How bright is moonlight? The full moon in lux, explained

A full moon high in a clear sky lights the ground with about 0.05 to 0.3 lux, and usually toward the low end. That is roughly 400,000 times fainter than direct sunlight and hundreds of times dimmer than a lamp-lit living room. It is still bright enough to walk by, because your eyes switch to their most sensitive cells, and a full moon gives about ten times as much light as a half moon, thanks to a quirk of the lunar surface.

Step outside on a clear full moon night, away from streetlights, and you barely need a flashlight. You see the path, the fence, the outline of the trees and your own shadow beside you. This article covers how bright moonlight really is in numbers you can compare, why you can walk by it but lose your colors, how a surface as dark as asphalt can shine so brightly, what a supermoon changes, and when moonlight peaks and fades in 2027.

How bright is the full moon in lux?

Light falling on a surface is measured in lux. For years, research papers quoted full moon values anywhere from 0.5 to more than 2 lux. In 2017 the researchers Christopher Kyba, Andrej Mohar and Thomas Posch set the record straight in the journal Astronomy & Geophysics. During the supermoon of November 14, 2016, they measured 0.26 lux in an open field near Vienna, with the Moon 55.5 degrees above the horizon. With the Moon directly overhead it would have been close to 0.3 lux. That is the ceiling, and it only happens in the tropics, because the Moon never passes straight overhead from latitudes above about 28 degrees. At temperate latitudes, typical full moonlight is more like 0.05 to 0.1 lux.

A ladder from dark to bright puts that in perspective:

• Moonless, overcast night: 0.0001 lux
• Quarter moon on a clear night: about 0.01 lux
• Full moon on a clear night: 0.05 to 0.3 lux
• Public areas with dark surroundings: 20 to 50 lux
• Living room lights: about 50 lux
• Office lighting: 320 to 500 lux
• Overcast day: about 1,000 lux
• Direct sunlight: 32,000 to 100,000 lux

So the strongest moonlight on Earth falls in places like southern India, the Philippines and northern Australia, where a full moon can stand nearly overhead. And everywhere, a single living room lamp beats the full moon hundreds of times over. That you can walk by moonlight at all says less about the Moon than about your eyes.

Why can you see by moonlight but not see colors?

Your retina has two kinds of light-sensitive cells. About 4.6 million cones handle daylight and color. About 92 million rods are far more sensitive but see no color at all. As the light fades, the cones drop out and the rods take over. That switch takes time: rod sensitivity improves a lot in the first 5 to 10 minutes of darkness and keeps improving for half an hour or more. Every glance at a bright phone screen sets you back.

Full moonlight sits right at the border. There is enough light for your rods to pick out shape, movement and contrast, but not enough for your cones to show proper color. The lawn turns gray, a red car looks black, and the whole landscape goes silver.

There is a further twist, named after the Czech anatomist Jan Evangelista Purkyně, who described it in 1819. Rods are most sensitive to blue-green light, around 498 nanometers, and almost blind to deep red. In dim light, reds fade to black first while blues and greens hold on. That is why moonlight feels cool and silvery, even though its spectrum is actually slightly redder than daylight.

Can you read by moonlight?

Big headlines, yes, once your eyes have adapted. Ordinary book print is a struggle for most people. Sharp detail vision depends on the cones, and full moonlight is close to the lowest level at which cones work at all. The same logic explains the red lights in aircraft cockpits and submarine control rooms: red light lets the cones read instruments while leaving the rods’ night vision largely intact.

If the Moon is as dark as asphalt, why is it so bright?

Here is the surprise: the Moon is not a white ball. Its surface reflects only about 12% of the sunlight that hits it, an albedo of about 0.12, comparable to worn asphalt. Put a piece of the Moon next to an old road in the sunshine and you would struggle to tell them apart.

It looks brilliant for three reasons. It sits in full, unfiltered sunlight, and 12% of that is still a lot. It hangs against a black sky, and your eyes judge brightness by contrast. And there is the opposition surge.

