Library · Structures, greenhouse & energy
Greenhouse Light Transmission.
Greenhouse Light Transmission
How much sunlight actually reaches your canopy after passing through glazing, structure, and shade cloth? The number that determines whether you need supplemental lights.
Glazing comparison reference
| Material | PAR transmission | Insulation (R-value) | Lifespan |
|---|---|---|---|
| Single-layer float glass | 90-92% | ~0.9 | Decades |
| Diffuse glass (modern) | 90-94% | ~0.9 | Decades |
| Single poly film | 85-88% | ~0.8 | 3-4 years |
| Double poly film inflated | 75-80% | ~1.5 | 3-4 years |
| Polycarbonate twin-wall 8mm | 80-83% | ~1.5 | 10-15 years |
| Polycarbonate twin-wall 16mm | 74-78% | ~2.5 | 10-15 years |
| Polycarbonate triple-wall | 62-68% | ~3.0 | 10-15 years |
| Acrylic single | 86-90% | ~1.0 | Decades |
| Fiberglass corrugated | 65-75% | ~0.9 | 5-10 years; yellows |
Tradeoffs
- Higher transmission usually means lower insulation. Triple-wall polycarbonate cuts heating bills 30-50% but reduces winter light when you need it most.
- Diffuse glazing (frosted glass, light-spreading polycarbonate, light-diffusing poly) gives you better light distribution to lower canopy at small cost to total. For tall crops (tomato, cannabis) this is often net-positive.
- Light-diffusing films can be retrofit; roughly +5-15% canopy yield by reducing top-canopy "sunburn" and getting more to lower leaves.
- NIR-reflective glass (heat-reflective) keeps PAR while rejecting infrared — reduces summer cooling load at premium cost.
- Glazing maintenance is the easiest +10-20% light gain on most older greenhouses. Wash the inside, wash the outside, repair tears.
Free under CC BY 4.0. Cite as "OAT Greenhouse Light Transmission Calculator (openagriculturetechnology.com)".