Intro: Make STEM Fun With UV LEDs
Everyone from from the youngest child to the oldest senior citizen is fascinated by black lights. The same UV light most people associate with the 1960s and 70s hippy scene is also one of the most versatile and fun scientific tools available today. What child or adult wouldn't enjoy exploring their world in whole a new light?
Step 1: A Word About UV Safety.
The term "Ultraviolet" is a bit misleading when used to describe LEDs. UV LEDs actually emit a very narrow band of long wave, "near ultraviolet" light at approximately 390 to 400 nm. This wavelength falls within the same, much broader band as regular fluorescent black lights. This means that UV LEDs will NOT make you go blind even if you stare directly at them for hours at a time. Neither will they kill bacteria. They will not give you skin cancer either. UV LEDs are completely safe no matter what you have heard or read elsewhere on the internet.
The blinding, killing and cancer causing high energy short wave UV radiation falls in the 10 to 315 nm range. This danger zone of UV light is also completely invisible to the human eye.
Step 2: Categories
Here are just a few of the areas of science UV LEDs can be used in.
- Aseptic Technique
- Food Safety
- Atmospheric Science
- Just for Fun
Step 3: What You Need
- UV LEDs
- 3 volt lithium batteries (Types 3032, 2032, 2012 and 2430 all work great)
Total Cost = around $0.37 per student
Step 4: A Look Inside
Begin by studying LEDs, how they are made, why they work, etc...
Step 5: Electricity
- Students can learn the difference between conductors and insulators.
- They can experiment using a pencil mark on paper as a variable resistor to dim and brighten the LED.
- Aluminum foil can be used to fashion a simple switch.
Step 6: Electronics
- The fact that LEDs only light when the battery polarity is correct can lead to a discussion of semiconductor properties.
- Discussions about various types of batteries and how they provide a voltage potential.
- What are resistors and what do they do in a circuit?
- What is the difference between a cathode and an anode?
- Calculate how long a battery can operate an LED.
Step 7: Physics
Some lesson examples are:
- Why do LEDs emit light but regular diodes do not?
- Why do some objects glow under UV light?
- Why do some objects emit a different color light when exposed to UV light than under white light? For example, yellow highlighters emit green light when exposed to UV light. Olive oil which is normally slightly greenish brown emits reddish orange light when exposed to UV light?
- Why do some objects continue to glow even after the UV light is turned off?
Step 8: Epidemiology
We hear the words epidemic and pandemic often, but few people truly understand how an infectious agent spreads. A UV LED and a product called Glow Germ® provides an excellent demonstration of how a virus could rapidly spread through a population of people. A hand "infected" with Glow Germ is shown below under UV light.
Simply place an object in the classroom that has been "infected" with Glow Germ. Choose an object that the students are sure to touch like an ink pen covered in invisible "germ powder" that is used to "sign in" on a roster sheet or something several students would touch and spread to others. I would suggest practicing with whatever object you choose to make sure it works well. An explanation of infectious agents and how they are spread could be followed by an mock epidemiology investigation using UV LEDs to determine which students have been infected. To make it even more interesting, the infecting agent could be secretly removed from or hidden in the classroom and interviews could be conducted to try to determine where the infection originated in the classroom.
Step 9: Mathematics
- Calculate the current through the LED using OHM's law
- Use OHM's law to calculate the resistance necessary to light the LED at various voltages. e.g 3, 5, 9, 12 and 24 volts DC.
- Calculate the internal resistance of the LED by measuring the current flowing through and the voltage drop across the LED.
Step 10: Chemistry
UV LEDs can also be used for more advanced projects like studying the effectiveness of sun screens and sun blocks. Glass microscope slides or plastic bags covered with these products can be used with UV LEDs to measure the amount of UV light each allows to pass. A fluorescent substance behind the slide or inside the plastic bag can offer a rough estimate of how much UV light each substance blocks.
The following web site has instructions on how to make fluorescence which is highly fluorscent in UV light. http://woelen.homescience.net/science/chem/exps/fluorescence/index.html
Step 11: Biology
In Biology UV LEDs can be used for all sorts of things.
Picture 1 - These are lichens on a tree in my back yard. The UV light revealed two types. One emits a pink color and the other emits a deep blue. Both types look identical in normal light.
Picture 2 - While wandering around the garden with a UV flashlight at night I discovered that the pollen in this bloom emitted bright red light. An internet search revealed that some insects, birds, and mammals can actually see in the UV spectrum. It would be interesting to see which insects are attracted to this bloom.
Picture 3 - This is a head of ornamental cabbage in my wife's flower bed. Only the top center of the plant fluoresces.
Picture 4 - This is a picture of a zebra fish embryo that has ingested red fluorescent tagged cholesterol. The embryo being clear it makes it easy to see where the cholesterol accumulates.
Step 12: Forensics
- Picture 1 - UV light can be used to detect counterfeit money. The paper money is printed on does not fluoresce like normal paper. (see picture 1). American currency printed since 2004 has a plastic strip integrated into the paper that glows under UV light. The strips glow blue in $5 bills, orange in $10 bills, green in $20 bills, yellow in $50, and red in $100 bills. Because the strip is only visible under UV light, it is nearly impossible to duplicate using even the most advanced color copiers. The color variations also help to prevent currency bleaching, in which small denomination bills are bleached and reprinted to resemble higher denominations.
