<p>Perhaps you may be interested in downward shortwave flux? It isn't easy to compute or measure, but it should capture what you are after. You can use the equation <span class="math-container">$$R_{net}=S\downarrow-S\uparrow+L\downarrow-L\uparrow$$</span></p>
<p>where <span class="math-container">$S$</span> represents shortwave, <span class="math-container">$L$</span> represents longwave, <span class="math-container">$R_{net}$</span> is the net radiation, and the arrows depict upward or downward. If you assume an albedo <span class="math-container">$\alpha$</span>, you can say that <span class="math-container">$S\uparrow$</span> is a fraction of <span class="math-container">$S\downarrow$</span>: <span class="math-container">$$R_{net}=S\downarrow(1-\alpha)+L\downarrow-L\uparrow$$</span></p>
<p>If you use an IR thermometer, you can measure the temperature of the sky (<span class="math-container">$T_{sky}$</span>) and the ground (<span class="math-container">$T_{ground}$</span>). If you assume a corresponding emissivity (\epsilon), then you can invoke Stefan-Boltzmann's &quot;law&quot; and get <span class="math-container">$$R_{net}=S\downarrow(1-\alpha)+\sigma\left(\epsilon_{sky}T_{sky}^4-\epsilon_{surface}T_{surface}^4\right)$$</span>.</p>
<p>If you measure <span class="math-container">$R_{net}$</span> using a net radiometer, you can solve for <span class="math-container">$S\downarrow$</span>. Alternatively, you can also compute <span class="math-container">$S\downarrow$</span> empirically, like some of the climate models do. But that is perhaps the most computationally intensive part of climate modeling.</p>

CC BY-SA 4.0
2022-09-27T16:01:13.077Z
2022-09-27T16:01:13.077Z
BarocliniCplusplus
<blockquote>
<p>I am looking for a meteorological measure of daylight brightness/luminosity...but is there a measure that also captures the fact that particular regions of the world, far from the equator, have not only less daylight at some point during the year, but also less brightness, or luminosity, meaning that the sun is further down or up in the sky.</p>
</blockquote>
<p>Consider the following -</p>
<p>Radio Corporation of America, 1968 (and in later years), RCA Electro-Optics Handbook. Section 6.  Sources of Radiation, p.6-10ff, fig. 6-10, Atmospheric Transmittance.</p>
<p>Note: The image (below) is from a republication by RCA ca. 1974, p 74.  Please note the original source reference, Bond and Henderson, 1963, given below.</p>
<p><a href="https://i.sstatic.net/hmvqg.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/hmvqg.jpg" alt="illuminance, due to sun, moon, &amp; sky, at surface of the earth." /></a></p>
<ol start="16">
<li>Bond, D.S. and Henderson, F.P., THE CONQUEST OF DARKNESS, AD 346297,
Defense Documentation Center, Alexandria, Va., 1963.</li>
</ol>

CC BY-SA 4.0
2022-09-27T05:11:54.110Z
2022-09-27T05:11:54.110Z
Thomas Perry
<p>I am looking for a meteorological measure of daylight brightness/luminosity. I can only find measures that are defined by the number of hours of sunlight during a day, but is there a measure that also captures the fact that particular regions of the world, far from the equator, have not only less daylight at some point during the year, but also less brightness, or luminosity, meaning that the sun is further down or up in the sky.</p>
<p>Maybe something close to a measure of <a href="https://en.wikipedia.org/wiki/Albedo" rel="nofollow noreferrer">albedo</a> at certain points in time and place?</p>

CC BY-SA 4.0
2022-09-26T11:30:08.883Z
The term you are looking for is "airmass", not to be confused with the meteorological concept of "air mass". [Does this answer your question](https://en.wikipedia.org/wiki/Air_mass_(astronomy))?
David Hammen
CC BY-SA 4.0
2022-09-26T14:29:48.447Z
I think this is it indeed, but then are there any systematic measures of this around the world? I mean like one would easily get access to data about the number of hours of sunlight in a given city, is it reasonable to think this is possible to get this for air mass as well?
Maël
CC BY-SA 4.0
2022-09-26T19:06:21.257Z
While albedo is a calculation of the reflection of solar radiation (percentage units), could you use the base measurement of incoming [solar radiation](https://en.wikipedia.org/wiki/Solar_irradiance) that is used in the albedo calculation? Its units are watts/square meter so it should take into account sun distance and angle. So it's about how much energy is coming in, not how much is being reflected back out.
Wxboyajm
CC BY-SA 4.0
2022-09-30T10:30:23.267Z
I now realize this might be duplicate of https://earthscience.stackexchange.com/questions/4987/how-can-daily-brightness-be-quantified-or-measured
Maël
<meteorology><sun>
Measure of daylight brightness
Maël
# Measure of daylight brightness

