<p>There are four factors to consider.</p>
<ol>
<li>The moon is a lot less bright than the sun. Even at its brightest, the moon is only 1/400000 of brightness of the sun.  If you are trying to simulate this on a computer screen, give up now! No monitor has the ability to accurately represent the difference in brightness between a sunny day and a moonlit night.</li>
<li>The moon has phases, so has a smaller area than the sun. All other factors being equal (which they are not) a half moon would only be half as bright as a full moon.</li>
<li>When the moon is fully lit by the sun, at full moon, there is an effect called opposition-brightening. The moon when it is full is much more bright than two half-moons would be.</li>
<li>The moon has an elliptical orbit so its size, and brightness also vary as a result of its changing distance to the Earth.</li>
</ol>
<p>All these effects can be modelled, you can use the source code of (for example) Stellarium to see a fairly detailed model of the brightness of the moon.  It's not the sort of thing that can be accurately reduced to &quot;an equation&quot;.</p>
<p>This is before you apply atmospheric extinction, due to the effect of the atmosphere when the moon is low in the sky.</p>
<p>On top of this, you should consider the effect of low light levels on the rods and cones in your eyes.  In moonlit conditions, your &quot;cones&quot; (colour sensitive cells) are not active, so you see more or less in black and white.</p>
<p>So what do game designers do?  &quot;Accurately&quot; modelling moonlight is pointless, since the limitations of screens would mean that under moonlit conditions, the screen would be completely black.  Instead they reduce the brightness and saturation of colours to give the feel and effect of &quot;moonlight&quot; far more realistically than an &quot;accurate&quot; model would.</p>
<p>For a simple model, use the formula given at <a href="https://astronomy.stackexchange.com/questions/51505/calculate-moon-illumination-given-moon-age">Calculate moon illumination given moon age</a></p>

CC BY-SA 4.0
2024-10-27T20:36:58.167Z
Of course I won't simulate moonlight in a realistic way!!, I want to calculate it "comparison to its maximum intensity" so that the result is a percentage that I can control the maximum intensity I want according to my game which I'm developing.
Ahmed Dyaa
CC BY-SA 4.0
2024-11-01T22:26:35.243Z
Can I use the result of the [simple model](https://celestialprogramming.com/meeus-illuminated_fraction_of_the_moon.html) as an intensity value for a game engine light source? like at 2024/11/2 12:00 UTC+2 the Illumination value = 0.07%
Ahmed Dyaa
CC BY-SA 4.0
2024-11-01T22:44:03.727Z
You can.  But if your bright white under sunlight is #FFFFFF, then 0.07% of that rounds to #000000,  so the rendering is simple, everything is black.  But sure, go ahead and feed the numbers to your algorithm and see what it looks like.  I don't really understand rendering engines so I might be wrong or oversimplifying.
James K
CC BY-SA 4.0
2024-11-03T19:52:28.157Z
So the moon phase value like 0.07% meaning this is the percentage of sunlight reflected from the moon? Because I read that (The Moon's Bond albedo averages 0.136, meaning only 13.6% of incident sunlight is reflected from the lunar surface.)
Ahmed Dyaa
CC BY-SA 4.0
2024-11-03T21:27:03.037Z
That's something like the relative brightness of the sun and moon, It's related to both the albedo and the distance of the moon from the Earth (and the distance of the moon from the sun)
James K
CC BY-SA 4.0
2024-12-02T23:24:19.090Z
Do you have an Idea about how the lunar distance and moon altitude affect on the moonlight intensity?
Ahmed Dyaa
CC BY-SA 4.0
2024-12-03T04:23:19.120Z
Further is less bright (inverse square law), but the variation in brightness is not noticeable to most people.  Lower is also less bright, due to atmospheric extinction.
James K
CC BY-SA 4.0
2024-10-27T17:10:33.697Z
2024-10-28T06:56:48.057Z
2024-10-28T06:56:48.057Z
James K
<p>Is there an equation to accurately measure the intensity of moonlight using the lunar altitude like in this <a href="https://astronomy.stackexchange.com/questions/58584/the-intensity-of-sunlight">question</a> under natural conditions?</p>
<p>By &quot;under natural conditions&quot; I mean &quot;the moon is fully lit, there is no clouds and the location is in desert with and there is no other influences&quot;.</p>
<p>I want to calculate it &quot;comparison to its maximum intensity&quot; so that the result is a percentage that I can control the maximum intensity I want according to my game which I'm developing, Note that there is a game development engine (called Unity) parameter for the intensity of sunlight in Lux. It doesn't matter to be very precise; the important thing is to simulate it similar to the way the moon actually works.</p>

