Spray Vs. Lotion: The Effect of Sunblock on UVA and UVB F. Allaire, A. Suenobu, L. Wells PHYS 399 Summer ’09
Spray Vs. Lotion: The Effect of Sunblock on UVA and UVB
F. Allaire, A. Suenobu, L. Wells PHYS 399 Summer ’09
Ultraviolet Radiation
Ultraviolet (UV) ultraviolet light is the light just past the wavelength of the color violet on the electromagnetic spectrum
UVA frequency ranges 400 - 320 nm
UVB frequency ranges 320 - 290 nm
UVC frequency ranges 290 - 100 nm (these waves are absorbed completely by oxygen and the ozone layer)
UVA –responsible for suntans and
premature aging of the skin and some cancers
UVB associated with sunburns, cataracts and skin cancer
Why should we care about UVA or UVB radiation?
Premature aging of the skin Damaging the skin’s cellular DNA Various forms of skin cancer Eye damage including cataracts Reddening of the skin and sunburn
Protective measures
Wear clothing with Use sunglasses Seek shade Wear hats SPF - Sun Protection Factor
The Skin Cancer Foundation maintains that SPF’s of 15 or higher are necessary for adequate protection.
Purpose
We know that sunscreen does protect. The purpose of this experiment is to determine if there is a difference in effectiveness of protection from UVA and UVB radiation between lotion or clear spray-on sunblock.
Hypothesis
We predict that the lotion would provide more protection than a clear spray-on sunblock of the same SPF value.
Experimental Design
Independent variable: Lotion / Spray-on Sunblock
Dependent variable: UVA, UVB penetration (mW/m2)
Constants: Time of day, amount of sunblock, length of time, SPF, brand, multiple trials using same procedure for each trial,
Control: Clear plastic –no sunblock
Experimental Design
Spray
Lotion
Control
Experimental Design
UVA and UVBProbes and the LabQuest handheld device.
The application of sunblock
Lotion Spray
Setting up in the sun….
Data collection:
Day 1 – Ran 3 trials beginning at 9:55 am until completed.
Day 2 - Ran 3 trails beginning at 10:30 am until completed.
Averages were then made using all 6 trials for the 2 days the experiment was conducted.
We worked carefully to keep all other variables to a minimum.
Variables that could affect results…
Cloudy day!
Variables that could affect results…
The amount of spray:
Two pumps of the spray bottle from the same distance away from plastic!!
Variables that could affect results…
The amount of lotion:
Small amount each time on fingertips applied with the same pressure onto plastic.
UVA:Comparing spray, lotion and control
UVA:Comparing spray and lotion
UVB:Comparing spray, lotion and control
UVB:Comparing spray, lotion and control
Now for some numbers…
UVA UVB
Sunblock Irradiance (mW/m2)
% Total Irradiance (mW/m2)
% Total
Control 7181.645 100 341.9 100
Lotion 159.673 0.022 13.8 0.040
Spray 272.284 0.038 13.3 0.039
Conclusions Our hypothesis was refuted
Difference between spray/lotion and control is significant
Difference between spray and lotion seems insignificant
Wear something!
Extensions Compare brands that have same SPF
value Compare various SPF values Compare time after application Sunblock vs. SPF clothing/sun glasses Effectiveness after water immersion Amount of lotion/spray applied Price vs. effectiveness
Student Research Informal survey: How many students
wear sunblock? Data from this experiment can be used
as a demo to introduce the topic. Students will design and conduct
experiments based on extensions provided in the conclusion.