UV (Fluorescence)

Introduction
Public summary: 

The world looks different when it's lit by UV... see how you can use this type of light to make clothes look extra-bright, find out whether banknotes are real or fake, and revive dead glowsticks.

Looking at how materials fluoresce in UV light.
Useful information
Kit List: 

Short blue box containing:
Shrouded UV lamp
White paper
Washing powder tablets
Glowsticks
Highlighters
Sun cream
Board coated with glow in the dark paint
Also useful:
Paper money, driving license (anything with UV security markings)

Packing Away: 

There's a packing diagram on the side of the box, but basically:

In the bottom: Bottle, glowsticks, highlighters, power lead, all the other small things
In the middle: UV box
On the top: The painted board

Frequency of use: 
5
Explanation
Explanation: 

In a nutshell..

Show kids that there's more to light than the colours that they can see- and how this can explain why some ordinary things glow in "black light"

How to set up the equipment

This is best set up on the floor so that you don't look directly at the bulb. Put the lead and switches of the box towards you, with the flat side of the box towards your audience. The experiment is better in a dark corner/ in a dedicated dark room area. See the Risk Assessment for more details, but do thing about avoiding trailing wires in the dark! Also, there should be a power lead for the light box with this kit- please don't pack it with the main box of extension cables! There's lots of extra things in the box- if you keep them in the empty blue box when you're not using them it's easier to find them in the dark/ helps people avoid tripping over them!

What does the box do?

Turn over the box **with both lights switched off**, and show the kids the two bulbs. One is for "ordinary/normal" white light. The other bulb is a UV bulb- a kind of light human eyes can't see. There is a switch for each on the back. Turn it back over as soon as you're done with this to avoid UV directly into people's eyes.

See Risk Assessment for more details, but briefly: this particular UV light is pretty safe- it's not that far into the UV, so isn't as energetic/ dangerous as some other sources. You should hopefully spot that it gives off weak visible light too. It's also fairly weak - but *don't use it while it is facing up* just in case!!

What is light/ UV light?

The light most of us are really familiar with is white light. But that's actually a mixture of different colours. Most of the time we can't tell that, but sometimes we can see these colours split up, like in a rainbow.

Do you know the colours of the rainbow? Ask them to tell you!
[Red -> Orange -> Yellow -> Green -> Blue -> Indigo -> Violet (basically purple!)]

It turns out that there are more kinds of light than our eyes can see. Some kinds of light are "redder" than red is - we call that kind of light "infra-red" (there's another CHaOS experiment about this- check it out!). You might have seen images from cameras that can detect this kind of light, perhaps watching animals at night on TV, or police chase criminals with helicopters. At the other end of the rainbow there are other kinds of light that we can't see. These are more blue/ more purple than violet, and we call this kind of light "ultra violet".

It's weird to think that there's kinds of light we can't see, but not all kinds of eyes detect the same light. For example, some people can't tell red and green apart, which is called "colour blindness". Another example: some insects, such as bees, can see UV light. Some types of flowers have extra patterns in UV, so this helps them find the nectar in the middle of a flower! (How cool is that?!)

But what about wavelength/ spectra?

Add this extra level of detail with caution: it can be too much detail to take in if they've never thought about UV/ IR before, and you can overwhelm them. You can come back to this later on once you'rve showed them some of the cool things that glow!

EM Spectrum: we call all the kinds of light (including UV, IR, visible) "electromagnetic radiation". One way of understanding this is to say that all these kinds of light have different sizes of wavelength. There's some charts in the box that you can point at when you explain this. Start with the rainbow: Red light waves are wider/longer than blue light waves. Following on from that, infra-red has longer waves than red light; UV has a shorter waves than blue. If you go further outside that you can see microwaves (that you can cook with) and radio waves (which can hold information. like music). These have a longer wavelength, much longer than infra-red. If you go the other way you get to X-rays- these have smaller waves than UV!

Energy: Another way of viewing the light is as a stream of particles. We call them photons. They are like small balls travelling at the speed of light. And photons of different colours have different energy. Blue photons have more energy then red ones and ultra-violet ones have even more energy. This if why UV can cause damage to your skin. (You can use analogy with a light and heavy ball. The heavier has more energy and can harm you more if thrown upon you.) It causes damage to the cells (which can cause cancer if it goues really bad). When you get sun burned you have absorbed too much of UV. So wear suncream to prevent this!
(And X-rays have even more energy and do not stop on your skin - they can go through your body so you can use them to see what is inside. But they are also more harmful and that is why it is used as little as possible.)