The lunar surface is rough: dust, grit, pebbles, craters. When sunlight strikes it at an angle, as it does at half moon, every grain casts a tiny shadow on its neighbor, and billions of little shadows dull the surface. At full moon the sunlight comes from almost exactly behind you, so you look at every grain from the direction the light arrives, and each grain hides its own shadow behind itself. The shadows vanish together and the surface jumps in brightness. Measurements show the Moon brightening by more than 40% in just the last 4 degrees of its approach to exact full.

A full moon has only twice the lit area of a half moon, yet it gives about ten times as much light, because at full moon every grain of lunar dust hides its own shadow.

So a full moon is not twice as bright as a half moon, as the lit area would suggest, but about ten times as bright: roughly 0.01 lux at quarter moon against about 0.1 lux at full. It also explains why the Moon can look perfectly round a night away from full, yet noticeably fainter.

Is a supermoon brighter?

Yes, measurably. Moonlight falls off with the square of the distance, and the Moon’s distance at full moon swings between roughly 357,000 and 406,000 kilometers. NASA puts the difference at up to 14% bigger and 30% brighter for the closest full moon of a year compared with the faintest.

2027 shows the extremes neatly. The Wolf Moon of January 22 is the closest full moon of the year at 357,635 km, the headline supermoon of 2027. The Buck Moon of July 18 (July 19 in Australia) is the farthest at 405,968 km, a micromoon. Run the numbers and the January Moon is about 13.5% wider and gives about 29% more light.

Can your eyes see that? Barely, because there is no second Moon beside it to compare. Height matters even more. The light landing on flat ground scales with how high the Moon stands, so a full moon 60 degrees up lights the ground about 70% more than one 30 degrees up. With a camera on fixed settings, though, the supermoon difference shows clearly. See how to photograph the Moon with your phone.

Can you see a rainbow by moonlight?

Yes, and it is one of the rarest sights moonlight offers. A moonbow forms like a rainbow, with moonlight instead of sunlight shining into water drops. It needs a moon at or near full, low in the sky (below 42 degrees), a dark sky, and rain or spray on the side of the sky opposite the Moon. Because the light is so faint, a moonbow usually looks white to the eye, and the colors only appear in a long-exposure photo.

Waterfalls with constant spray are famous for them, including Cumberland Falls in Kentucky, Victoria Falls on the border of Zambia and Zimbabwe, and Yosemite in California. Elsewhere it takes luck: a shower in the evening or before dawn with a low, bright full moon at your back. Bright moonlight also produces the pale ring described in ring around the moon.

Moonlight carries meaning beyond optics, too. In India, on Sharad Purnima, the full moon of the Hindu month of Ashvin, many families leave a bowl of kheer out overnight under the moonlight, in the belief that the rays carry amrita. It is one of the dates in holidays set by the moon.

When is moonlight brightest in 2027?

Three things decide how much moonlight reaches the ground: how close the Moon is, how high it climbs and how long it stays up. A full moon rides high in winter and low in summer, so the two hemispheres swap their best nights.

• Brightest: the Wolf Moon, January 22 (12:17 UTC). The closest full moon of 2027, high in the northern winter sky and up all night. On fresh snow, expect sharp shadows and a landscape that seems lit from below.
• Longest moonlit night in the north: the Cold Moon, December 13 (December 14 in Australia). The highest full moon of the year in the northern sky, up through the longest nights. The flip side: the Geminids, the richest meteor shower of 2027 at about 150 per hour, peak on December 14 and will be largely washed out.
• Best in the south: the Strawberry Moon, June 19 in Australia, New Zealand and South Africa (June 18 in the US). The lowest full moon of the year for northern viewers is a high winter moon down south.
• Faintest: the Buck Moon, July 18. The farthest full moon of 2027, and in the northern hemisphere a low moon in short summer nights.

There is no total or partial lunar eclipse in 2027, only three penumbral ones, on February 20, July 18 and August 17 (dates in UTC), which show as a subtle dimming at most. Details are in eclipses in 2027. For the darkest skies, plan around new moon instead, and see the best nights for stargazing in 2027. All full moon dates and UTC times are in the 2027 full moon calendar, and if bright moonlight keeps you awake, read full moon and sleep.