(Asked by: username_0 on 2022-09-26)

I am looking for a meteorological measure of daylight brightness/luminosity. I can only find measures that are defined by the number of hours of sunlight during a day, but is there a measure that also captures the fact that particular regions of the world, far from the equator, have not only less daylight at some point during the year, but also less brightness, or luminosity, meaning that the sun is further down or up in the sky.

Maybe something close to a measure of [albedo](https://en.wikipedia.org/wiki/Albedo) at certain points in time and place?

**Tags:** meteorology, sun

> **Comments:**
> **username_1**: The term you are looking for is "airmass", not to be confused with the meteorological concept of "air mass". [Does this answer your question](https://en.wikipedia.org/wiki/Air_mass_(astronomy))?  
> **username_0**: I think this is it indeed, but then are there any systematic measures of this around the world? I mean like one would easily get access to data about the number of hours of sunlight in a given city, is it reasonable to think this is possible to get this for air mass as well?  
> **username_2**: While albedo is a calculation of the reflection of solar radiation (percentage units), could you use the base measurement of incoming [solar radiation](https://en.wikipedia.org/wiki/Solar_irradiance) that is used in the albedo calculation? Its units are watts/square meter so it should take into account sun distance and angle. So it's about how much energy is coming in, not how much is being reflected back out.  
> **username_0**: I now realize this might be duplicate of https://earthscience.stackexchange.com/questions/4987/how-can-daily-brightness-be-quantified-or-measured  

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## 2 answers

### Answer by username_3 on 2022-09-27. Score: 1

Perhaps you may be interested in downward shortwave flux? It isn't easy to compute or measure, but it should capture what you are after. You can use the equation $$R\_{net}=S\downarrow-S\uparrow+L\downarrow-L\uparrow$$

where $S$ represents shortwave, $L$ represents longwave, $R\_{net}$ is the net radiation, and the arrows depict upward or downward. If you assume an albedo $\alpha$, you can say that $S\uparrow$ is a fraction of $S\downarrow$: $$R\_{net}=S\downarrow(1-\alpha)+L\downarrow-L\uparrow$$

If you use an IR thermometer, you can measure the temperature of the sky ($T\_{sky}$) and the ground ($T\_{ground}$). If you assume a corresponding emissivity (\epsilon), then you can invoke Stefan-Boltzmann's "law" and get $$R\_{net}=S\downarrow(1-\alpha)+\sigma\left(\epsilon\_{sky}T\_{sky}^4-\epsilon\_{surface}T\_{surface}^4\right)$$.

If you measure $R\_{net}$ using a net radiometer, you can solve for $S\downarrow$. Alternatively, you can also compute $S\downarrow$ empirically, like some of the climate models do. But that is perhaps the most computationally intensive part of climate modeling.


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### Answer by username_4 on 2022-09-27. Score: 0

> I am looking for a meteorological measure of daylight brightness/luminosity...but is there a measure that also captures the fact that particular regions of the world, far from the equator, have not only less daylight at some point during the year, but also less brightness, or luminosity, meaning that the sun is further down or up in the sky.

Consider the following -

Radio Corporation of America, 1968 (and in later years), RCA Electro-Optics Handbook. Section 6. Sources of Radiation, p.6-10ff, fig. 6-10, Atmospheric Transmittance.

Note: The image (below) is from a republication by RCA ca. 1974, p 74. Please note the original source reference, Bond and Henderson, 1963, given below.

[![illuminance, due to sun, moon, & sky, at surface of the earth.](https://i.sstatic.net/hmvqg.jpg)](https://i.sstatic.net/hmvqg.jpg)

16. Bond, D.S. and Henderson, F.P., THE CONQUEST OF DARKNESS, AD 346297,
    Defense Documentation Center, Alexandria, Va., 1963.


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