Some things glow if you put them under UV light

Put an object from the box under the UV light. Boring old white paper works- though pretty patterns on driving licenses/ credit cards/ banknotes are a good start if you have them! Either way, this first item should glow! Here's a way of explaining this...

1) Turn on the UV light
2) Place a (fluorescent) object underneath it - it should glow.
3) What's happening? How can we see glowing if we can't see UV?
4) It's fluorescence! (Use this word! Here's a simple explanation- let us know if you have an alternative!)

The object absorbs or takes in light that we can't see- UV light. The object can then change the light from UV to a kind we can see. The energy in the UV light is being converted into a different visible form, and things that do this are called fluorescent.

Wikipedia has a more precise explanation, but it depends on understanding lots of other technical words!
"Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation."
(From http://en.wikipedia.org/wiki/Fluoresce)

Where are UV lights used in everyday life?

In shops, to check if money is fake! (See markings on banknotes)

Ask if they've ever seen notes being checked in shops.You can ask parents if they have a five pound note you can borrow briefly. If you look at the note, there are all kinds of features visible to the eye (metal strip, watermark etc.) but if you put the note under the UV light, you can see extra information, like the value of the note. This is useful in preventing forgery because printing with UV sensitive ink is difficult and expensive. Again, the UV gives the special inks energy so they give out light. Don't forget to give the fiver back

In discos, to make white things look super bright!

You might have seen this!

Fluorescent objects in the box

Highlighters:

Fairly boring in white light, but spectacular under UV. Draw on white paper or non-fluorescent card, on even a smiley face on the back of your hand!

Glowsticks:

- show them glow sticks in the UV - which will glow. Glow sticks get their energy from a chemical reaction rather than UV, if you give them energy from UV they will still glow though

Tonic water

This is probably the brightest fluorescence in the box, so I usually leave it until last. It's quinine that's causing the glow- this compound is more famous for helping to kill malaria parasites when it was added to tonic water. In the past it was in much higher doses than it is now.

For more info on tonic water visit: http://en.wikipedia.org/wiki/Tonic_water

Washing powder

Residual powder makes your clothes look whiter by helping balance out the yellower colours of sad old white clothes.
**This gets everywhere, need to replace blocks!!**

Phosphorescent things in the box

Phosphorescence is very like fluorescence a chemical in the paint absorbs energy from the UV light, but instead of releasing it again in miliseconds, it releases it slowly over minutes.

Glow in the dark stars:

As above!

Glow in the dark paint: tube (not presently available)

Apparently this stains, so don't open the tube! (There is some phosphorescent paint, this does the same thing as fluorescent dyes but releases the energy much more slowly -> glow in the dark stars etc. NB: this should be well wrapped in plastic (whilst being non-toxic it is very staining) - you can often see it glowing through the container.)

Glow in the dark board

There is also a board coated with the phosphorescent paint - put it under the UV light for 10 seconds (or more - doesn't do any harm), then turn the light off and let them see how the board carries on glowing. Turn the light back on and invite them to put their hands on the board. Make sure they keep their hands in the same place for at least 10 seconds, and see if they can guess what the board will look like after they take their hands away - the effect will be most long-lasting if you turn the UV light off at almost the same time as they take their hands off the board. Some parents may want to take photos!

Why is there sunscreen in the box?

- UV light from the sun (not this box, so it's safer than sunlight!) has lots of energy. This damages your skin (or cells, and ultimately, the DNA) when you absorb/ take in too much of this.
- If you use sun screen it can absorb the UV/ block it from reaching your skin, which reduces the damage the sunlight can do
- See this in action: spray a white sheet of paper with a bit of sunscreen. Predict what will happen (should look black). Try it under the light.
- Try drawing with the sunscreen- you can write hidden messages!
- Combine this with highlighter pens- you should be able to block fluorescence.
- Try not to use too much sunscreen -it's pretty expensive...

================
Bits of an old explanation- should all be in section above!

I start off trying to get the idea across, that UV is a colour, but you just can't see it..

What colours are there in a Rainbow? -> ROYGBIV..

Have you thought that there might be some other colours that you can't see? If they are older ask them if they have heard of infra red, microwaves, radio waves, X-rays, UV -> they are all colours of light that your eye can't see

Mention that bees can see UV- they seem to get a kick out of this. Some flowers that look plain white to us literally have landing stripes on for bees.

