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  • Author Author: dougw
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Safe and Sound - Ultraviolet Light Tests - blog 22

dougw

I have been waiting for a week to do some ultraviolet light tests - the sun just never seems to shine when I need it.

I calibrated the UV sensor output to match the UV Index and wanted to test it in real sunlight.

The UV Index was developed in Canada in 1992 and subsequently adopted by the World Health Organization and the World Meterological Organization in 1994.

This table shows the UV Index scale and what it means:

UV Index

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Media graphic colorRisk of harm from unprotected sun exposure, for the average adultRecommended protection
0.0–2.9Green"Low"A UV Index reading of 0 to 2 means low danger from the sun's UV rays for the average person.

Wear sunglasses on bright days. If you burn easily, cover up and use broad spectrum SPF 30+ sunscreen. Bright surfaces, such as sand, water and snow, will increase UV exposure.

3.0–5.9Yellow"Moderate"A UV Index reading of 3 to 5 means moderate risk of harm from unprotected sun exposure.

Stay in shade near midday when the sun is strongest. If outdoors, wear sun protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 30+ sunscreen every 2 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water and snow, will increase UV exposure.

6.0–7.9Orange"High"A UV Index reading of 6 to 7 means high risk of harm from unprotected sun exposure. Protection against skin and eye damage is needed.

Reduce time in the sun between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 30+ sunscreen every 2 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such sand, water and snow, will increase UV exposure.

8.0–10.9Red"Very high"A UV Index reading of 8 to 10 means very high risk of harm from unprotected sun exposure. Take extra precautions because unprotected skin and eyes will be damaged and can burn quickly.

Minimize sun exposure between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 30+ sunscreen every 2 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water and snow, will increase UV exposure.

11.0+Violet"Extreme"A UV Index reading of 11 or more means extreme risk of harm from unprotected sun exposure. Take all precautions because unprotected skin and eyes can burn in minutes.

Try to avoid sun exposure between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 30+ sunscreen every 2 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water and snow, will increase UV exposure.

The weather forecasts here show the UV Index for every hour.

In the video below, I strapped the wearable sensors to a beer stein so they could be consistently aimed at the sun and stationary for the video.

Note that the MQTT subscriber shows the UV Index with more resolution in case it is of interest. (delayed of course by about 11 seconds due to publishing schedules)

The video demonstrates sunglasses and clothing work well to reduce UV exposure.

By the way it is pretty cool that the system can access my Wi-Fi quite far from the house.

 

UPDATE

I did a quick experiment on suggestion to see if I could measure sunscreen lotion performance.

In the following 3 images the actual UV Index is always 5.48 as shown in the first image with no sunscreen.

The second image shows the reading with a clear plastic sheet over the sensor. (It attenuates the UV Index to 4.52)

The third image shows the reading with a clear plastic sheet plus SPF30 sunscreen lotion. (It attenuates the UV Index to 3.11)

The sunscreen lotion was applied in a thin coating - hard to measure or describe the thickness of the coating, but is visible in the images on the right side of the plastic sheet.

image

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If the readings are accurate the clear plastic reduced the UV Index by 0.91 and the sunscreen lotion with plastic sheet reduced it by 2.37.

Therefore the sunscreen lotion is contributing a reduction of 1.41 in the UV Index. I suspect the influence of visible light is making these differences smaller than true values, but even in this test sunscreen lotion significantly outperformed the plastic sheet.

image

 

All links to blogs related to this project can be found in the first blog here:

Safe and Sound - Invisible Hazardous Environmental Factors Monitoring System - blog 1

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