What's a blacklight and how do you make one? This can be the subject of a recent MacGyver episode by which he quickly creates an improvised blacklight to find hidden messages on a wall. You are able to view the scene here— and a disclaimer, I am presently the Technical Adviser for the show. But however, there’s lots a great science in that one little scene.
OK, it’s not a really black light. It’s better to call it what it's: ultraviolet light. Let’s begin using a fast breakdown of light. Obviously, light is an electromagnetic wave (oscillating electric and magnetic fields), but in this instance the frequency is the significant facet. For a few narrow scope of frequencies, the human eye can find these waves—this is called the visible spectrum. Our eyes interpret the low frequency waves as the colour red, and the higher frequency will be purple.
Here is a picture that may be helpful.
Of course, you can break this spectrum of colors into seven parts: green, orange, yellow, red, blue, indigo, and violet. But what the heck is indigo? Really, this can break into only three shades—red, green, blue—or a thousand colors if you prefer. I tell my students there are seven shades because that many Isaac Newton needed there to be. Seven is a a number that is cool, and back in Newton’s day there were only seven regular moving things in the heavens: the Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn. Interesting fact: That’s the same order as the days of the week that are named after these items. Save that for a celebration (along with radioactive bananas).
Should you combine together these colors of light all, your brain detects that as white light. But how about the infrared and ultraviolet on the sides of the spectrum? Their names and placement in the spectrum could be described by their discovery. In 1880, William Herschel chose white light and split it in the rainbow colours with a prism. He discovered that if he put a thermometer past the reddish colour of light, it would warm up. There have to be some type of light that individuals can’t see, but that heat the thermometer up. Since it had been below red, he called it infrared. The same holds true for ultraviolet.
Because they might make some materials in your garments look like they were glowing, they used to be popular at parties. Additionally, the UV lights are utilized to discover different stuff— in an escape room or like at a crime scene.
The key to a UV light that is useful is fluorescence. But let me just speak electrons in matter. It ends up that electrons in a system that is bound can just be at certain energy levels. Further, the frequency of this light is proportional to the change in energy levels. This could be written as:
The h is generally known as Board’s continuous —but that. Typically an electron will make the quantum leap (see what I did there) from one excited state to the ground state—just one jump making one colour of light. Nevertheless, for some substances, electrons make multiple transitions to ground state. For every transition down, they generate light— frequency light that is distinct. So here’s what occurs. Some light is incident on the substance and this excites an electron. Multiple down transitions which creates distinct colours of light are subsequently taken by the electron. This method is called fluorescence.
Of course there’s a catch. So that you can get fluorescence to work, you have to begin with an increased frequency light—like violet or ultraviolet. But should this on some stuff shines, it'll generate light of frequency that is lower. UV light in, visible light outside.
Listed here is an example of fluorescing highlighter marker on a wall. You don’t see if you look with just visible light. With all UV light and the lights out shining on it, the highlighter fluoresces and you can quickly see it.
This can be actually how a fluorescent light works. For the traditional fluorescent tube lights (and the compact fluorescent lights), an internal gas is excited by accelerating electrons. This gas that is excited then creates UV light. On the inside of the tube is a white powder coating which is fluorescent. The UV light hits the coating when subsequently fluorescent and generates white light (many distinct colors combined together).
Now we eventually get to the MacGyver hack. Could you make a UV light with the LED flash on a smart phone? The clear answer is … maybe. As a way to comprehend this hack, you need to comprehend how an LED operates. The Light Emitting Diode is definitely a diode—a solid state device. The LED creates light in a similar manner to excited electrons in a neon gas tube (you’ve seen these neon signs). Nevertheless, for the neon light energy levels change in the atomic level. In an LED, the electrons change energy levels in a solid state material. Really, that ’s the only difference. However, this means the frequency of light generated from an LED is determined by the value of the energy transition. You only get one transition and therefore just one color of light.
How would you make a white LED light? They are now —but how do they work? Obviously you can get a green red and blue LED and combine them together to create a white light, but that most of these operate. A white LED is a purple or ultraviolet LED with a substance that is fluorescence. The LED generates a high frequency light (either violet or UV) and this makes the stuff fluoresce to create other colors (lower frequency).
Since this fluorescent material isn’t 100 percent efficient, some of the UV light could pass through and be mixed in with all the white light. There are some materials—like fluorite or fused quartz that do precisely this and may be used to make some UV photos that are fairly cool. But could there be other stuff that might do the job? Possibly. Floppy disks that are distinct uses different stuff and this round disc might let UV to pass while blocking light that is visible.
How about a quick review. Here’s how you make a UV light with a smart phone.
- Start with a smart phone that has an LED light (for the camera flash). You want two things from this light. First, it should be a UV LED with fluorescent material and second it shouldn’t be 100 percent efficient.
- Next find some material that blocks visible light but not UV—this might require some trial and error.
- Turn off the lights. Why? If you don’t the UV light will still fluoresce some stuff that you want to look at, but you won’t be able to tell since there will be all this other visible light reflecting off stuff.
I'm likely to show you a fairly cool demonstration of fluorescence. I’m going to take it and beam the red light on things that are different I will find. You must note that regardless of that which you shine this red laser on, you get a red dot.
There should be no surprises with the red laser. But what about a green laser? Take your green laser and shine it. You are looking for things which possess a non-green dot to them. Specifically, attempt beaming the laser that is green on orange plastic material. It's this that you're able to see.
Discover that for some materials the laser dot isn’t green? Yup, that’s fluorescence. Now for the blue laser using an even higher frequency.
Notice that again the blue laser causes fluorescence —but with a higher frequency light, it may compel the consequence in a more extensive variety of materials. Go ahead and seek out other materials that cause fluorescence. Make use of the blue laser as you are going to be able to discover more items. You may be surprised to find things like olive oil and some wines can try this.