Explain that the tube gives off UV and show them what happens when you put the paper in the UV. This is because when UV hits the paper it gives it some energy, which it can release as blue light...

Do you know what UV does to your skin? normally they don't

What happens to your skin if you stay out in the sun too long -> sunburn -> Due to UV
Sun cream

What do you put on to stop you getting sunburnt? -> sun cream

What do you think it does to the UV? -> Stops it

What do you think will happen if we put sun cream on the paper? Quite often they work out that it won't glow

Get them to draw stuff on the paper with the suncream then put it in the UV light -> dark lines. Which I was impressed with the first time I tried it.

It's always more striking if you do the drawing-on-the-paper-with-suncream in the light (take them outside the darkroom) and then bring the paper in... in the darkroom it's harder to see how little difference the suncream makes to visible light. Which I (and lots of parents) think is really cool... sometimes I manage to convince the kids, too.
If you've got a group working round the darkroom experiments it's worth being aware what they've already had demonstrated to them, as if they've seen, say, polarised light, they should (OK, might) have some idea about what (you want them to tell you) light is.

Fluorescent things

Get them to play with the highlighter pens (they are much more impressive on paper or cardboard that doesn't glow)
Glow sticks get their energy from a chemical reaction rather than UV, if you give them energy from UV they will still glow though
Paper money and driving licences (security marking)!
Driving licences also have patterns only visible in UV.

Links to IR
This experiment often links well if placed near IR or demonstrated as a pair. You'll find the lights in IR can be too bright to see UV florescence. If separate demonstrations try and place slightly further apart or use the boxes as a screen otherwise switch them off as you move across.

Risk Assessment
Date risk assesment last checked: 
Sat, 27/01/2018
Risk assesment checked by: 
hannah_thorne
Date risk assesment double checked: 
Mon, 29/01/2018
Risk assesment double-checked by: 
lucyhart.042
Risk Assessment: 
DESCRIPTION Use UV light to observe effects of suntan lotion and other samples
RISKS
  • 1. Electrical hazard
  • 2. UV light
  • 3. Trip hazard
  • 4. Broken tube including mercury
  • 5. Risk of ingestion of washing powder sample, or getting it into eyes.
  • 6. Some people have an allergic reaction to suncream. Avoid getting in eyes.
  • 7. Risk of ingestion of split glow stick - chemicals can cause irritation to skin and eyes and vomiting if ingested.
  • ACTION TO BE TAKEN TO MINIMISE RISKS
  • 1. Use covered tube. Set up of box keeps lamp off possibly wet floor. Ensure has passed PAT test. Read separate electrical parts RA.
  • 2. Use soft UV - our UV tube was on sale to the general public so the wavelength is at the safer end of the UV spectrum. The experiment is set up so that it is not easy to look directly at the UV light. Warn users not to look directly at it. Avoid prolonged skin exposure. Read separate darkroom risk assessment.
  • 3. Place wires sensibly (not across middle of room), and put the UV light in a place it is not likely to get trodden on. Tape down if necessary.
  • 4. Tube is inside the light box to protect it.
  • 5. Washing powder to be kept in a sealed clear plastic bag. (think it may be located in a clear plastic tube now?)
  • 6. If children want to put suncream on their skin, first make sure that they've previously used suncream without allergic reaction.
  • 7. Don't let children repeatedly play with and bend glowsticks
  • ACTION TO BE TAKEN IN THE EVENT OF AN ACCIDENT
  • 1. Call first aider in event of injury.
  • 2. Call first aider in event of injury.
  • 3. Call first aider in event of injury.
  • 4. If lamp becomes broken, keep the public well away from the area, and ventilate area where breakage occurred. Take usual precautions for collection of broken glass. Do not use a standard vacuum cleaner for cleaning up dust; instead, pick up pieces/dust with a damp cloth or damp paper towels. Place materials, including the cloth/towels, in a sturdy closed container to avoid generating dust. After you have picked up all that you can, then vacuum the area. Finally, ventilate the room where the breakage ocurred.
  • 5. Call first aider in event of injury, who may perform an eye wash if trained and confident to do so.
  • 6. Call first aider in event of injury, who may perform an eye wash if trained and confident to do so.
  • 7. Make sure anyone in contact with the glow stick washes their hands immediately and clear up spillages before continuing. Call first aider in event of injury.
  • This experiment contains mains electrical parts, see separate risk assessment.
    This experiment is sometimes run in a darkroom, see separate risk assessment.
    Images
    Publicity photo: 
    Experiment photos: