# Thread: How many lux or lumens is the Sun?

1. ## How many lux or lumens is the Sun?

Just wondering.

Anyone knows?

2. ## Re: How many lux or lumens is the Sun?

Easy

Once we know how bright the sun is in lux directly overhead, we can use that number to figure the lumens (since the sun radiates more or less equally in all directions.

Digging around, I found that bright sunlight is 50K-100K lux. Let's go halvies on that, and say 75K lux.

Now, lux is defined as lumens per square meter. So, we are measuring 75,000 lumens per square meter at the Earth's surface. All we have to do is find the number of square meters on the surface of a sphere with a radius equal to the Earth's distance from the sun.

The Earth is about 150 million km from the sun (150 billion meters). The formula for the area of a sphere of radius r is 4(pi)r^2.

Thus, the sphere has a surface area of 4(pi)(150x10^9)^2 = 2.83*10^23 square meters.

Multiply that by the lux value from before (75,000 lux = 75,000 lumens/m^2) and we get 2.12x10^28 lumens.

4. ## Re: How many lux or lumens is the Sun?

LOL!

OK. How about lumens at the surface of the sun!!!

5. ## Re: How many lux or lumens is the Sun?

Easy enough...

The sun's diameter is 1.4 million km, so the radius is 700,000 KM (or 700 million meters). Taking the above formula for surface of a sphere, and the sun's surface area is 6.2x10^18 meters.

Dividing the above luminous output by the surface area gives 3.4 billion lumens per square meter.

6. ## Re: How many lux or lumens is the Sun?

... and still not taking into account the losses in earth's atmosphere ... [img]/ubbthreads/images/graemlins/grin.gif[/img]

7. ## Re: How many lux or lumens is the Sun?

For those who don't know... lol

2.12x10^28 lumens

this is scientific notation... [img]/ubbthreads/images/graemlins/smile.gif[/img] an easier way to express really large or really small numbers..

8. ## Re: How many lux or lumens is the Sun?

[ QUOTE ]
Negeltu said:
For those who don't know... lol

2.12x10^28 lumens

this is scientific notation... [img]/ubbthreads/images/graemlins/smile.gif[/img] an easier way to express really large or really small numbers..

[/ QUOTE ]

2.12x10^28 lumens aka 21,200,000,000,000,000,000,000,000,000 lumens! [img]/ubbthreads/images/graemlins/faint.gif[/img]

9. ## Re: How many lux or lumens is the Sun?

[ QUOTE ]
Kiessling said:
... and still not taking into account the losses in earth's atmosphere ... [img]/ubbthreads/images/graemlins/grin.gif[/img]

[/ QUOTE ]

True - how much loss would you say it accounts for? I'm sure that my calculation is well within one order of magnitude.

10. ## Re: How many lux or lumens is the Sun?

anyway, it is pretty impressing, this little yellow thing that hangs in the sky... [img]/ubbthreads/images/graemlins/smile.gif[/img] ... a fusion lamp ...
bernhard

11. ## Re: How many lux or lumens is the Sun?

[ QUOTE ]
evan9162 said:
[ QUOTE ]
Kiessling said:
... and still not taking into account the losses in earth's atmosphere ... [img]/ubbthreads/images/graemlins/grin.gif[/img]

[/ QUOTE ]

True - how much loss would you say it accounts for? I'm sure that my calculation is well within one order of magnitude.

[/ QUOTE ]
I would say *well* within an order of magnitude. I have a referance that addresses the atmospheric absorbtion question. As you would expect, it varies a bit across the spectrum but it appears that the incoming flux is about 55% higher above the atmosphere than at sea level with the sun overhead.

13. ## Re: How many lux or lumens is the Sun?

Thanks for the info, Doug.

So taking into account atmospheric losses, we can round and say around 3x10^28 lumens.

14. ## Re: How many lux or lumens is the Sun?

Zero Lux, but only at night!

15. ## Re: How many lux or lumens is the Sun?

[ QUOTE ]
Doug S said:
[ QUOTE ]
evan9162 said:
[ QUOTE ]
Kiessling said:
... and still not taking into account the losses in earth's atmosphere ... [img]/ubbthreads/images/graemlins/grin.gif[/img]

[/ QUOTE ]

True - how much loss would you say it accounts for? I'm sure that my calculation is well within one order of magnitude.

[/ QUOTE ]
I would say *well* within an order of magnitude. I have a referance that addresses the atmospheric absorbtion question. As you would expect, it varies a bit across the spectrum but it appears that the incoming flux is about 55% higher above the atmosphere than at sea level with the sun overhead.

[/ QUOTE ]

As I recall from some photoelectric work, at sea level, when the sun is directly overhead, you get about 1 kilowatt per square meter of irradiation. In space, as far away from the sun as earth orbits you get about 1.7KW. So 55% is certainly close enough. Obviously, this varies with clouds, smoke, smog, fog, dust, humidity and don't forget ALTITUDE.

16. ## Re: How many lux or lumens is the Sun?

To get an accurate lumen value, one would have to construct an integrating sphere in space around the sun (a Dyson sphere with a pure flat white interior), taking into account the planets and other objects in orbit around the sun. Until that happens though, one would have to extrapolate the lumen value based upon a very small area of flat illuminated surface from a known distance from the sun.

17. ## Re: How many lux or lumens is the Sun?

[ QUOTE ]
ESD said:
As I recall from some photoelectric work, at sea level, when the sun is directly overhead, you get about 1 kilowatt per square meter of irradiation. In space, as far away from the sun as earth orbits you get about 1.7KW. So 55% is certainly close enough. Obviously, this varies with clouds, smoke, smog, fog, dust, humidity and don't forget ALTITUDE.

