be formed by simply using Wood's glass instead of clear glass as the envelope for a common incandescent bulb. This was the method used to create the very first black light sources. Though it remains a cheaper alternative to the fluorescent method, it is exceptionally inefficient at producing UV light, (less than 0.1 percent of the input power), owing to the black body nature of the incandescent light source. Incandescent UV bulbs, due to their inefficiency, may also become dangerously hot during use. Often the filament is "overburned", and run at a higher temperature to increase the proportion of U.V.A in the black-body emission, this drastically reduces the life of the lamp from a typical 1000 hours to around 100 hours.

More rarely still, high power, 125 and 400 watt mercury vapor black lamps can be found, these do not utilize the use of phosphors, but rely on the intensified and slightly broadened 365nm spectral line of Mercury from high pressure discharge at between 5 and 10 atmospheres pressure depending upon the specific type. These lamps use envelope of Wood's glass to block all the visible lines of Mercury and the short wavelength U.V.C resonance lines, which are harmful. Some other spectral lines, falling within the pass band of the Wood's glass, at 312 and 404.5nm contribute to the output. These lamps are used mainly for theatrical and concert displays and although, like the filament lamps described above they become very hot during normal use, they far more effective U.V.A producers per unit of power consumption.

Some UV fluorescent bulbs specifically designed to attract insects for use in bug zappers use the same near-UV emitting phosphor as normal blacklights, but use plain glass instead of the more expensive Wood's glass, these are listed in the table above. Plain glass blocks less of the visible mercury emission spectrum, making them appear light blue-violet to the naked eye. These lamps are referred to as "blacklight" or "BL" in most North American lighting catalogs. European equivalents are the Philips TL-XXW/09, emitting a peak at 350nm, and the Osram LXXW/78, emitting a peak at 371nm, among others.

Ultraviolet light can be also generated by some light-emitting diodes, but wavelengths below 380nm are uncommon and the emission peaks are broad.