NVG Conditions Planner

⚠ PLANNING AID ONLY — This tool provides estimates based on astronomical models and weather forecasts. All NVG operations must be conducted in accordance with your organisation's SOPs and relevant aircrew orders. Not for use as sole basis for operational decisions.

Location Selection

NPAS / Coastguard Base

Search City / Town

Latitude (°)

Longitude (°)

Forecast Window

Urban Light Pollution

Sun Altitude

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Moon Altitude

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Moon Phase

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Cloud Cover

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Urban Skyglow

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Location

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Key Times (Local)

Sunrise

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Sunset

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Civil Dusk

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Nautical Dusk

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Nautical Dawn

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Civil Dawn

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Moonrise

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Moonset

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Illuminance Timeline

Total illuminance

Excellent NVG ≥200 mlx

Good NVG ≥50 mlx

Marginal NVG 10 mlx

■ Night period

14-Day NVG Outlook

Run the Assessment first to set your location, then build the planner. Shows key astronomical data and a predicted NVG condition rating for best night conditions each day.

NVG Conditions Reference

NVG Score — What it means

The NVG Score (0–10) is this tool's single-number assessment of how well night vision goggles are likely to perform in current conditions. It combines ambient illuminance, cloud cover, moon phase, and local light pollution into a single operational rating.

Score	Rating	What to expect
8 – 10	Excellent	Near-full moon, clear skies. Excellent situational awareness. Terrain and obstacles clearly defined. Scene detail good.
6 – 8	Good	Useful moonlight available. Good scene recognition. Most tasks achievable with normal crew workload.
4 – 6	Moderate	Reduced lunar illumination or partial cloud. Usable NVG performance but crew workload increases. Careful low-level work.
2 – 4	Poor	Low ambient light. NVGs functional but performance degraded. High crew workload. Limit to essential tasks.
0 – 2	Marginal	Near-darkness. NVG performance severely limited. Scene recognition very difficult. Operations should be approached with extreme caution.

Illuminance Thresholds

Ambient illuminance (measured in millilux, mlx) is the primary driver of NVG performance. These thresholds are approximate guides:

Illuminance	Typical source	NVG effect
≥200 mlx	Full moon, clear sky	Excellent. Near-photopic equivalent through goggles.
50–200 mlx	Half moon or cloudy full moon	Good. Clear terrain features and scene recognition.
10–50 mlx	Quarter moon / thin cloud	Usable. Reduced contrast and depth cues.
<10 mlx	Starlight / overcast	Marginal to unusable. Very limited scene recognition.

How the Model Works

This tool combines several sources of illumination:

Moonlight — Calculated from the moon's altitude above the horizon, its illuminated fraction (phase), and the real-time cloud cover forecast. Moonlight peaks at ~250 mlx for a full moon directly overhead in clear conditions.
Twilight — A smooth, continuous model of how sky brightness fades as the sun descends below the horizon. Civil twilight (−6°) typically provides 1,000–3,000 mlx; nautical twilight (−12°) provides 1–50 mlx; below −18° (astronomical night), the sun's contribution is effectively zero.
Urban skyglow — Light pollution from towns and cities adds a baseline illuminance floor. This actually aids NVG performance over urban areas but degrades scene contrast. The model estimates this from settlement population.
Cloud cover — Live forecast from Open-Meteo (updated hourly). Cloud attenuates moonlight sharply but scatters urban skyglow back down, partially offsetting the loss in city environments.

Note: This model does not account for precipitation, fog, mist, smoke, or volcanic ash — all of which can further degrade NVG performance significantly. Always check full meteorological data.

Twilight Definitions

Civil twilight — Sun between 0° and −6°. Bright sky. NVGs typically not required.
Nautical twilight — Sun between −6° and −12°. Sky dimming rapidly. NVG transition zone.
Astronomical twilight — Sun between −12° and −18°. Dark sky. NVGs typically required for low-level work.
Night — Sun below −18°. True night. NVG performance determined by moon and cloud.