<p>In addition to radiant exposure, for certain locations, some meteorological services record hours of sunlight for periods during each day when the <a href="http://www.bom.gov.au/climate/austmaps/solar-radiation-glossary.shtml#radiationunits" rel="nofollow noreferrer">solar radiance</a> equals or exceeds ${120\ \rm{W/m^2}}$. The weather observations for Sydney airport, for June 2015 can be seen <a href="http://www.bom.gov.au/climate/dwo/IDCJDW2125.latest.shtml" rel="nofollow noreferrer">here</a>. Column 7 lists the sunlight hours for each day listed.</p>

<p>In terms of measuring data from the electromagnetic spectrum, ultraviolet radiation levels are measured, but not levels of light visible to the human eye.</p>

<p>In Australia, the Bureau of Meteorology measures the hours of sunshine each day but the <a href="http://www.arpansa.gov.au/uvindex/index.cfm" rel="nofollow noreferrer">Australian Radiation Protection and Nuclear Safety Authority</a> measures and records ultraviolet radiation levels.</p>

<p>Real time measurements for 11 locations are posted on this <a href="http://www.arpansa.gov.au/uvindex/realtime/index.cfm" rel="nofollow noreferrer">site</a>.</p>

<p>This is snap shot of the data for Alice Springs. The yellow/orange line is the forecast UV and the pale blue line shows the measurements.</p>

<p><img src="https://i.sstatic.net/GKw2C.gif" alt="enter image description here"></p>

CC BY-SA 3.0
2015-06-13T01:55:36.763Z
2017-03-02T08:50:08.597Z
2017-03-02T08:50:08.597Z
Fred
<p>It can be measured in units of energy per surface area, for example, <strong>kWh/m<sup>2</sup></strong>.  The official SI name would be <a href="https://en.wikipedia.org/wiki/Radiant_exposure" rel="nofollow noreferrer">radiant exposure</a> but I haven't seen that phrase used in a climate or weather context.</p>

<p>For example, here is a map by NREL of average radiation per <em>day</em> in the US for July:</p>

<p><img src="https://i.sstatic.net/vCvbN.jpg" alt="NREL map of radiation in the USA">
<br />(Source: <a href="http://www.nrel.gov/gis/solar.html" rel="nofollow noreferrer">National Renewable Energy Laboratory</a>)</p>

<p>And here is a map for Sweden for the same quantity per <em>year</em> (hence the much larger numbers):</p>

<p><img src="https://i.sstatic.net/fSWaY.png" alt="SMHI map of radiation in Sweden">
<br />(Source: <a href="http://www.smhi.se/klimatdata/meteorologi/stralning/normal-globalstralning-under-ett-ar-1.2927" rel="nofollow noreferrer">SMHI</a>)</p>

CC BY-SA 3.0
2017-03-03T02:55:05.420Z
Pyranometers are the typical instrument for recording insolation [incoming solar radiation] that is integrated to make the figures above.  A great place to see this data in action is the Oklahoma Mesonet, such as http://www.mesonet.org/index.php/weather/meteogram/ (bottom plot)  Clouds will greatly reduce the values, but other times they will often be slightly below maximum values simply due to atmospheric composition, things like haze and pollution\stagnation, even temperature has some bearing.
JeopardyTempest
CC BY-SA 3.0
2015-06-12T15:04:35.823Z
Thanlks @gerrit (+1) - very interesting! So what's the name of this type of metric, is it just "*solar radiation*? Or something else? Also can I assume that `0 kwH/m^2` is pitch black (no radiation/light whatsoever)? Thanks again!
smeeb
CC BY-SA 3.0
2015-06-12T15:06:47.577Z
Also, the ranges/scales on that unit are way different between to the two maps you show. For the American one, the range is between 2 and 9. For the Swedish one, they are between 700 and 1,100! Any thoughts there? Thanks again so much!
smeeb
CC BY-SA 3.0
2015-06-12T15:07:08.913Z
@smeeb The name, to be honest, I'm not quite sure!  It seems that it's technically [Radiant exposure](https://en.wikipedia.org/wiki/Radiant_exposure) but I haven't heard that phrase used in an atmospheric context...
gerrit
CC BY-SA 3.0
2015-06-12T15:08:36.027Z
@smeeb The ranges are way different because one is *per day*, and the other is *per year*.  This is an integrated quantity, i.e. the total amount of energy received per unit area per day vs. per year.  1000 per year is on average less than 3 per day (but the comparison is not fair because the US map is per day in a summer month whereas the Swedish one is for an entire year)
gerrit
CC BY-SA 3.0
2015-06-12T15:58:17.940Z
@smeeb just an aside, but "pitch black" means no photons in the visible wavelengths, but there may be energy in any other part of the spectrum.  [Solar irradiance](https://en.wikipedia.org/wiki/Solar_irradiance) works well as a proxy of brightness because peak solar emission is in the visible spectrum.
casey
CC BY-SA 3.0
2015-06-12T15:00:56.797Z
2017-03-02T08:49:02.977Z
2017-03-02T08:49:02.977Z
gerrit
<p>It occurred to me that there might very will be a metric out there that measures and quantifies "daily brightness". Meaning, how bright any given day is, taking weather conditions and cloud coverage into account.</p>

<p>A general brightness metric is <strong>lumens</strong>, but I can't find anything on this subject with respect to meteorology.</p>

<p>And, if such a metric does exist, what's its range, 0 - 100? What weather/ambient conditions are represented at this range's extrema?</p>

<meteorology><measurements><clouds><light>
How can daily brightness be quantified or measured?
smeeb
# How can daily brightness be quantified or measured?

