Most of us are aware of fluorescent lights that glow at night absorbing the energy directed towards it. Black light bulb is much similar to fluorescent light and works on the same principle.
A black light bulb consists of a dark coloured glass coated with phosphor in activated form, two electrodes and mercury in small amounts. Energy is produced by electrodes which vaporises mercury present. This energy is absorbed by the phosphor coat the is present in the bulb giving light rays, the thick blue glass of the bulb absorbs almost all light and passes only ultraviolet rays outside it. Thus we get the black lights that give an insignificant glow at night. the bulb is more widely used to find fakes, especially fake money.
Human eye can see in light that comes under the VIBYOR. These colours which are from violet to red bring about different colours too which are in visibility range. When all these colours combine to form black, the visibility to unaided human eye is restricted. Black light bulb thus produces light that is not visible to human eye, but the commercial bulbs produced have a small glow that shows us its presence due to the phosphor present in it. It is used largely in stage shows where lighting is required to give different effect and moods, also it is used in hotels and disco clubs that require different colour tones to give lively look.
The most important use of black light bulb is in the detecting counterfeit money. This is done by placing the money on the bulb, the ink that is used to print money differ from normal ink. These prints are not visible in normal light but when passed along a black light bulb the printed words or symbols can be easily seen. This differentiates between original and fake money.
Another use of this, is in the finger print attendance registry. Mostly used in fields where large numbers of employees are employed, like that of parks or large factories, the thumb impression is used as identity and the attendance is taken using this. This gives a foolproof method to register attendance, especially in large concerns people find it easy to take unaccounted leave, this is widely restricted by the usage of black light bulb aided thumb printer. Some prisons use this method for visitor’s identification.
The ID given to visitors have stamp that is printed with ink that is visible in black light bulb, and hence checking and having control of the visitors is possible in these prisons. Since there is no evidence of the light produced like heat or light the visitor is normally unaware of the presence of a vigilance method with him. In cleaning companies too it is used to find remains of urine that is not properly cleaned. Hence black light bulb is very useful in day to day life of man. The presence of which is sometimes not noticed.
While buying a black light bulb one should take enough care to learn about its capacity and average life, which would give a proper worth for the money spent on it.
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