The Chemistry of Black Lights

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Introduction
Black Lights are lights that use long-wave or ultraviolet light, also known as UV rays.  I chose the Chemistry of Black lights because I’ve always wondered how they worked and if we humans can’t see UV rays, how come we see light from a Black light?  Black lights don’t really have an effect on my life, except for when I’m around one for too long I get slightly dizzy.
Composition of ...


Black lights are basically light emissions in the ultraviolet wavelengths of the electromagnetic spectrum.  While visible light has wavelengths between 380 to 750 nanometers, ultraviolet light is shifted toward the ultraviolet end of the visible spectrum and may span between 400 to 10 nanometers.  Meaning that humans can only see a small portion of the ultraviolet light.  Most black light sources peak at 365 nanometers and use phosphor to convert energy into ultraviolet radiation.  Usually black light sources can be found in the form of fluorescent tubes.  Ordinary fluorescent tubes operate by discharging an electrical current between two metal filaments inside an inert gas, most likely containing a little amount of mercury vapor.  The mercury atoms convert part of the energy into light.  Since ultraviolet light is invisible to the human eye, the phosphor coatings are used to change it into light humans can see.  The special phosphor coatings are used to filter out the harmful ultraviolet B and C wavelengths, and only allowing ultraviolet wavelengths that are not harmful to the human eye through.


Main Chemicals, Compounds, Components

A black light may seem like a futuristic invention, but actually, it is only a regular, sterile fluorescent  light.  Regular fluorescent light bulbs are tubes filled with a noble gas with some mercury gas mixed in. When energy is pumped into the mercury atoms from electricity, they emit photons, but the photons human eyes cannot see.  Mercury emits ultraviolet light, which is unhealthy and invisible, since it is more energetic than visible light.  The reason that most fluorescent light is visible, while black light is not, is because of the coating on the outside of the bulb.  The bulb is coated in a hazy white substance of phosphors.  When phosphors are hit with photons they create both heat and light.  As a result of that specific combination of heat and light, the photons that the phosphors emit are just a little less active than the photons that the phosphors absorb.  The loss of energy sends the photons into the visible light range, meaning humans can now see it.  Black light bulbs have phosphor coating that absorbs the higher-end UV light, but lets the relatively harmless and low-energy UVA waves get through. Those UVA waves zoom around the room and hit other phosphors; ones that we usually don't notice. It's the phosphors sprinkled around our daily lives that make black light so cool.  

Now to explain why so many substances and objects in our daily life seem to “glow in the dark” whenever a black light is around. Fluorescent substances absorb the ultraviolet light and then re-emit it almost instantaneously. Some energy gets lost in the process, so the emitted light has a longer wavelength than the absorbed radiation, which makes this light visible and causes the material to appear to 'glow'.   Many bodily fluids glow under a blacklight because after calcium, phosphorus is the most abundant mineral found in the human body.  A major reason we don’t constantly see a glow from the world around us is because the brighter visible light drowns it out.  Which isn't to say that we don't perceive the phosphorescence. Paper is treated with phosphorus, as are white clothes and laundry detergents. These added phosphorus compounds help clothes and paper have a bright, marketable white glow.

Chemistry's Role

Our eyes can see visible light in a spectrum ranging from red through orange, yellow, green, blue and violet.  Above violet is a color we cannot see, ultraviolet light.  A black light produces a UVA light, which is not harmful compared to other lights.  

Shown is the electromagnetic spectrum.  


The uses for black lights are for many different reasons,  but mostly they are used to make certain substances or objects “glow in the dark”, such as clothing or pictures.

A “particle” of light is called a photon. It has no mass—just energy. You can think of it as a packet of energy. When this packet of energy (photon) comes into contact with an electron in the outer regions of an atom, the electron absorbs the energy and jumps to a higher energy state. It moves to a higher orbital, as physicists call it.  If it’s a photon in the UV range striking an atom, and if the atom emits a visible photon in return, the material is UV sensitive. This is the glow effect associated with black light, and you typically can’t see it unless there is complete darkness and you have an artificial light source emitting UV light. The more sensitive the material is, the brighter it glows. And the more UV light is applied, the brighter it glows still.




The main component in a black light is light itself.  Light originates as single photons, or particle/waves having no mass, and no electric charge. Photons are emitted by electrons as they lose orbital energy around their atom. The expendable orbital energy is transferred to the electron either when it is bumped by an atom or when it is struck by another photon. Before being excited to a higher electron shell, the electron is in the lowest possible shell, or ground state.  The ground state is forced by the attraction between the electron and the proton that are found in the nucleus.  When an electron is excited to a higher electron shell, it almost immediately seeks the ground state.  As the electron returns to the ground state, a frequency, or wave is emitted by the energy being displaced. To the human eye, this wave of energy is seen as light.  Shown below is an example of the electron returning to ground state and emitting a wavelength.  The reason black lights seem so different are because of the size of wavelength emitted.  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light but shorter than X-ray wavelengths.  It is named because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the color violet.  They are also indirectly visible, by causing fluorescent or neon materials to glow with visible light.

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About the Author
Emmy Reinschmidt is a junior at Billings Senior High School.  She is in Mr. Beals chemistry class and enjoys learning all about chemistry.  In her spare time she plays tennis,is an avid reader, hangs out with friends and spends time with her family.  She is planning on attending her senior year at Senior High School and then going off to college in Bozeman to become an architect and interior designer.  One of her goals is to leave an impact on the world with her new ideas and unique way of thinking.  Traveling is one of her favorite things to do and when she has enough money saved, she plans on taking a trip around the world.  Looking toward her future, Emmy is excited to experience life and is ready for whatever comes her way.
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