# OliNo

Renewable Energy

## Spectrum of moon light

Posted by Marcel van der Steen in Explanation
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When I was looking for a spectrum of moonlight, I could not find it on the internet. As I do a lot of lamp measurements myself (see the category lamp measurements), I decided to measure the moon spectrum myself and put that info available on the internet.

### Measurement circumstances

The measurement has been done on 14th of April 2014. It was an evening with few clouds and we had a full moon, well visible. Taking measurements with the spectrometer SpecBos 1211 can then be done in two ways.

1) measurement of the illuminance (in lux). However the expected illuminance is only 1 lux and that results in a very faint spectrum with signals for each wavelength too close to the noise limit to have a nice signal.

2) measurement of luminance (in Cd/mˆ2), and that requires a very well alignment of the measurement device in the direction of the moon, as the sensitivity area of the device in this mode is only two degrees wide.

I mounted the spectrometer on a tripod and kept on aligning and measuring until I had an output with a high signal.

### Measurement results

Here the spectrum and derived parameters.

Lastly an csv-file with the measurement data, which is an average of 24 measurements.

And here the file extended with a column for Ee (in W/m^2/nm) and the approximated illuminance value (in lux). An illuminance value of 0.14 lux is what would be expected.

### 53 Responses to “Spectrum of moon light”

1. Ur-1el Says:

Great job. I was very helpful. I want to thank you very much. Can I repay you somehow?

2. George Felix Says:

Great work, I’m thinking of doing my PhD on the cooling effects of the moonlight.

Do you have the Latitude and Longitude of the experiment location?

If I understand correctly, the experiment was done on a full moon. Have you run the experiment on a new moon (Black No Moon) in order to compare the results between the two?

3. mvdsteen Says:

Dear George. I measured the moon from my address. In the measurement file you can find the time and date. The address coordinates are: latitude: 51.42359906, longitude: 5.40894538. I did not redo the measurement at other moon cycles. It was already hard enough to get a nice measurement with the full moon (I had to point it very precisely as the spectrometer had to be in radiance mode and has then only an acceptance window of 1.8 degrees).
You can use the data, my info is found here: http://www.olino.org/us/contributors/marcel-van-der-steen

4. Richard Davis Says:

Marcel…
This is very well done, original observation. It’s very much appreciated.

Do you have any ideas about what might be causing the notch in the lunar light spectrum at about 760 nm? That is an interesting spot on the wavelength line because many IR filters have that as a pass band. I’m hoping there is something to pass.

5. mvdsteen Says:

Richard, it seems to me the absorption effect of O2, see also this image from Wiki.

6. Anne Leugers, PhD Says:

Richard- Thank you! Nice work! I’m looking at suppression of melatonin by light and have been told by 1 researcher that we don’t need to worry about moonlight because it contains little to no radiation in the 460nm-480nm range. Your nice ground-based data refutes that.

7. Anne Leugers Says:

mvdsteen- just a thought.. did you calibrate your integrating sphere first with white light standard and color standard to ensure wavelength and amplitude accuracy? Thanks!

8. mvdsteen Says:

Anne, I do agree there is energy in the wavelength range between 460-480 nm. However that amount of energy is very little. If I were to measure it in illuminance, then hat would be probably less than 1 lux. I am not sure whether such small amounts of energy would do anything.

About the calibration: the spectrometer I used is calibrated by the supplier every year. He does the calibration on wavelength and also on absolute energy level.

Thanks so much Marcel.
This is actually the only spectral data for moonlight that I could find.
I am trying to compare the spectral differences between sunlight and moonlight. Accounting for the flux differences and instrumentation differences would you have the spectrum information for sunlight around the same day that you collected this moonlight data?
Much appreciated!

