How bright is moonlight compared to sunlight?

A full moon is roughly 400,000 times dimmer than direct sun, about 18 to 19 stops less light. That is why a sunny day exposes near EV 15 while a full-moon landscape sits around EV minus 3 to minus 4 at the ground.

What is the Looney 11 rule?

It is the night-time cousin of the Sunny 16 rule. For a detailed, well-exposed full moon disc, set aperture to f/11 and shutter to 1 over the ISO. This tool generalises that idea to whole moonlit landscapes, not just the lunar disc.

Why does moon altitude matter?

Light from a low moon passes through far more atmosphere, dimming and reddening it. A moon near the horizon delivers roughly a stop less usable light than one overhead, so the calculator reduces the scene EV as altitude drops.

How does phase change the exposure?

Brightness scales with the illuminated fraction, but not linearly. A half moon gives far less than half a full moon's light because of shadowing on its surface. The model drops about one stop per major phase step, so plan on a few extra stops away from full.

Can I photograph the moon's surface with these settings?

No. The bright lunar disc needs Looney 11 settings (f/11, 1 over ISO) or it blows out. These landscape settings are for the dim ground lit by the moon, which is many stops darker than the disc itself.

What is the Lunar Phase & Moonlight Exposure Calculator?

Estimate the exposure value of moonlight from lunar phase percentage and moon altitude, then derive shutter speed, aperture, and ISO for moonlit landscapes and astrophotography. Includes a Looney 11 style brightness model. Runs entirely in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Lunar Phase & Moonlight Exposure Calculator

Name: Lunar Phase & Moonlight Exposure Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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This calculator estimates how much light the moon throws on a scene and turns that into practical camera settings for moonlit landscapes and wide-field astrophotography. It models scene brightness from the moon’s illuminated fraction and its altitude above the horizon.

How it works

Exposure is anchored in EV at ISO 100. A full moon high in a clear sky lights the ground at roughly EV -3 at ISO 100 — about 18 stops below the Sunny-16 daylight value of EV 15.

Two corrections adjust that baseline:

Phase. Brightness falls faster than the illuminated fraction because of shadowing across the lunar surface. The model subtracts stops as you move away from full, using log2(fraction) scaled so a half moon is roughly three stops dimmer than a full moon.
Altitude. A low moon shines through more atmosphere. The model removes up to about one stop as altitude drops toward the horizon, and none when the moon is overhead.

The resulting scene EV is converted to a shutter time using the canonical relationship:

2^EV = (aperture^2) / shutter_seconds      at ISO 100

scaled for your chosen ISO. Solving for shutter gives:

shutter = (aperture^2) / (2^EV) * (100 / ISO)

Worked example

Full moon (100% illuminated) high overhead, shooting at f/2.8, ISO 1600:

Scene EV at ISO 100 is about -3.
shutter = 2.8^2 / 2^(-3) * (100 / 1600) = 7.84 * 8 * 0.0625 ≈ 3.9 s.

So a roughly 4-second exposure at f/2.8, ISO 1600 gives a balanced moonlit landscape — short enough to keep stars near pinpoints with a wide lens.

Notes

Snow, water, and pale sand reflect far more moonlight; reduce exposure a stop. Dense forest or dark rock needs a stop more.
The moon’s disc is many stops brighter than the moonlit ground. To capture surface detail use Looney 11 (f/11, shutter = 1/ISO) instead.
Treat the result as a starting point and bracket. Everything runs locally in your browser.