Lighting
49 Barrina fixtures, 1,446W, $0.161/hour. The lights fill two shadow windows: morning (east tree blocks until 10:30 AM) and late afternoon (sun drops below effective transmission angle).
Electric cost, kilowatt-hours, and solar alignment percentage. The lights are the second-largest electric consumer after the fog machine. On a winter day with 12 hours of supplemental lighting, that’s $1.93 — a meaningful portion of the daily budget but necessary for adequate DLI.
When the Lights Run
On/off timeline for both circuits. The pattern reveals the two shadow windows: lights ON in early morning (tree blocks east-facing sun until 10:30 AM), OFF during midday solar peak, then back ON in late afternoon as transmission angle drops. Cloudy days show extended runtime — the lux threshold triggers supplemental light whenever indoor readings drop below 3,000 lux.
Daily Runtime
Hours per day of grow light operation. Winter: 10–12 hours. Summer solstice: 4–6 hours. The seasonal curve mirrors day length inversely — longer natural light means less supplemental need. But even in June, the morning tree shadow guarantees at least a few hours of grow light runtime.
DLI Budget
Left: DLI accumulation through the day — watch it climb in steps (natural light) and plateaus (cloudy periods or tree shadow). Right: daily DLI totals against the 14 mol/m²/d target. Grow lights contribute an estimated 8–12 mol/m²/d. Combined with corrected natural light (12–17 mol), total plant DLI is likely 20–29 mol — excellent for all planned crops.
Natural Light Estimates
Left: estimated natural DLI based on outdoor lux × glazing transmission model. Right: real-time estimated indoor PPFD (green) overlaid with outdoor lux (yellow). The ratio between them is the glazing’s effective transmission at that moment — varying from 6.9% when the sun is behind the east tree to 23.5% when it hits the southwest face at the optimal angle.
The Hex Shape Signature
Effective glazing transmission varies throughout the day as the sun traverses the hexagonal structure. The opal polycarbonate (Gallina PoliCarb 2P, 6mm twin-wall) transmits 57% of light at perpendicular incidence, but real-world transmission depends entirely on the angle between sun and wall face. Southwest face at 210–240° azimuth: 23.5%. East face behind the tree: 6.9%. This hex-shaped transmission curve is unique to this greenhouse’s geometry and orientation.
Indoor/Outdoor Lux
Indoor lux (from the Kincony LDR on GPIO35) vs outdoor lux (Tempest weather station) with solar altitude overlay. The indoor sensor is severely flawed — saturates at ~28,000 lux, misses morning hours (tree shadow), can’t see grow lights. The outdoor sensor provides the ground truth; the glazing model estimates the rest.
Two Circuits
”Grow” Circuit — 34× 2FT Fixtures (816W)
Direct, close-range light over hydro rails and shelf positions. Barrina 2FT T8 LED, 24W, 96 LEDs, CRI 80, 12” on center.
| Location | Count | Watts |
|---|---|---|
| Hydro top row | 7 | 168W |
| Hydro bottom row | 7 | 168W |
| East wall shelves (seedlings) | 5 | 120W |
| West wall shelves | 15 | 360W |
”Main” Circuit — 15× 4FT Fixtures (630W)
Ambient overhead light from west wall rafters. Barrina 4FT T8 LED, 42W, 192 LEDs, CRI 98, 36” on center.
Both circuits controlled via Lutron switches → Home Assistant → ESP32 HTTP API. Automation parameters: lux threshold 3,000, DLI target 14 mol/m²/d, window 7 AM–7 PM. The 3,000 lux threshold happens to correlate with the tree shadow clearing the sensor position — effectively open-loop until a proper BH1750 digital sensor replaces the LDR.
→ See Climate Overview for the full light environment analysis and corrected DLI estimates. → See Cooling for how solar radiation drives both light and heat — the same energy that grows plants also overheats the greenhouse.