10. mvdsteen Says:

Dear Prahallad. I also could not find any moon spectral data on the internet which is why I measured it. Now I had to measure in luminance mode, since in illuminance mode the signal would be too small. I measured 177 cd/m^2 in luminance mode, while the sensitive field of view for the spectrometer was 1.8 degrees (angular diameter). This corresponds to only 7.8E-4 sr. Assuming to measure illuminance, and also assuming only the moon to be a bright object, I would only have measured 0.14 lux (meaning the 177 cd/m^2 = 177 lm/sr/m^2 and as I have measured this over only 7.8E-4 sr, I multiply the 177 x 7.8E-4 and get 0.14 lm/m^2 is 0.14 lux). This is very small and would require a 60 seconds measurement time and 60 seconds dark measurement time. The resulting spectrum would be slightly higher than noise level of the meter.
Now for the sun, I did not measure the sun with the specbos 1211. First, there is a lot of that spectrum to be found on the internet. Second, I cannot measure the sun with the specbos 1211 in luminance mode, since that would directly yield an overexposure. And even in the illuminance mode I would not be able to measure the sun with my specbos 1211 since it can only measure up to 10000 lux and the sun will go much higher than that.
So I am sorry, I do not have the sun’s spectrum for you.

11. Owen Says:

While I agree there isn’t much benefit to obtaining yet another spectrum of the sun (plenty are out there), spectral features are distinguishable looking at the light of (brightly) illuminated surfaces. Obviously this should have some impact,varying based on setup, but as a first approximation you can get reasonable results in large bands without having to look at the sun directly with equipment that can’t manage.

12. Guido Grimaldi Says:

Dear Marcel, thank you very much!
You had an excellent initiative. In fact, we can not find spectral data from the moon on the internet and academic journals. Thanks, I really need to check this out. I am thinking of doing more for my PhD measures like these. I want to compare the spectral data of the moonlight on a new moon and full moon. I thought of taking the measurements by attaching a telescope to the spectrophotometer, what do you think? Maybe the signal increases, no?
Thank you for helping!

13. Marcel van der Steen Says:

Dear Guido, if you are going to use a spectrometer (you need it in order to get a full spectrum), then I found that you will need a luminance mode, that way the sensor is much more sensitive and also it is sensitive only in one small field angle. Mine has a angular diameter of 1.8 deg=31 mrad, whereas the moo has an angular diameter of 9 mrad, so it is possible to fit the moon inside the angle of view of my spectrometer. The advantage is high sensitivity and that only in a very small field.
Would you use a spectrometer with cosine sensitive head, you will need to amplification. The telescope will be of help. Only that the telescope should be able to pass all wavelengths where you are interested in. I expect that the glass will absorb the UV.

14. Guido Grimaldi Says:

Oh great! Thanks Marcel, very useful. I really don’t think about the absorption of UV light on the telescope glass. I’m interested in all wavelengths possible, but i think that for my objective study the more important is the spectral beetwen UV and Royayl Blue (360-460nm). But alright I can try make this with telescope might right. I’ll come back here when new questions come up, okay? See you!

15. Dr. Karolina M. Zielinska-Dabkowska Says:

Dear All,
For those who are looking for spectrum of daylight
Here my paper published in Nature Journal with measurements:
https://www.nature.com/articles/d41586-018-00568-7

16. John Says:

Dr. Zielinska-Dabkowska that is a fascinating article. Do you have any specific recommendations for schools?

17. Martin Says:

Thank you, very helpful data. I would like to compare this light spectrum with a light spectrum of a white light LED that I measured and which I adjusted to an intensity that should be in the range of moonlight. My measurements are spectral irradiance measurments and are given in [W/(sqm*nm)]. To compare this two spectra I need to convert radiance [W/(sr*sqm*nm)] into irradiance [W/(sqm*nm)].
Could anyone give me advise on how to do that? Thank you!

18. Marcel van der Steen Says:

@Martin, I have added a file where there is an additional column with Ee [W/m^2/nm]. This is I think what you asked for. For a sanity check I calculated the illuminance value from that column and it resulted in a value of 1.34 lux, which seems reasonable to me.

19. Martin Zurl Says:

Dear Marcel, thank you very much for your help! That was exactly what I was looking for. When I compare your spectrum with my white light LED measurement, it falls in a range that I would have expected based on the lux values of the spectra.

20. Marcel van der Steen Says:

Well done, I see now that I mistakenly said 1.34 lux but it is 0.134 lux. Which is as expected. Glad you can go forward with the results.

21. John Smoak Says:

Can anybody tell me if the light frequency changes based on the phase of the moon?

With new work showing how our brains respond to yellow vs blue light, I am curious.

22. Curiosity Says:

Recently I saw some info in the internet that the moon is self illuminating and that moonlight is different from sunlight. Can anyone tell me: from the light spectrum obtained, does it show that the moonlight is actually different from sunlight?

