Ultraviolet Light and Black Light: a beginner's guide
by David Rudd Cycleback

1) Introduction

2) What is ultraviolet light?

3) The different kinds of UV light

4) Your tool for this guide: a black light

5) Where does ultraviolet light come from? How was it discovered? Why can't we see it?

6) How are black lights made?

7) Practical and interesting uses for your black light

8) Examining art and collectibles: Introduction

9) Identifying modern fakes of antique paper memorabilia

10) Identifying counterfeit US currency

11) Identifying alterations to art, collectibles

12) Examining cloth

13) Examining art glass

14) Making glow in the dark art and crafts

15) Protecting yourself from the Sun's UV

16) UV light in science and


Where does Ultraviolet Light Come From?

For humans, the common natural source of UV light is the sun. The sun gives off UVA, UVB and UVC light. UVC doesn't reach us on the earth's surface, as it is blocked by the earth's atmosphere. This is good, as UVC exposure is dangerous to human and other animals. UVA, the light we use in this book, is the safest. UVB is what causes us to tan.

Distant suns and planets give off UV light, some which makes it to earth's, and much which is blocked by our atmosphere.

Humans manufacture UVA, UVB and UVC light for industrial, commercial and scientific purposes. The human made UV products include the black lights used in this book, suntan lamps, germicidal lamps used to sterilize and currency counterfeit detectors. Even the normal office and home lights give off some UV light.


How Was UV light discovered?

Ultraviolet light has existed since long before humans were around. It wasn't invented by a human. but discovered. Ultraviolet light was discovered in 1801 by scientist Johan Wilhelm Ritter, a year after William Hershel discovered infrared light. These were the first times light invisible to human eyes were discovered.

After hearing that Hershel discovered a form of light beyond the color red, Rittner experimented to see if invisible light also existed beyond the color violet. He discovered that silver chloride turned black under ultraviolet light. Silver chloride is used in much photography, as it turns dark under sunlight. Using a prism, he spread apart light into its color spectrum, and saw that an invisible light beyond the visible violet turned black the silver chloride. This showed that an invisible form of light existed beyond the violet end of the spectrum.



Why can't we see ultraviolet?

Because we can't.

Whether eyes, ears or human-made machine, all measuring devises have limits to what they can detect and measure. The rods and cones of the human eyeballscan only detect certain wavelengths of light-- the wavelengths that fall within the visible light range. Human eyes phyisically can't detect ultraviolet, infrared, gamma and X-rays.

Just as some animals can hear sounds humans can't hear, some animals can see light we can't see. Snakes can detect infrared light, while bees, geese and butterflies can see ultraviolet. Owls can detect lower levels of light than humans, and are able to see things in the darkness of light that are invisible to us.

There are other physical limits to human sight. We can't make out detail that is too small or far away. We use optical aids like binoculars and microscopes to aid our sight. We can't see or see clearly objects that move too fast. A hand waved by our eyes looks blurred. A speeding bullet is invisible. Sight variations exist amongst humans. Some humans can see more colors than others, are able detect light at lower levels and make out details others can't. As humans get older, their night vision usually gets worse.

Though you can't see it, you can physically detect ultraviolet and infrared light. Infrared light can be hot and ultraviolet light can give you a suntan.




How Does Black Light Make Things Fluoresce?

The fluorescence, or visible light that is emitted from a material when black light is shined on it, happens at the atomic level. When you are shining a black light on an object, you are actually testing its atomic makeup!

Just as with light, heat and x-rays, black light is a form of energy. When black light is shined on a material, whether the material is glass, plastic or paper, energy is being added to the atoms of the material. The atoms can only hold this extra energy for a short amount of time before having to give it off. The atoms give off the energy in a different form than received. The atoms receive the energy as black light, but may give the energy off as heat, ultraviolet light, infrared light, visible light or, often, a combination of these. What form(s) of energy the atoms gives off is dependant on the makeup of the atoms.

If visible light is emitted by the atoms, that is the fluorescence we see. The color of this visible light is also dependant on the atomic make up. If the atom gives off just heat, ultraviolet light or infrared light, there will be no fluorescence. In a darkened room this material will remain dark.

Phosophorescence : After glow

Phospheresnce is closely related to flouroescence. Like fluorescent materials, phosphorsecant materials give off visible light when excited by energy like UV light. However, while flouroesce material quits emitting light when UV light is turned off, phosophorescant material continues to give off light. The extra duration varies from phosphorescent material to phospheresant material. Sometimes phosopherescant material gives off light for a fraction of a second longer, other material for hours or even days. The phosophorescance can be caused by UV light, but also visible light, X-rays, infrared and other light. As with fluorescence, the color, brightness and duration of the phosphorescence is caused by the atomic make up of the material.

As with fluorescent material, the added energy of UV or other light excites the atoms in phosphorescent material, raising the electorons to a higher orbital. While the electons move back to their normal orbital right away with flouroscent material, it takes longer with phosphorescent material. Thus the phosphorescent glow lasts longer.


Next: How are black lights made?

(c) david rudd cycleback, all rights reserved