[/ QUOTE ]
I believe that your 1KW and 1.7KW figures apply to total solar radiation. Since the original question was about lux and lumens which apply only to light, not total radiation, I looked at only the 400-700nm portion of the solar spectrum to get that 55% figure.

18. ## Re: How many lux or lumens is the Sun?

For the Lux measurement, you want to know the value about which distance? At one meter [img]/ubbthreads/images/graemlins/grinser2.gif[/img]

19. ## Re: How many lux or lumens is the Sun?

[ QUOTE ]
evan9162 said:

Easy

Once we know how bright the sun is in lux directly overhead, we can use that number to figure the lumens (since the sun radiates more or less equally in all directions.

Digging around, I found that bright sunlight is 50K-100K lux. Let's go halvies on that, and say 75K lux.

Now, lux is defined as lumens per square meter. So, we are measuring 75,000 lumens per square meter at the Earth's surface. All we have to do is find the number of square meters on the surface of a sphere with a radius equal to the Earth's distance from the sun.

The Earth is about 150 million km from the sun (150 billion meters). The formula for the area of a sphere of radius r is 4(pi)r^2.

Thus, the sphere has a surface area of 4(pi)(150x10^9)^2 = 2.83*10^23 square meters.

Multiply that by the lux value from before (75,000 lux = 75,000 lumens/m^2) and we get 2.12x10^28 lumens.

[/ QUOTE ]

Yes....but,

Digging around some more, for what is more applicable to us down on earth, and more specifically how we rate incident light from the flashlights we use, for comparison; noon daylight reaching the surface of the earth at the equator(relatively constant throughout the year), after being filtered by the atmosphere we get around only 10,000-12,000 fc(lumens/f-sq'd) and full moon only about 0.02 fc. So turning your Aurora or simliar very high output lights, and shining directly into your eye's is like looking at the sun, you'll go blind!

Keep these 'toys', like a loaded gun, away from children.

Units of measure HTML(usual number of formatting errors in conversion) [img]/ubbthreads/images/graemlins/eek.gif[/img]

20. ## how many lumens does the sun put out???

so how many lumens does the sun put out?
any way to calculate that?

21. ## Re: how many lumens does the sun put out???

that should be relatively easy.......just pop it into an integrating sphere

22. ## Re: how many lumens does the sun put out???

Lumens isn't everything. Reliability has to be considered also. The sun only shines in the daytime, when you don't need it.

By the way shouldn't we be using candle power, not lumens, in this forum?

23. ## Re: how many lumens does the sun put out???

Working backwards a little, the sun's total output without the earth's atmosphere in the way is about 1350 W/m². About half that is visible light, and the luminous efficacy of the solar spectrum is about 199 lm/W, so we get roughly 135,000 lumens/m². At the distance of the earth's orbit this energy falls on an imaginary sphere with a radius of 150 million kilometers, or 1.5 x 10^11 meters. The surface area of this sphere is 4*pi*r², or 2.827 x 10^23. Multiplying this by 135,000 lumens per m² gives us 3.816 x10^28 lumens, or put another way 38,160 trillion trillion lumens. Of course, this is an approximation, but it gives you some idea of the order of magnitude we're talking about here.

I heard the next release from Luxeon is going to have a similar output.

24. ## Re: how many lumens does the sun put out???

Originally Posted by jtr1962
or put another way 38,160 trillion trillion lumens. Of course, this is an approximation, but it gives you some idea of the order of magnitude we're talking about here.
I would have expected much higher.

25. ## Re: how many lumens does the sun put out???

So jtr1962 what your really saying is just a bit less than my NLS huh

26. ## Re: how many lumens does the sun put out???

Originally Posted by LuxLuthor
I would have expected much higher.
Really?? 38,160,000,000,000,000,000,000,000,000 Lumens

That is a lot of lumens!

jtr1962, great post man!! You really know your Science, thats impressive.

27. ## Re: how many lumens does the sun put out???

Originally Posted by jtr1962
Working backwards a little, the sun's total output without the earth's atmosphere in the way is about 1350 W/m². About half that is visible light, and the luminous efficacy of the solar spectrum is about 199 lm/W, so we get roughly 135,000 lumens/m². At the distance of the earth's orbit this energy falls on an imaginary sphere with a radius of 150 million kilometers, or 1.5 x 10^11 meters. The surface area of this sphere is 4*pi*r², or 2.827 x 10^23. Multiplying this by 135,000 lumens per m² gives us 3.816 x10^28 lumens, or put another way 38,160 trillion trillion lumens. Of course, this is an approximation, but it gives you some idea of the order of magnitude we're talking about here.

I heard the next release from Luxeon is going to have a similar output.
So if you used 100 lumen Luxeon III's you would need 3.8 x 10^26 of them. I don't know their weight but let's guess 1 gram. So that would be 3.8 x 10^23 kg of luxeons.

According to google the earth's mass is about 6x10^24 kg (= 60 x 10^23). So you only need 6.3% of the mass of the earth in Luxeon's to match the sun's output. The heatsinking and power supply might be a deal-breaker though

Greg

28. ## Re: how many lumens does the sun put out???

If a pinhead sized piece of the sun's core could be placed here on earth—well we can't get within ninety (90) miles of it. That HOT! and That BRIGHT!

29. ## Re: how many lumens does the sun put out???

thanks jtr1962 i suspect you have some kind of engineering degree to know all that physics

30. ## Re: how many lumens does the sun put out???

38,160 trillion trillion lumens? If it is indeed written like PSM had it, that'd be 38 octillion, 160 septillion lumens!

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