Please forget about the moon reflects the sun that we have been taught in textbook.

23. John Says:

The Sun’s diameter changes with wavelength, the effective diameter at 21cm is approximately 1.8 degrees whilst at visible wavelengths it is approximately 0.5 degrees.
Does the diameter of the Moon change with wavelength or does its far lower temperature preclude this?

24. robert p Says:

Dear Marcel
This may be of tangent a bit, but I am building a saltwater reef aquarium and have been following a few people talking about the effects of moonlight on reef systems. There is a body of thought that suggests the moonlight is beneficial to the reef system and that it can be replicated with lighting at night over the tank. That being said, what color spectrum lamp/bulb/led would most replicate natural moonlight? [what would you recommend?]

25. Rajdeep singh Says:

I was curious about it about 30 minutes ago. after searching a while i came here and i learned a lot from this. thank you so much for providing it to us.

26. Gary Nicholls Says:

We see from recent images from the Chang’e 4 mission on the lunar far side that the Suns position WRT the observer makes a great difference to the colour and brightness of the lunar surface, but we see no observable difference in the Moons colour from Earth.(except during eclipse) Also the images from the orbiting telescopes show a purple lunar far side, as can be seen here:
http://lilacsat.hit.edu.cn/dashboard/pages_en/pics-b.html
Little is known about the camera so I would suspect callibration, but the colour of the lunar surface in many images taken from the near side surface during the Apollo missions also show great variations in colour.
It would be very interesting to run your experiments using the same setup from outside of Earths atmosphere, from a high orbit or cislunar space, but that would be very expensive. Very interesting, and good work Marcel.

27. Dorian Leger Says:

Thanks Marcel! I used the excel with Ee and found a big drop in Irradiance surrounding 517 nm.

~517 nm does not correspond to atmospheric absorption or solar spectra, so could that be surface material on the moon?

Any guess what it is?

28. Dorian Leger Says:

Oh excel was playing its usual tricks on me. The drops are actually at 762nm and 938nm, which I guess are O2 and H2O signals.

29. Juan Alvear Says:

Thanks!
I was looking for the data, and you are the only source.

I’m sure NASA knows, but it must be too hard to find.

Frequencies tell a lot about material composition

Thanks

30. Lauri Lehtiaho Says:

Expect hits by Flat Earthers. They think moonlight is cooling, unlike sunlight, and it gives it’s own light instead of reflecting that of the Sun.

31. Tim Says:

Dr KM Z-D.

You state early on that researchers are worried that artificial lights are thought to be responsible for changing sleeping patterns from 2 x 4 hrs of sleeping plus 1 hr of wakefulness to 1 x 8 hrs.
Surely this should be the other way around?

ie uninterrupted sleep is better than interrupted sleep.

32. Tim Says:

John – she is surely saying that natural light is what we were designed for, so ideally school lighting should reflect this fact; ie blue components are fine during the day, but should be changed towards the red-orange end of the spectrum as evening approaches.
So daylight should be encouraged as the primary lighting source – ie big windows, etc.

Hello, I am trying to research the altitude that the moon must be or order to have its light penetrate the surface on full moon as well as when it is 25% full (quarter full) in the sea where the waters are clear and free of debris/ sediment.

If you have more informations on how I can find out at what altitude the moon must be from the horizon in order to penetrate down to the bottom in clear waters, white sandy sea floor and an average depth of 5-8 feet.

Kind Regards,

34. Trent W Nichols Jr MD Says:

The problem with using spectroscopy on earth to measure moonlight is “the fact that Earth’s atmosphere gets in the way; Some wavelengths of light get absorbed in our planet’s atmosphere in unpredictable ways, skewing scientists’ measutements,” and is the reason a flying telescope was used to capture the most accurate measurements ever or the brightness of moonlight!

Amateur Astronomer and physician scientist in biophysics

Reference: Moon Brightness Mystery Prompts Launch of Airborne Telescope

35. James Reeves Says:

The dips are most likely do to water vapor. Water in other forms, liquid, etc. also absorbs in same general region, but if you had a high resolution spectrometer you would see lots of sharp bands for vapor and a broad band for liquid.

One way to somewhat show vapor effects would be to take spectrum at low and high humidity (winter, summer?).

