# If the moon were a light bulb how many watts would it be.

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zdcyclops
If the moon were a light bulb how many watts would it be.

hyunxu
If the moon were a light bulb how many watts would it be.
More than 2.345E watts it may be.But still need to research because moon is non-luminous and glows with help of sunlight.

Homework Helper
If the moon were a light bulb how many watts would it be.
Average lunar albedo is 12%. Solar intensity is about 1050 W/m^2.
Lunar diameter is 3474 Km.
So: about 0.12 * 1.05 * pi * 3.474^2 *1,000,000 KW
That's excluding illumination from Earth.

Roughly 4.8 GW

hyunxu
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Average lunar albedo is 12%. Solar intensity is about 1050 W/m^2.
Lunar diameter is 3474 Km.
So: about 0.12 * 1.05 * pi * 3.474^2 *1,000,000 KW
That's excluding illumination from Earth.

Roughly 4.8 GW
I arrived at 1,200 TW with your calculation: ##0.12 \cdot \pi \cdot r^2 \cdot 1.05\, kWm^{-2}## with ##r=1,737,000 \,m##

But I haven't checked, whether the ##1,05 \,kWm^{-2}## fits to the 400 trillion trillion watts they've claimed here for the sun.

Mentor
If the moon were a light bulb how many watts would it be.
Do you mean the total effective luminous power of the Moon, or do you mean what size lightbulb would be the equivalent of the Moon's illumination through a window in your home at night?

https://www.coopersofstortford.co.uk/images/products/large/st09845i.jpg

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Staff Emeritus
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Going in the opposite direction, The illuminance of a full Moon on a clear night can be 0.3 lux or 0.3 lumen/m2
We are 384,000 km from the Moon, so that's 5.6e17 lumens total spread out over a the surface of a sphere with a radius equal to the Earth-Moon distance.
If we are going to treat this like a normal light bulb radiating in all directions, then this is would be the total Lumen output, but if we are only going to treat the Sunlit side of the Moon, we can divide this in half. (I'm ignoring any losses caused by the light passing through the atmosphere).

How much wattage this equates to for a light bulb depends on its efficiency. An incandescent bulb produces about 15 Lumens per watt, but an LED bulb typically produces 80 lumens per watt.

If you are talking about what would be the equivalent for a standard light bulb at typical distances, 0.3 lux is about as much light as you would get from a single 60 watt incandescent bulb at a distance of 14.6 meters or a 1/4 watt incandescent at a distance of 1 meter.

berkeman
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Going in the opposite direction, The illuminance of a full Moon on a clear night can be 0.3 lux or 0.3 lumen/m2
We are 384,000 km from the Moon, so that's 5.6e17 lumens total spread out over a the surface of a sphere with a radius equal to the Earth-Moon distance.
How much wattage this equates to for a light bulb depends on its efficiency. An incandescent bulb produces about 15 Lumens per watt, but an LED bulb typically produces 80 lumens per watt.
That makes ##37,300 \,TW## resp. ##7,000 \,TW##. The previous calculation with the albedo gave ##1,200 \,TW##. The gap is closing down. A factor between ##1## and ##30## seems acceptable considering the overall dimensions.

zdcyclops
Thanks for all of the replies. My question was poorly worded I'll try again. If I were on the moon and looked at my feet I would perceive a certain brightness. If i could shrink my self to the size of an ant and stand on a light bulb what wattage would the light need to be to produce the same perceived brightness.

Staff Emeritus
Gold Member
Thanks for all of the replies. My question was poorly worded I'll try again. If I were on the moon and looked at my feet I would perceive a certain brightness. If i could shrink my self to the size of an ant and stand on a light bulb what wattage would the light need to be to produce the same perceived brightness.
That entirely depends on the size and type of light bulb. A typical 60 watt bulb is ~3 cm in radius, and if perfectly circular have a surface area of 57.8 cm2 or 0.00578 m2
If 0.3 lumen/m2 is detected at the Earth-Moon distance, then surface of the Moon should be at 0.3 x (384,0000/1738)2 = 48816 lumens/m2. Which equals 282 lumens total over the surface of our bulb. This is works out to a 20 watt incandescent bulb. However, a 20 watt bulb is not likely to be as large as a 60 what bulb. which means a smaller surface area, and a lower total lumen output, which in turn means a lower wattage. An Appliance type bulb is ~2cm in radius, and at this size, the wattage would drop to ~8 watts. So in this case, we are looking at something about 1/2 as bright as a typical 15 watt appliance bulb.

Staff Emeritus
Thanks for all of the replies. My question was poorly worded I'll try again. If I were on the moon and looked at my feet I would perceive a certain brightness. If i could shrink my self to the size of an ant and stand on a light bulb what wattage would the light need to be to produce the same perceived brightness.

This makes zero sense. The moon is not a light source.

If you are asking about how much light is reflected off the moon's surface from the sun, than ask that! Otherwise, the answer is zero.

Zz.

davenn and PeroK
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If the moon were a light bulb how many watts would it be.

None, surely?

"There is no dark side of the moon. As a matter of fact, it's all dark!"

davenn
zdcyclops
You guys are waaayyy over thinking this. I am asking how bright is the surface of the moon and what size/power/wattage light bulb comes closest to that. I am curious because of all the Apollo hoaxers that use crap about shadows and how the bottoms of the lander is too bright. I want to be able to put it in the simplest terms possible i.e. If the moon were a x what light bulb how bright would the bottom of the lander be? Do you think you would be able to see the stars? And other silly questions.

Mentor
You guys are waaayyy over thinking this. I am asking how bright is the surface of the moon and what size/power/wattage light bulb comes closest to that. I am curious because of all the Apollo hoaxers that use crap about shadows and how the bottoms of the lander is too bright. I want to be able to put it in the simplest terms possible i.e. If the moon were a x what light bulb how bright would the bottom of the lander be? Do you think you would be able to see the stars? And other silly questions.
Ah, thanks for clarifying. We don't discuss or debunk nonsense here at the PF. Thread is done.

Mentor
It is reflected sunlight. Your question, even though you do not see it at the moment, wants to see the surface as a point source of light. It is not. Bulbs are small, the moon surface is not. If you stipulate an area, say 1m2, we can give you an answer using the average albedo (reflectance) of the surface.

The moon does not emit visible light like a light bulb.

russ_watters, davenn and PeroK