Biology 11–12 · Year 12

Ultraviolet protection measured with UV-sensitive beads under sunscreens and fabric

Module 8: Non-infectious Disease and Disorders (Causes and Effects: diseases caused by environmental exposure; Prevention)

Practical, model not builtLow risk

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The idea

Ultraviolet radiation, the main environmental cause of skin cancer, can be detected by beads that change colour, and the reduction in colour change under a sunscreen or fabric shows how much ultraviolet it screens out.

Safety card

Low riskAn adult supervises

Hazards

Learners' own ultraviolet exposure outdoors
UV-A lamp near eyes
Skin sensitivity to sunscreens

Controls

Keep outdoor time short and in hats and sunscreen; set the bags out and wait in shade
Never look into the lamp
The sunscreens under test go on the bags; learners wear their own sunscreen and hats

Note

No hazardous chemicals; RiskAssess (https://www.riskassess.com.au/).

What you need

UV-sensitive colour-change beads or UV-sensitive paper (the Cancer Institute NSW method)
Clear zip-lock bags or sheet protectors, one per treatment; permanent marker
Sunscreens of SPF 15, 30 and 50 in lotion form; a spray sunscreen; sunglasses; samples of school uniform fabric
Sunny outdoor area at midday with a UV Index of 3 or more (checked on the day), or a UV-A lamp; hats and sunscreen for learners

How to do it

Place five beads in each bag and label one bag per treatment on one side: control, SPF 15, SPF 30, SPF 50, spray, sunglasses, fabric.
Spread each sunscreen evenly over the unlabelled side of its bag; cover the sunglasses and fabric bags with the item itself.
Record predictions, then place all bags in full sun (or under the lamp) together for the exposure time the bead instructions give, usually 1 to 10 minutes.
Score the colour of each bag's beads against the control and an unexposed set on a 0 to 4 scale, with two observers scoring independently.
Enter the day's UV Index in the model to calculate the erythemal dose reaching skin in an hour with and without each SPF.
Relate the result to the Slip, Slop, Slap message and to why sunscreen is one of several protections.

What you should see

The control beads change colour strongly within the exposure time, beads under sunscreen change less, and SPF 30 and SPF 50 are hard to tell apart by eye. The bead colour cannot rank sunscreens by SPF: the Cancer Council fact sheet's figures, 3.3 percent of ultraviolet reaching the skin under SPF 30 and 2 percent under SPF 50, rate protection against sunburn, while the beads also respond to UVA, as their change under a UV-A lamp shows, and UVA protection is rated separately as broad spectrum; beads that have reached full colour can show no further difference. At a UV Index of 10 the erythemally weighted irradiance is 0.25 W/m^2, giving 900 J/m^2 in an hour on bare skin, 30 J/m^2 under correctly applied SPF 30 and 18 J/m^2 under SPF 50 (computed from the WHO UV Index definition). The learner knows it worked when the control is the darkest and both independent observers rank the treatments the same way.

What changes

What you change: protection (none, sunscreen SPF, spray, sunglasses, fabric)
What you measure: colour-change score of the beads
What you keep the same: exposure time and position
number of beads
sunscreen thickness
time of day

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

A cool or cloudy day is safe from ultraviolet; ultraviolet does not depend on temperature and the UV Index can be high on cool days.
SPF 50 stops all ultraviolet; it transmits about 2 percent, so other protection still matters.
Sunscreen lets you stay in the sun longer safely; the WHO guide warns it should never be used to prolong exposure.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Biology Stage 6 Syllabus (2017), current: Year 11 taught to the end of 2026 and Year 12 to Term 3 2027BIO12-15 BIO11/12-5
Biology 11–12 Syllabus (2025), Year 12 focus area Diseases; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-12-02
Biology 11–12 Syllabus (2025), Year 12 Working scientifically; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-12WS-02 BI-12WS-03 BI-12WS-05
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

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