So to put to rest the question of if UV-C radiation is reaching the surface of the earth, and how much...

Mainstream science states that UV-C, the most destructive wavelength range in solar radiation, never reaches the surface of the planet and is filtered out by atmospheric ozone.

Well I purchased a UV-C light meter to see if that is the truth. The answer is a resounding NO.

My first reading in afternoon sun here in the desert southwest was 27 microwatts/cm2. I am guessing that high noon sun would probably produce roughly double that.

To put that into perspective, the below is the chart of maximum exposure times based on UV-C irradiance:

Permissible exposure time * Effective irradiance

(seconds) (uW/cm2)
28800 0.10
14400 0.21
7200 0.42
3600 0.83
1800 1.67
900 3.33
600 5.00
300 10.00
60 50.00
30 100.00
10 300.00
3 1000.00
1 3000.00
0.5 6000.00
0.3 10000.00
0.1 30000.00

At 27 uW/cm2, your max exposure time is about 2.5 minutes before it starts damaging your cells.

To give you another example, I have an LED UV-C sterilization lamp, and it produces 20 microwatts/cm2. The sun was producing even more UV-C than my pretty intense UV-C sterilization lamp when shined directly onto the sensor.

Notice that the sun feels hotter these days and the sting comes on much faster than it did many years ago? That's the UV-C destroying your skin cells.

Imagine what it is doing to everything else that isn't shielded from the sun outside? Would be interesting to hear how everyone's open air uncovered garden is doing this year.

So that puts it to rest. UV-C is most definitely reaching ground level, which means something is very wrong with the atmospheric ozone that is supposed to completely filter it out.

UPDATE: Took another reading during the noon hour on a partly cloudy day today. 38 microwatts/cm2.

EQUIPMENT:

[link to generaltools.com (secure)]

Specifications:

Measurement ranges: 1 to 9999 μW/cm2 (low) and 0.01 to 40 mW/cm2 (high)
Measurement accuracy: ±(4% of reading +1 digit)
Spectral range: 220 to 275 nm
Calibration point: 254 nm
Sampling time: 0.3 seconds
Memory capacity: 20 measurements, plus 1 for interval time
Interval time options: 1, 2, 5, 10 and 30 seconds and 1, 3, 5 and 10 minutes
Operating temperature: 32° to 122°F (0° to 50°C) @< 90% RH
Weight: 3.2 oz. (90g)
Power source: "9V" battery (included)

THREAD OBSERVATIONS:

Central Arizona: 27-38 uW/cm2
Northwest New Jersey: 28-39 uW/cm2
Central Florida: 42-49 uW/cm2

Last Edited by Silicon Jock on 08/26/2022 02:31 AM