Reflector Hood
A reflective fixture that surrounds a grow light to redirect stray photons down onto the canopy.
A reflector hood is just a shaped piece of reflective metal around your bulb. It exists because bare bulbs throw light in every direction, including up at the ceiling where your plants aren't. A good hood meaningfully improves usable light on the canopy. A bad one creates hot spots and dim corners. The marketing around exotic geometries and proprietary coatings is mostly noise — what matters is reflectivity, shape, and whether it fits your space.
Definition
A reflector hood is a shaped metal housing that surrounds a grow lamp and redirects light that would otherwise escape upward or sideways back down toward the plant canopy. Hoods are standard equipment for high-intensity discharge (HID) lighting — including High-Pressure Sodium, Metal Halide, and Ceramic Metal Halide lamps — because the bulbs themselves emit light in roughly 360°.
Common shapes include the wing reflector (flat or gently angled panels), the parabolic (deep, bowl-shaped), and the air-cooled hood (an enclosed glass-bottomed housing with duct flanges for ventilation).
What it does
A reflector hood increases the share of lamp output that reaches the canopy and shapes the light footprint to match the grow area. Horticultural lighting references consistently show that fixture geometry and reflector material significantly affect photosynthetic photon flux density (PPFD) distribution at canopy height. Strong evidence [1][2]
Specular aluminum (mirror-finish) reflectors typically test at 85–95% reflectivity in the visible range, while white-painted surfaces sit around 80–90% but produce a more diffuse, even spread. Strong evidence [3]
What it doesn't do
A reflector hood does not increase the lamp's actual output — it only redirects existing photons. Claims that a particular hood "adds" 30% more light usually mean it delivers ~30% more usable light to the canopy compared to a bare bulb or a worse reflector, not that the bulb is producing more. Disputed
Hoods also do not meaningfully improve modern LED grow lights, which use lensed diodes or built-in optics to direct light without external reflectors. Bolting a hood onto an LED panel is generally pointless.
Practical notes
- Air-cooled hoods allow inline ducting to pull heat off the bulb, letting growers run HPS closer to the canopy without burning plants.
- Reflectivity degrades over time as aluminum oxidizes and dust accumulates. Wipe hoods between cycles.
- Hot spots under parabolic and deep-bowl reflectors are common; wing-style hoods typically produce more even coverage in small tents.
- Replacing a corroded or cheap stamped-aluminum hood with a quality specular unit is one of the cheapest yield upgrades in an HID room.
Sources
- Book Cervantes, J. (2006). Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible. Van Patten Publishing.
- Peer-reviewed Nelson, J. A., & Bugbee, B. (2014). Economic analysis of greenhouse lighting: light emitting diodes vs. high intensity discharge fixtures. PLoS ONE, 9(6), e99010.
- Government U.S. Department of Energy (2017). Energy Savings Potential of SSL in Horticultural Applications. DOE Solid-State Lighting Program. ↗
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