50 plastic UV beads, supplied in a small plastic pot.
Normally the beads are just white. But when you expose them to Ultra Violet light - sunlight is fine - they change colour.
The beads are very sensitive to UV light, and once they have changed colour, they take a while to go back to their white state.
There are five different colours, blue, purple, yellow, orange and red.
How do they work? Well normally you can't see Ultraviolet Light - it is beyond the visible spectrum. However there are some substances that absorb UV light, and convert it to a longer wavelength, i.e. visible light. So really, we are making the invisible (UV light) visible.
There used to be a clothes washing powder in the UK that was advertised as being 'whiter than white.' You might say that is just impossible, just a bit of advertising spin. However the addition of 'whiteners' had the same effect - once the clothes had been washed, as well as reflecting white light, they also changed UV light into white light, and reflected that as well. So in a sense they really were 'whiter than white.'
Either make a fun bracelet that will change colour when you go outside, or you can do some more scientific experiments, to test if sunscreen lets UV light through. You can also test your sunglasses!
UV beads consists of 50 plastic UV beads, supplied in a small plastic pot.
Made in UK