(Asked by: username_0 on 2015-06-12)

It occurred to me that there might very will be a metric out there that measures and quantifies "daily brightness". Meaning, how bright any given day is, taking weather conditions and cloud coverage into account.

A general brightness metric is **lumens**, but I can't find anything on this subject with respect to meteorology.

And, if such a metric does exist, what's its range, 0 - 100? What weather/ambient conditions are represented at this range's extrema?

**Tags:** meteorology, measurements, clouds, light


---

## 2 answers

### Answer by username_2 on 2015-06-12. Score: 8 | Accepted answer

It can be measured in units of energy per surface area, for example, **kWh/m2**. The official SI name would be [radiant exposure](https://en.wikipedia.org/wiki/Radiant_exposure) but I haven't seen that phrase used in a climate or weather context.

For example, here is a map by NREL of average radiation per *day* in the US for July:

![NREL map of radiation in the USA](https://i.sstatic.net/vCvbN.jpg)
  
(Source: [National Renewable Energy Laboratory](http://www.nrel.gov/gis/solar.html))

And here is a map for Sweden for the same quantity per *year* (hence the much larger numbers):

![SMHI map of radiation in Sweden](https://i.sstatic.net/fSWaY.png)
  
(Source: [SMHI](http://www.smhi.se/klimatdata/meteorologi/stralning/normal-globalstralning-under-ett-ar-1.2927))

> **Comments:**
> **username_0**: Thanlks @username_2 (+1) - very interesting! So what's the name of this type of metric, is it just "*solar radiation*? Or something else? Also can I assume that `0 kwH/m^2` is pitch black (no radiation/light whatsoever)? Thanks again!  
> **username_0**: Also, the ranges/scales on that unit are way different between to the two maps you show. For the American one, the range is between 2 and 9. For the Swedish one, they are between 700 and 1,100! Any thoughts there? Thanks again so much!  
> **username_2**: @username_0 The name, to be honest, I'm not quite sure!  It seems that it's technically [Radiant exposure](https://en.wikipedia.org/wiki/Radiant_exposure) but I haven't heard that phrase used in an atmospheric context...  
> **username_2**: @username_0 The ranges are way different because one is *per day*, and the other is *per year*.  This is an integrated quantity, i.e. the total amount of energy received per unit area per day vs. per year.  1000 per year is on average less than 3 per day (but the comparison is not fair because the US map is per day in a summer month whereas the Swedish one is for an entire year)  
> **username_4**: @username_0 just an aside, but "pitch black" means no photons in the visible wavelengths, but there may be energy in any other part of the spectrum.  [Solar irradiance](https://en.wikipedia.org/wiki/Solar_irradiance) works well as a proxy of brightness because peak solar emission is in the visible spectrum.  
> **username_3**: Pyranometers are the typical instrument for recording insolation [incoming solar radiation] that is integrated to make the figures above.  A great place to see this data in action is the Oklahoma Mesonet, such as http://www.mesonet.org/index.php/weather/meteogram/ (bottom plot)  Clouds will greatly reduce the values, but other times they will often be slightly below maximum values simply due to atmospheric composition, things like haze and pollution\stagnation, even temperature has some bearing.  

---

### Answer by username_1 on 2015-06-13. Score: 4

In addition to radiant exposure, for certain locations, some meteorological services record hours of sunlight for periods during each day when the [solar radiance](http://www.bom.gov.au/climate/austmaps/solar-radiation-glossary.shtml#radiationunits) equals or exceeds ${120\ \rm{W/m^2}}$. The weather observations for Sydney airport, for June 2015 can be seen [here](http://www.bom.gov.au/climate/dwo/IDCJDW2125.latest.shtml). Column 7 lists the sunlight hours for each day listed.

In terms of measuring data from the electromagnetic spectrum, ultraviolet radiation levels are measured, but not levels of light visible to the human eye.

In Australia, the Bureau of Meteorology measures the hours of sunshine each day but the [Australian Radiation Protection and Nuclear Safety Authority](http://www.arpansa.gov.au/uvindex/index.cfm) measures and records ultraviolet radiation levels.

Real time measurements for 11 locations are posted on this [site](http://www.arpansa.gov.au/uvindex/realtime/index.cfm).

This is snap shot of the data for Alice Springs. The yellow/orange line is the forecast UV and the pale blue line shows the measurements.

![enter image description here](https://i.sstatic.net/GKw2C.gif)


---

