Use of UV ray in identification of counterfeit currency:
i) If the note is counterfeit, the entire fill lights up brightly under the UV light. A high—end counterfeit detection light will give an audible warning sound when it detects a counterfeit bill.
ii) Anti counterfeit indicator become illuminated if the currency is authentic. One will see a bright, fluorescent, security strip on the left side of the bill. The $ 5 note glows blue, the $ 10 dollar note glows orange, the $ 20 glows green. These colors can only, seen under UV light.
iii) The watermark on a real note will not be visible under the UN’ light, while counterfeit currency may show a poorly printed watermark.
iv) For preventing counterfeit, some sign remain invisible in real note. Which is visible only after absorbing ultraviolet ray. There is no sign for counterfeit currency.
v) Security thread of different bright colours is seen under UV ray. But fake currency has no bright colors of security thread.
Wavelength of ultraviolet ray is 2 – 400 nm.
Recently an important use of quantitative analysis is to identify the fake currency or passport. UV ray can be used in this purpose.