Solar Curve Visualizer.
Solar Curve Visualizer
What the sun does, hour by hour, at any latitude on any date — elevation and clear-sky PPFD.
Why this matters
Solar Replication is one of OAT's distinguishing capabilities. The same engine that drives this visualizer drives lighting fixtures in indoor and greenhouse contexts to mimic natural sun for any latitude on any date — letting you grow tropical strawberries in Iceland by mimicking Costa Rica's light, or run a Costa Rica winter day in Tucson if that's the climate your cultivar needs.
For greenhouse operators, knowing the natural PPFD curve tells you exactly when supplemental lighting is needed and how much. For outdoor growers, it tells you what your plants are actually receiving. For indoor growers wanting to mimic natural rhythms, it shows what nature looks like in the climate you want to replicate.
What you're seeing
The chart above shows two curves across a 24-hour day:
- Solar elevation (green): the angle of the sun above the horizon. 0° at sunrise/sunset; peaks at solar noon. Higher elevation means more direct light and shorter atmospheric path.
- PPFD (amber): the photosynthetically active photon flux density at ground level under clear-sky conditions. This is what plants experience without cloud cover.
Solar time is shown on the x-axis. Solar noon is when the sun is at its highest point — typically very close to (but not exactly) clock noon, depending on time zone offset and equation of time.
The math
Solar elevation is computed from latitude, declination (which depends on day of year), and hour angle:
elevation = arcsin(sin(latitude) × sin(δ) + cos(latitude) × cos(δ) × cos(ω)) where: δ = solar declination (varies with day of year) ω = hour angle = 15° × (solar_hour − 12)
Clear-sky PPFD is approximated using a simplified atmospheric model that accounts for air mass (atmospheric path length increases at lower sun angles, reducing intensity):
air_mass = 1 / sin(elevation) direct_PAR ≈ 2150 × sin(elevation) × 0.7^(air_mass^0.678) diffuse_PAR ≈ 220 × sin(elevation) PPFD ≈ direct_PAR + diffuse_PAR
Real sky conditions vary substantially. Clouds reduce PPFD anywhere from 30% (light overcast) to 90% (heavy storm). Pollution, dust, and aerosols also reduce intensity. The clear-sky model is the upper bound; actual delivered PPFD is typically 60-90% of this on average days.
Solar Replication mode
For OAT customers running indoor or greenhouse cultivation with tunable LED fixtures, the same math drives the Light Engine's Solar Replication mode. You can:
- Faithfully replicate your local sun for educational or research-grade biology
- Substitute climates — grow Brazilian Sungold in Norway by mimicking Brazil's sun
- Spoof latitude — give equatorial 12/12 to a temperate grower's plants for stable photoperiod
- Spoof seasons — run June 21 conditions in February for off-season cultivation
- Compress or expand time — run a 24-hour solar arc in 18 hours, or stretch to 26 (research / experimentation)
- Replay successful seasons — recreate the actual June 21, 2024 sun for an heirloom variety that did particularly well that year
Most ag-lighting software does on-off scheduling and dimming. Solar Replication is what advanced research labs build custom — and what OAT makes standard.
References
Solar position math from standard astronomy (NOAA Solar Calculator, Spencer 1971 Fourier-series approximation, Astronomical Almanac). Clear-sky PPFD model is a simplification of the Bird Clear Sky Model (Bird & Hulstrom 1981); for research-grade work, use Bird directly or the SOLPOS / SMARTS implementations from NREL.
Free under CC BY 4.0. Cite as "OAT Solar Curve Visualizer (openagriculturetechnology.com)".