CC BY-SA 4.0
2024-10-27T16:55:51.293Z
"Measure" or "predict"  (I suspect, you mean "predict", since you can measure with a lightmeter)
James K
CC BY-SA 4.0
2024-10-28T06:57:03.863Z
https://astronomy.stackexchange.com/questions/51505/calculate-moon-illumination-given-moon-age might be a duplicate.
James K
CC BY-SA 4.0
2024-12-01T18:45:32.400Z
This question is similar to: [Calculate moon illumination given moon age](https://astronomy.stackexchange.com/questions/51505/calculate-moon-illumination-given-moon-age). If you believe it’s different, please [edit] the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem.
Mithoron
<the-moon><light>
The intensity of moonlight
Ahmed Dyaa
# The intensity of moonlight

(Asked by: username_0 on 2024-10-27)

Is there an equation to accurately measure the intensity of moonlight using the lunar altitude like in this [question](https://astronomy.stackexchange.com/questions/58584/the-intensity-of-sunlight) under natural conditions?

By "under natural conditions" I mean "the moon is fully lit, there is no clouds and the location is in desert with and there is no other influences".

I want to calculate it "comparison to its maximum intensity" so that the result is a percentage that I can control the maximum intensity I want according to my game which I'm developing, Note that there is a game development engine (called Unity) parameter for the intensity of sunlight in Lux. It doesn't matter to be very precise; the important thing is to simulate it similar to the way the moon actually works.

**Tags:** the-moon, light

> **Comments:**
> **username_1**: "Measure" or "predict"  (I suspect, you mean "predict", since you can measure with a lightmeter)  
> **username_1**: https://astronomy.stackexchange.com/questions/51505/calculate-moon-illumination-given-moon-age might be a duplicate.  
> **username_2**: This question is similar to: [Calculate moon illumination given moon age](https://astronomy.stackexchange.com/questions/51505/calculate-moon-illumination-given-moon-age). If you believe it’s different, please [edit] the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem.  

---

## 1 answers

### Answer by username_1 on 2024-10-27. Score: 1 | Accepted answer

There are four factors to consider.

1. The moon is a lot less bright than the sun. Even at its brightest, the moon is only 1/400000 of brightness of the sun. If you are trying to simulate this on a computer screen, give up now! No monitor has the ability to accurately represent the difference in brightness between a sunny day and a moonlit night.
2. The moon has phases, so has a smaller area than the sun. All other factors being equal (which they are not) a half moon would only be half as bright as a full moon.
3. When the moon is fully lit by the sun, at full moon, there is an effect called opposition-brightening. The moon when it is full is much more bright than two half-moons would be.
4. The moon has an elliptical orbit so its size, and brightness also vary as a result of its changing distance to the Earth.

All these effects can be modelled, you can use the source code of (for example) Stellarium to see a fairly detailed model of the brightness of the moon. It's not the sort of thing that can be accurately reduced to "an equation".

This is before you apply atmospheric extinction, due to the effect of the atmosphere when the moon is low in the sky.

On top of this, you should consider the effect of low light levels on the rods and cones in your eyes. In moonlit conditions, your "cones" (colour sensitive cells) are not active, so you see more or less in black and white.

So what do game designers do? "Accurately" modelling moonlight is pointless, since the limitations of screens would mean that under moonlit conditions, the screen would be completely black. Instead they reduce the brightness and saturation of colours to give the feel and effect of "moonlight" far more realistically than an "accurate" model would.

For a simple model, use the formula given at [Calculate moon illumination given moon age](https://astronomy.stackexchange.com/questions/51505/calculate-moon-illumination-given-moon-age)

> **Comments:**
> **username_0**: Of course I won't simulate moonlight in a realistic way!!, I want to calculate it "comparison to its maximum intensity" so that the result is a percentage that I can control the maximum intensity I want according to my game which I'm developing.  
> **username_0**: Can I use the result of the [simple model](https://celestialprogramming.com/meeus-illuminated_fraction_of_the_moon.html) as an intensity value for a game engine light source? like at 2024/11/2 12:00 UTC+2 the Illumination value = 0.07%  
> **username_1**: You can.  But if your bright white under sunlight is #FFFFFF, then 0.07% of that rounds to #000000,  so the rendering is simple, everything is black.  But sure, go ahead and feed the numbers to your algorithm and see what it looks like.  I don't really understand rendering engines so I might be wrong or oversimplifying.  
> **username_0**: So the moon phase value like 0.07% meaning this is the percentage of sunlight reflected from the moon? Because I read that (The Moon's Bond albedo averages 0.136, meaning only 13.6% of incident sunlight is reflected from the lunar surface.)  
> **username_1**: That's something like the relative brightness of the sun and moon, It's related to both the albedo and the distance of the moon from the Earth (and the distance of the moon from the sun)  
> **username_0**: Do you have an Idea about how the lunar distance and moon altitude affect on the moonlight intensity?  
> **username_1**: Further is less bright (inverse square law), but the variation in brightness is not noticeable to most people.  Lower is also less bright, due to atmospheric extinction.  

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