What is Black
Light?
A FishTackler® article
copyright 2003 By Lynn Mills all rights reserved
Ultra-Violet, UV and black light are
all terms for the same thing. UV light is very useful in a wide array
of applications. To understand why we first need to know what UV is.
The light we see is called the visible light spectrum and includes all
the colors we can see. Our eyes detect light that falls within this
spectrum. The higher energy blues are at the top of the spectrum while
the lower energy reds occupy the bottom. Both the blue and red parts of
the spectrum go far beyond what we are able to see with our eyes. In
other words blue or more precisely violet is the highest frequency of
light that we are capable of seeing and conversely red is the lowest
frequency of light that we are able to see. Infrared, which has a
frequency range too low for us to see, has a wave length about the
length of the period at the end of this sentence, ranging down to the
size of a single cell. UV on the other hand has a wave length ranging
from a small single cell down to the size of a single protein molecule.
UV exists above the frequencies that we are able to see while
infrared falls below our visible range.
The energy of a single unit of UV light, called a photon, is
as much as 2000 times greater than that of a photon produced from
infrared. This high powered energy of the UV proton of light allows it
to excite electrons, in some substances, which causes the electrons to
jump up into a higher orbit. As the electrons falls back to its stable
orbit, a photon of light is released and this is what we see as UV
fluorescence. The colors sent back by the fluorescing substances are
usually, reds, oranges, blues and greens. However, you can trick the
eyes into seeing different colors by mixing the fluorescing colors.
Most things don't fluoresce and no visible light comes back to the
viewer. This fact makes things that do fluoresce show up like a neon
light against a stark black background of non glowing items.
| The UV light from the flashlight falls in
the lower less energetic part of the UV spectrum. Much of the UV from
our sun comes from the higher end of the UV spectrum. |
Editors
note: The UV light
mentioned in this article is no longer available. If you are interested
in making your own UV light click here. Make a
black light flashlight.
|
The
energy of these photons can damage eyes and sun burn skin not to
mention damage to the paint on our cars, or to draperies and
curtains. Even though the UV from the Black Light Flashlight is
lower energy UV, CAUTION, should still be exercised. Keep the
light away from children and never look into the light and never allow
anyone else to look directly into the light. The light you see coming
from the UV Flashlight is only 10% of the light being produced. The
other 90% is invisible, so that means these lights are very bright and
any bright light can be harmful if mistreated.
The many
Uses of Ultra-Violet light.
For most people
their first exposure to Ultra-Violet, UV, is seen as red. Red eyes and
red sun burn to be exact. You can also receive a bad UV burn from being
too close to the light source of an arc welder. Both the Sun and the
arc welder produce large quantities of high energy UV which damages the
skin and the tiny blood capillaries which is what we know as sun burn.
Most of us are also familiar with the brilliant colors produced by the
low energy black lights used on stage and in spook alleys. For us
anemic looking Caucasians tanning salons use UV lights to give us that
rich looking tan.
Crime
detection.
UV light has
become an invaluable tool in the science of forensics. Ultra violet
light helps archeologists solve many of histories mysteries. Police use
UV to find blood stains. Using a substance called Luminal police are
able to find blood traces even after a site has been cleaned of all
visible traces of blood. Semen can also be detected in much the same
way. Counterfeit money, credit cards and documents can also often be
detected using UV. Trace powders that fluoresce brightly under Ultra
violet light tell police if certain items have been handled by a
suspect.
Landlords
Use a black
light to find pet urine stains on carpets which may or may not
have been there before the occupants moved in. In either case it gives
the landlord an excuse for not returning the cleaning deposit. So it
would be a good idea to do your own check before you move in.
Movie, Stage
and Spook Alley's
Because black light
produces such striking contrasts and brilliance in color it is a very
popular medium for stage and spook alleys and to a lesser extent in
movie production. Many of the titles and credits were illuminated with
black light to give them a high contrast before computers took over the
job of creating the credits. Often times black light is used on stage
with other colored lights to create interesting colored shadows and
contrasts. For instance the stage can be illuminated from the right
with yellow lights and from the left with black lights. If the
background fluoresces blue under UV then every shadow cast by the
yellow lights will be fluorescent blue instead of black. This can be
very a useful tool too create or enhance a certain mood.
Scorpion
hunters
Because many
scorpions fluoresce under Ultra-Violet scorpion hunters use black
lights at night to find their prey, The scorpions have a cuticle that
glows a bright green when a UV light is directed at them. At night the
black light makes a scorpion stand out like spandex pants at a
presidential ball. If you decide to try this, just a word of caution.
Most areas that support scorpions also support night foraging rattle
snakes and rattle snakes do not fluoresce!
Fluorescence
and luminescence
Fluorescent
items glow under Ultra-Violet but stop glowing the moment the light
source is removed. Lets pause here to clarify some common terms.
1. Luminescent
or luminescence refers to cold light produced by chemical reaction..