- Picture 2 - In 1950 paper manufacturers started adding UV dyes to white paper to make it appear brighter like UV dyes in laundry detergent makes your clothes look brighter. This makes it very easy to detect document forgeries since pre-1950 documents do not glow under UV light as post-1950 documents do. This also helps to identify forged currency since most all of it is printed on modern paper that glows under UV light. The sheet of paper in the middle is pre 1950. The other two are post 1950.
- Picture 3 - Many bank notes like the one from Visa pictured below have special UV inks to help prevent fraud.
Step 13: Food Safety
Ever wonder if there are rats or mice roaming the kitchen when the lights are out. Food safety inspectors want to know the same thing. Luckly rodent urine and hair fluorses under UV light so detecting the presence of rodents is as simple as turning off the lights and turning on your UV LED.
Rodent urine emits blue-white to yellow-white fluorescence when viewed with UV light. The fresher the stain the more blue will fluoresce. Urine stains on food bags, containers, floors, etc. are invisible in room light. However, they are readily discernible under black light. Furthermore, rodents urinate when in motion and their paths are visible under black light in characteristic “droplet” pattern or trails so with a little detective work you can track them to their entry point.
Rodents have oily hair that emits a blue-white fluorescence under UV light. The oil will leave tiny smudge marks along walls where they travel. Government food inspectors routinely use UV light to visually check for rodent hair contamination in grains.
However, use caution when investigating suspected rodent activity as some fluorescent cleaning products or their residue may splash on walls when cleaning or moping and may produce false positives during your investigation.
The picture on this page shows a rat nesting box under regular and UV light. Blue fluorescent urine stains are clearly visible under UV light.
Step 14: Zoology
- Why do some insects, birds and animals fluoresce and which ones?
- Do they fluoresce for protection or as a warning?
Step 15: UV in the Research Laboratory
UV light is very common in research laboratories. One of the most common uses is in the area of genomics research. There DNA and RNA are treated with special fluorescent chemicals that make them visible under UV light. An excellent example of this is the photograph below which shows various sized bands of DNA that have been separated in an agarose gel.
Step 16: Microbiology
UV light can be used to kill bacteria, microorganisms, molds and fungus. Here it is being used to kill bacteria on eggs. UV sterilization is often used in air and water purification systems, aquariums and ponds, laboratories and food and beverage production.
Read more about how UV light kills microorganisms at the following link:
Step 17: Atmospheric Science
UV light is one of the most effective methods of sterilization used. It will kill nearly anything. However, scientist have discovered that the stratosphere contains bacteria and fungi that live and reproduce there with no apparent adverse effect from the extreme UV light they are exposed to. How these organisms got there, how they stay alive and why the intense UV light does not destroy them is a strange story indeed. Clink the link below or do an internet search for more information.
Step 18: Automotive
Automotive antifreeze contains fluorescent dyes that glow bright green under UV light. This makes it easy to determine whether leaks are coming from the vehicle's coolant system or some other system like the air conditioning.
The dye also aids law enforcement officers in recreating accident scenes where one of more vehicle's radiators are damaged during impact. UV light allows the investigation officer to precisely determine exactly where the car was positioned when the radiator ruptured. This can often remove all doubt about who crossed the center line or failed to yield right of way.
Dyes are also available at auto parts stores that can be added to automotive air conditioning systems to aid in determining the source of leaks using UV light.
Step 19: Mineralogy
UV light can be used to identify various minerals by their fluorescence under UV light.
Step 20: Gemology
Picture 1 - About 25 percent of all diamonds fluoresce. Diamonds that fluoresce usually appraise lower than diamonds that do not because they sometimes appear slightly cloudy or milky. However, they appear much brighter in natural light than they really are due to their fluorscence.
Picture 2 - The blue Hope diamond emits a brilliant blood red color under UV. Nearly all diamonds fluoresce blue.
Picture 3 - About 1 in 400 diamonds phosfloresce or glow in the dark after being exposed to UV light. This is a phosphorescent diamond in complete darkness after being exposed to UV light. For some people this makes the diamond even more valuable.
Step 21: Just for Fun
Picture 1 - Fluorescent Jello - make it using tonic water (very bitter) or vitamin B2
Picture 2 - Kryptonite Candy - look for the recipe here on Instructables
Picture 3 - Fluorscent Art - This is nothing more than fishing line stuffed inside an old light bulb with a UV LED in the bottom.
Picture 4 - Tonic water - really bitter stuff, but it glows a beautiful blue due to the quinine it contains.
Picture 5 - You can purchase UV markers that are completely invisible except under UV light. These can be a lot of fun.
Step 22: UV Scavenger Hunt
Here is a fun suggestion. Give your friends a battery and LED. Tell them to find something unusual that fluoresces and ask them to bring it back.
Step 23: Items That Glow Under UV Light
Common materials that fluoresce include:
Security Strips In US Currency
Vitamin A (beta-carotene)
Vitamin B1 (thiamine)
Vitamin B-2 (riboflavin)
Vitamin B-3 (niacin)
Vitamin B-12 (Cyanocobalamin)
Irish Spring soap ™
Some Minerals and Gems
Brown Spots on Bananas
Some Diamonds (~25%)
Olive Oil and Some Other Cooking Oils
Television and Computer Screens (Older Tube Type)
Fluorescent Light Tubes and CFLs
Rit Fabric Whitener ™
Some Fabric Softeners
Lysol ™ (Original)
Most Fishing Line
Kraft ™ Mac n Cheese powder
Most Energy Drinks
Vintage Vaseline Glass
Pine Sol ™
The tops of ornamental cabbage
Step 24: Conclusion
What I have shared here is only the tip of the iceberg. The limiting factor here is imagination and you should have plenty of that once you get started.