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Safe and Sound
Blog Safe and Sound - Ultraviolet Light Tests - blog 22
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  • Author Author: dougw
  • Date Created: 3 Jul 2017 7:40 PM Date Created
  • Views 1143 views
  • Likes 9 likes
  • Comments 7 comments
  • safe and sound
  • doug wong
  • invisible hazards
  • uv index
  • safe and sound design challenge
  • hazardous_environmental_factors
  • safe & sound
  • wearable technology
  • uv sensor
  • Wearables
  • safe&sound
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Safe and Sound - Ultraviolet Light Tests - blog 22

dougw
dougw
3 Jul 2017

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

................

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)

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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 dwinhold 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

image

image

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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Top Comments

  • dougw
    dougw over 8 years ago in reply to dwinhold +2
    Good idea dwinhold - I could spread them on a clear surface over the sensor. I can measure before and after the application. I'll have to wait for another sunny noon-hour to test though...
  • DAB
    DAB over 8 years ago +2
    Hi Douglas, You could have done a good demo under the clouds as well. UV is just as bad on a cloudy day as a sunny one. I got a really bad sunburn on an overcast day, thinking I was safe. I was not. Great…
  • dwinhold
    dwinhold over 8 years ago +1
    Another great demo of your incredible project!! Is there a way to test sunscreens to see how effective they are? Dale W
  • DAB
    DAB over 8 years ago in reply to dougw

    Hi Douglas,

     

    Do you have any deep blue photography filters?

    Some of them do a good job of cutting the visible light down even more, but you have to be careful as some passed a lot of IR.

     

    If you have a UV block filter for your camera, you can do some rough calibration by using it to take before and after readings and then subtract the value you get with the UV blocked.

     

    DAB

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  • dougw
    dougw over 8 years ago in reply to DAB

    I don't have any way to measure the sensor response curve, but the data sheet indicates its bandpass is pretty good for UV:

    image

    However, although this curve looks good, UV is only 5% of solar radiation, so this device attenuates other wavelengths by a factor of 10 to 20, but the other wavelengths could have 20 times more energy, so to me this means the sensor is still reading some regular light as well as UV.

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  • DAB
    DAB over 8 years ago in reply to dougw

    Yes, with UV, it is knowing which specific wavelengths are getting through.

     

    Your sensor is probably only detecting a narrow region.

     

    If it has a broad enough wavelength detection capability you could use two of them with some filters to calculate the real danger exposure ratio.

     

    DAB

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  • dougw
    dougw over 8 years ago in reply to DAB

    I've been burnt on cloudy days too and I don't burn too easily, but my sensor indicates the UV index goes down with cloud cover. For example from 6 to 2. Of course not all clouds are equal in this respect, so it is tough to get a meaningful measurement.

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  • DAB
    DAB over 8 years ago

    Hi Douglas,

     

    You could have done a good demo under the clouds as well.

     

    UV is just as bad on a cloudy day as a sunny one.

     

    I got a really bad sunburn on an overcast day, thinking I was safe.  I was not.

     

    Great demo.

    DAB

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