The popular glow sticks, necklaces and bracelets are another example of
luminescence. Another example of chemical luminescence is produced
biologically by fish, plankton, fire flies, glow worms, and many
other life forms.
2. Fluorescence
is light that is produced by exciting electrons. Fluorescent paints
fluoresce when exposed to UV light. The ultra violet light energizes
the outer band electrons in the paint to jump up into a higher energy
band or orbit around the core of an atom. The electron is unable to
maintain itself for long in this higher energy orbit and it soon fall
back into it's more comfortable lower orbit and in the process it fires
out a photon of light which is what we see as fluorescence. The color
that fluoresces back at us depends on the fluorescent chemicals used in
the paint.
3. Phosphorescence is the
ability of a substance to continue giving off light after the charging
or excitation light is switched off. Glow in the dark toys are
phosphorescent. Phosphorescent items glow for a time after being
exposed to light. Zinc Sulfide is used extensively in glow in the
dark items but the glow only lasts a few minutes after the light source
is turned off. A new kid
on the block is Strontium
Aluminate. It glows brighter and for a much longer time when the
excitation light source is turned off. In fact emergency signs
directing people to stairways and exits, made of this new long glow
material, helped people to find their way out of the Trade centers
darkened halls and undoubtedly helped save many lives at the time of
the
911 disaster.
FishTackler
lures and spinners use Strontium Aluminate to attract fish to the
fishing spinners, lures and bait.
Science Fair
Exhibits.
My goal is
not to prepare your science fair project for you. My purpose is to
supply you with stimulating ideas that will give you many possible
directions to choose from to focus the message of your science fair
project. One thing you should do though is create a dark zone that
people can look into to see your UV exhibit. It will be much more
effective if it is in the dark. This may be something as simple as
a large cardboard box with peep holes.
Also you will need to
use your imagination with the suggestions to create a problem and then
find a way to apply scientific principles to solve that problem.
Some general ideas might be:
Not as they appear.
Show
how many things are not as they appear at first sight. For
instance, the plastic bottle of Robitussin® suppressant that looks brown in normal light
glows green under UV light why? Show how obvious a
persons false tooth is under black light. Or demonstrate how a piece of
quality white stationary fluoresces bright blue under UV while a piece
of ordinary cheap white scratch paper is dull purple. Experiment and
use you imagination to see if you can come up with other things that
are not as they appear.
Security.
Find
an expired credit card. Most credit card companies put a mark on
their cards that only shows under black light. This makes it harder to
counterfeit. For the same reason the treasury department puts a
fluorescent stripe down the left side of paper denominations of $5 and
up. Using a black light, in the dark, this stripe will fluoresce green.
Some products use invisible marks on their labels that can only be seen
with UV light.
Stary stary sky.
Paint
the inside of a large viewing box with black poster paint. Then
put tiny points of fluorescent white paint all over the blackened
interior walls of the box. Another good paint to use for this is glow
in the dark fabric paint that WalMart carries. You may want to put in
constellations like the big dipper. Bigger dots make brighter stars and
tiny dots make dim distant stars. Remember dim stars far outnumber
bright stars. Illuminate the insides of the box with the black light
flashlight. If your scene is dark, you will be amazed at how real the
stars look. To some people the stars even appear to blink. Make one
side of the box an access port. After painting the stars place well crinkled aluminum foil
where indicated in the drawing. This will defuse the black light and
distribute it more evenly. Mount the black light next to a small hole
in the side of the box so you can easily turn on or turn off the black
light. A good set of quality alkaline batteries should last several
hours with continuous use. For even greater effect stars can also be
painted on the sides and bottom of the box. Experiment with the
placement of the black light and foil to get optimum results.
|
Editors
update: For better results you may want to
substitute a 7 watt, (ideal), 120V or even a 15 watt, 120 volt,
fluorescent black light. The 15 watt bulb and fixture should be
available at most WalMart, Low's, Home Depot or Home
Base stores. You may have to go online to find the 7 watt 120 volt
black light and fixture.
|
Spoiled Food
Health
inspectors use Ultra-Violet. It might be interesting to let
several kinds of food sit out and spoil while keeping some fresh in the
refrigerator. Place samples of the fresh food and the spoiled
food together under the black light. I have not tried this but areas
where there are bacteria colonies should show up under UV. You may
find people turning their noses up at you project if you use spoiled
food in your display. You could seal it in plastic bags to keep odors
trapped or if you have a digital cameras you might use pictures
instead. Digital cameras are very sensitive to UV light. You will need
to take the pictures without using the flash as the flash will wash out
the UV effect.
.
These are just a few
ways you can use black light. There are many more. Perhaps you
can come up with novel new uses. Good luck and have fun with your black
light. If you have more uses for black light or other projects email
me. I would love to hear from you. Email Lynn: wwindmills@att.net
Robitussin® is a trademark owned by AMERICAN
HOME PRODUCTS CORPORATION
Some
of my other pages