1. Ultraviolet Waves Learning Objectives
To understand that ultraviolet waves can cause suntan and sunburn
To understand how to protect yourself from sunburn
We are now concentrating on ultraviolet waves which has more energy than visible light
Increasing frequency hence
Increasing energy

2. UV Waves
Ultraviolet waves have a number of everyday uses including forgery detection and optical brighteners in washing powder . However the greatest source of UV is from our sun.

3. UV & Humans : Suntans
Much of the UV from the sun is currently blocked by the Ozone layer (more later).
When human skin is exposed to UV the skin produces a pigment called melanin which results in a suntan
Tanned skin absorbs the radiation so the UV does not reach the lower layers causing sunburn and skin caner

4. UV & Humans : Sunburn
To much exposure to the UV in sunlight initially causes painful sunburn

5. UV & Humans : Sunburn
To much exposure to the UV in sunlight initially causes painful sunburn

6. UV & Humans : Skin Cancer
Regular overexposure to the UV in sunlight can cause early skin aging & lead to skin cancer which can prove fatal

7. UV & Humans : Skin Cancer

8. Protecting against UV
The easiest way to avoid sunburn and other skin damage is to take the following precautions
Stay out of the sun at midday
Stay in the shade
Cover up : clothes & wide brimmed hats
Limit time in the sun until tan develops
Apply a high factor sunscreen

9. Protecting against UV

10. Sun Index A measure of how strong/burning the strength of the sun is
Risk
1-2
Low risk
3-4
Avoid being in the sun for more than 1-2 hours
5-6
Burns in 30-60mins
7-10
Severe burns in 20-30mins
These times are for someone with untanned white skin who burns easily

11. Sun Protection Factor (SPF)
The Sun Protection Factor (SPF) is a measure of how much protection a particular sun cream offers... How much longer you can stay in the sun without a risk of burning
Safe time in sun with cream = SPF x time given by sun index

12. SPF Worked example
If the weather forecast predicts that the sun index will be 7 what is the longest time an untanned white person can stay in the sun if they correctly apply sun cream with SPF 15?
Safe time in sun with cream = SPF x time given by sun index
Safe time in sun with cream = 15 x 30
Safe time in sun with cream = 450 mins