UV Light Question

I understand the physics of UV lights, but what is the difference between a long wave UV light (about $20) and a short wave UV light (about $50+++)as they relate to collecting US tagged stamps?

The chemical make up of the bulbs gives you the ranges of light
SrP2O7,Eu = nm 420 which is polymerization and a chemical mixture that gives you nm 450 is hyperbilirubinemia,where as MgSrAl10O17,Ce nm 310 is for medical applications,the ranges of nm 450 and nm 310 are longwave UV spectrum ranges.

Oh well now that clears it all up.

To tan or not to tan that is the question I ask of thee.

Seriously though.
UV light is divided, at a minimum, into both Shortwave and Longwave radiation. Shortwave UV is produced by low pressure mercury arcs, with a wavelength of 254 nanometers, while Longwave, produced by low to high pressure mercury arcs, has a wavelength of from 320 to 400 nanometers. A nanometer is a unit of length used to define wavelengths of energies in the electromagnetic spectrum, equaling one millionth of a millimeter.

While Longwave UV, sometimes referred to as "blacklight", is safe, Shortwave UV can irritate the eyes and burn the skin, so exposure should be controlled and ideally, UV goggles should be worn to prevent eye damage from inadvertently looking at the light source.

Shortwave, clear bulb and burns. Longwave, colored bulb.

For detecting tagging on US stamps, you MUST use the short wavelength UV lamp. The long wavelength lamp will only detect the tagging on a very small handful of US stamps, and the tagging contrast will not be very strong. On the other hand, tagging will clearly photoluminesce (green, orange, or bright whitish -- depending on the stamp) with the short wavelength UV.

For US stamps, the primary function of the long wavelength UV lamp is to detect paper varieties and also detecting some types of altered stamps or stamps with hidden damage.

I use a research grade dual wavelength filtered UV lamp that operates at 254nm and 365nm. It's pretty powerful and allows me to light up a whole pane of stamps; however, it is overkill for philatelic purposes.

The statements above apply to most (including Canada), but not all countries. I've yet to find a UV lamp that is suitable for easy detection of tagging on the experimental phosphor issues of GB. While the phosphor can usually be detected by just holding the stamp at an angle under a light, there are a couple of issues where the vertical background color bands match well with the phosphor bands and makes it difficult to find the phosphor. On those issues, I often try to get them with selvage, as the tagging bands can be seen on the white selvage.

Remember, never look into the UV lamp directly and minimize extended exposure to your skin. ESPECIALLY if you are using the short wavelength lamps. The philatelic-grade lamps are usually low wattage, so you are very unlikely to run into health problems -- but better safe than sorry and it's good to practice safety.

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By Homer - I think I've got it! The part I didn't know was that you can't see US tagging using the long wavelength light. Thank you all!

Sorry mate I did try to be to technical
also I had to rush as my wife was waiting for me to take her to work.