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Congratulations on receiving one of our torch kits! It's super simple, but you've actually got two kits in one! You can create your kit as a normal visible white torch, or instead turn it into one that uses a special type of light called ultraviolet (UV) light that can show secret invisible marks in the world around you!
We suggest you make this when you get home - you'll need a dark environment to see the magical effects of UV light so you'll want to wait until night, or go into a dark room and draw the curtains!
If you like technology and making things, you might also like to check out our holiday Tech Camps, where campers aged 9-17 build 3d printers, robots, RC cars and much more. We've setup a special discount code for you: use code EIJ24 for £75 off any camp of your choice.
Light is all around us but we sometimes take it for granted. What we think of as light is really only part of a wide band of ‘stuff’ known as the electromagnetic spectrum. This spectrum comprises of x-rays and gamma rays at one end, and radio waves at the other. Between these is a thin band that makes up what we can see, from violet at one end through to red at the other.
Just past red in the spectrum is infrared. Common TV remote controls use this form of light to communicate with the TV. Although our eyes can’t see it, by looking at the end of the remote control through a mobile phone camera or webcam you can make it visible; these cameras are sensitive to wavelengths (colours) of light that our eyes can’t see. As you get further away from the colour red, you reach ‘far infrared’ which all objects emit. These rays can be detected with special thermal imaging cameras that police can use to see criminals in the dark, and scientists can use to look at the heat escaping from houses and other objects.
At the other end of the spectrum is ultraviolet. The torch you will be building produces 'near ultraviolet' light, or ‘UVA’, which is very close to the colour violet (or purple) so is still just visible to our eyes. This sort of ultraviolet light is not dangerous unlike the shorter-wavelength ‘UVB’ and ‘UVC’ light which can cause sunburn and skin cancer. It is however just far enough away from the normal visible light we see to show some interesting effects.
First of all, let's see if we can get the two LEDs (lights) that are in your kit working! Take one of the LEDs and place the coin cell (battery) between the two legs as shown. N.B. It will only work one way around - if it doesn't work first time, try turning the battery upside down and inserting between the legs again! You should find that the longer leg of the LED has to be touching the positive end of the battery (the side marked with a '+').
If you're in luck you should see it glowing white or purple! Our one below is glowing white and we're looking for the purple one, so we'll put the white one aside for now and use the purple one instead. N.B. Our pictures will show the white one because it shows more clearly in a photo, but make sure you're using the purple one!
Now we're going to get the small paper ring and insert it under the top (shorter) leg as shown.
When you push the ring all the way under the top leg, the LED should now not be lit any more. Actually if you squeeze the center of the ring where the legs are, you should be able to make the LED light again whilst you are squeezing. This is intentional - we've made a simple switch!
Now find the plastic piece that looks like the one shown. Yours might be a different colour, but the important thing is that you use the piece with the raised circular rim. It should look like the one below.
Fun fact : These plastic pieces are actually 3D printed using the 3D printer that our campers make in the 3D printing course. It's one of our most popular courses because campers get to take their printers home so can design and make things like this torch themselves! We use the same 3D printers to make parts for many of our kits and courses, including the Drone Racing and Robotics courses. 3D printing is a great technique to make anything from toys and tools to idea for products that you cand design, print and even sell yourself!
Carefully insert the assembly you have made into this plastic piece as shown. This is the most fiddly step! The coin cell has to fit in the space in the middle and the LED should fit in the space at the end of the torch as shown. You might need to squeeze the legs of the LED down flat to get them to fit nicely.
We're about to complete the assembly, but do another test by squeezing the legs - your torch should light up!
Now find the matching second plastic piece. Look at it carefully - it should have a recess for the LED on one end and a hole on the other - you'll need to make sure these match up with the other piece when you connect them in a minute ...
Make sure they're completely aligned, and then squeeze them together as shown below. Ours isn't completely closed yet as there is still a gap showing between the two halves ...
Once you've squeezed it fully closed, you're ready for some fun experiments with UV light ...
Remember - you'll need a dark environment to see the magical effects of UV light so you'll want to wait until night, or go into a dark room and draw the curtains to see some of the effects described below.
There are secret symbols on all sorts of things - UK and foreign bank notes, passports, drivers licenses, credit cards and even stamps (UK 2nd class stamps have a stripe down the middle). Tonic water glows (only slightly though), and you might find other things yourself! Even the marks on (posted) envelopes may glow.
What you're seeing here is an effect called fluorescence. The inks used in these objects absorb one colour of light (in this case UV) and emit another in the visible spectrum.
Highlighter pens also fluoresce under UV light - a fun thing is to draw a skeleton on the back of your hand with a yellow highlighter - it will be pretty hard to see under normal light but will glow strongly with your UV torch.
If you have anything made of glow in the dark material you can write on it using your UV torch held right against the surface. The writing will fade over time. The UV light 'energises' the glow-in-the-dark substance, and it gives out light of a different colour (usually a yellowish green). This is an effect related to fluorescence, called phosphorescence.
Some flowers have UV markings on them - scientists think that this might be to make them more attractive to insects who help pollinate them. Some minerals also fluoresce under UV light and geologists can use this effect to identify them. We've had a quick look outside and haven't found anything ourselves in the UK, but if you do, please do let us know - we'd love to hear.
Even some animals glow under UV light. Many scorpions do, but if you are in the UK, you may unfortunately (or perhaps fortunately) be lacking in having many local scorpions around!
The torch that you built makes a simple electric circuit. They use a coin cell (battery) and an LED (light emitting diode). It is a special LED that emits light at around 390 nanometres (nm) which is just between the UV and visible spectrum. Normally such a simple circuit wouldn’t be recommended; LEDs generally need a device called a resistor to be connected in series to limit the current so that they don’t quickly burn out. In this circuit however the resistor isn’t needed because the LED draws very little current; mainly because the voltage of the battery (3V) is only just approaching the voltage needed to make it turn on. This means that the LED glows only dimly, but it also means that the battery will last for a very long time; probably for several years in typical use.
The card disc and the leads of the LED act as a switch; they are normally separated from the battery by the disc, and are pushed towards it when the torch is squeezed.
A couple of other suggestions - try looking at washing powders under the light; they usually contain optical whiteners which will fluoresce as well; this is how they make your clothes look "white and brighter!". You can also buy fairly cheap invisible ink pens that glow under UV light. People sometimes use these to security mark their valuables.
Also .... (only for those with a strong stomach) ... some bodily fluids fluoresce under UV light - urine is one of them! If you want to see how well your loos are cleaned, turn off all the lights on a dark night and use your torch to see if you can find anything glowing! (yuck!) It is easiest to see this effect on darker materials such as wood. Do note however that there may be other substances that fluoresce in a bathroom including splatters from some substances like soap.
We would really love to hear if you discover anything under UV light that we haven't mentioned!
Once you've explored the world of UV, you might like to swap out your UV LED for your white one and just make a normal visible torch! You should be able to separate the two halves of the plastic by prying them apart on the end of the torch where the mounting hole is. (There's a little 'bevel' here that makes it easier to get your fingers in between them! (Try using your thumbs and dig in with your nails into this little bevelled part).
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