You might also try using a solar spectrum obtained from space and seeing where differences occur. Water absorbs more and more strongly as one goes from UV to the midIR (out to 25,000 nm).

Nice work, just some ideas?

Jim Reeves

P.S.
Problem with web is that a lot of info is available in tech journals which is hard to find and costly to obtain unless your employer pays for it. Neither titles nor abstracts will indicate a water spectrum in an article on medical uses of spectroscopy, for example.

36. Mamma Mia Says:

Great work. I’m looking at spectrum of moonlight compared to sunlight. Your data shows a greater proportion of red wavelengths compared to sunlight. Do you know why this is? Can you suggest possible reasons? Thanks!

37. Mike Says:

In France, where I live, plenty of people believe that the fading of their curtains is primarily caused by moonlight. Yes, it’s what they’ve heard and believe. I try to tell them that moonlight is far, far weaker than sunlight and that, for all I know, it contains, proportionally, even less ultraviolet light than sunlight as I assume not all wavelengths reflect the same.
What is the fact? How much weaker is overall moonlight and how many times smaller is the ultraviolet component?

38. mvdsteen Says:

@Mike, moonlight won’t harm your curtains, just because as you say, the light intensity is soo much smaller than that of direct sunlight. The sun’s spectrum is found in many places on the internet. Just not the moon’s spectrum and that is why I have measured it.
Now I mentioned in the article that the illuminance is about 1 lux. Compare this to a 50.000 – 100.000 lux when measuring the direct sunlight. This means that the intensity is roughly 50.000 times smaller than that of sunlight. So even if the UV and blue components reflecting via the moon are relatively as strong as the other wavelengths, it’s intensity will be 50.000 times smaller. This could not pose any harm to your curtains.
Look it this this way: do you ever tan when bathing in moonlight? I am sure you will not. Then also your curtains will not bleach due to it.

39. Leo Says:

Nice spectral measurement, Marcel. A very helpful endeavour, no doubt, given the lack of spectral data for moonlight out there on the web.
I´d like to ask at what altitude did your measurement take place, since altitude (actually, the amount of atmosphere between the moon and ourselves) can heavily influence the perceived spectrum.
I know the measurement process is complicated, but maybe it would be interesting to compare the luminance of the moon at different altitudes.
I´d love you to read any thoughts from you on this regard.
Thanks for the time you´ve dedicated to this so far.
Regards.

40. Leo Says:

Nice spectral measurement, Marcel. A very helpful endeavour, no doubt, given the lack of spectral data for moonlight out there on the web.
I´d like to ask at what altitude did your measurement take place, since altitude (actually, the amount of atmosphere between the moon and ourselves) can heavily influence the perceived spectrum.
I know the measurement process is complicated, but maybe it would be interesting to compare the luminance of the moon at different altitudes.
I´d love you to read any thoughts from you on this regard.
Thanks for the time you´ve dedicated to this so far.
Regards.

41. mvdsteen Says:

@Leo, altidude was 4.5 m above ground level in Veldhoven, The Netherlands. I was making the measurements on the first floor.

42. Alex Says:

Very nice work! The amount of atmosphere between the moon and instrument depend also on the zenith angle of the moon. What its value?
Kind Regards

43. Sajesh Vijayan Says:

Hi Marcel, Can I use this spectrum, more specfically the extended file having the Ee values, on a peer-reviewed article? If so, can I have your credentials for citing you appropriately? The link in the reply thread above seems to be broken. Thanks so much.

44. mvdsteen Says:

@Sajesh, that is fine with me. Refer to mvdsteen @ http://www.olino.org

45. Joe Says:

Hello there,
I just made my first astronomical spectroscopy of the moon today. Could i show your spectra as comparison to mine on my youtube ?

I would refer to “mvdsteen @ http://www.olino.org“, if that’s okay with you.

Best wishes, j

46. Mvdsteen Says:

@Joe, that is OK. Did you find big differences?

47. Joe Says:

Thanks a lot!
My spectrometer is a diy project portable 5″ TFT screen with Hamamatsu’s C12880 spectrometer. It only has 288 channels and the spectral resolution is around 8 nm. So it looks less detailed. I did not save the measurement and only filmed my screen, because i had to hold a lens with both hands to focus the light. I will give it another try, so i can compare both values in a spreadsheet. I still have to calibrate the incoming light flux of all channels. I’ll keep you up to date.

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