Reflector Hood
A shaped metal housing that redirects bulb light toward the plant canopy.
Reflector hoods redirect light that would otherwise be wasted—useful for HID bulbs that emit in all directions. But they don't add light; they only redistribute what's already there. For modern LEDs with built-in optics, an external reflector is redundant and won't improve performance. Reflector quality does matter: material, finish, and shape affect how evenly light hits your canopy.
Definition
A reflector hood is a shaped metal housing that surrounds a HID light and redirects light that would otherwise escape upward or sideways back down toward the plant canopy. Because HID bulbs—including High-Pressure Sodium, Metal Halide, and Ceramic Metal Halide—emit light in roughly 360°, a reflector recaptures photons that would be lost.
Common designs include:
- Wing reflector: flat or gently angled panels that direct light downward and outward
- Parabolic: a deep, bowl-shaped reflector that concentrates light toward the center
- Air-cooled hood: an enclosed glass-bottomed housing with duct flanges for heat removal via inline fans
How it works
A reflector hood increases the fraction of lamp output that reaches the canopy and shapes the light pattern to match the grow footprint. The hood's material, surface finish, and geometry determine how much light is recaptured and how evenly it is distributed.
Reflectivity varies by material and finish. Specular (mirror-finish) aluminum typically reflects 85–95% of visible-range photons under laboratory conditions, while white-painted surfaces achieve 80–90% but produce a more diffuse spread. Weak / limited[1] These ranges depend heavily on surface preparation, age, and wavelength—reflectance in the far-red and infrared spectrum used by plants can differ from visible values. Weak / limited[2]
Importantly, a reflector hood does not increase the bulb's total output. It only redirects existing photons. Claims that a hood "adds 30% more light" typically mean it delivers ~30% more photosynthetically useful light to the canopy compared to a bare bulb or inferior reflector, not that the bulb is producing more energy. Weak / limited[3]
What it doesn't do
A reflector hood is designed for HID bulbs and is not reliably beneficial for modern LED grow lights. LEDs with built-in lens optics or directional phosphors already control light distribution; adding an external reflector may create unwanted hot spots or uneven coverage rather than improvement. No data
A reflector hood also does not mitigate light burn or heat stress on its own. Air-cooled hoods equipped with duct flanges allow growers to pull heat away from the bulb via an inline fan—a practical advantage for HPS bulbs—but this system does not eliminate the need to manage canopy temperature and light intensity based on plant response and ambient conditions.
Practical use
Air-cooled hoods are the main reason reflectors remain common in commercial HPS setups. By enclosing the bulb in glass and ducting cool air around it, growers can run high-intensity lamps closer to plants than passive (open) reflectors allow, thereby increasing light delivery without overheating the leaves.
Maintenance matters: Reflective surfaces degrade over time as aluminum oxidizes and dust accumulates. Cleaning hoods between growing cycles helps maintain efficiency; badly corroded reflectors lose reflectivity significantly over months or years. Weak / limited
Reflector geometry affects evenness: Deep parabolic and bowl-shaped reflectors often create bright central hot spots with dimmer edges, while wing-style hoods tend to produce more uniform coverage, especially in small or tent-style grow spaces. Grower preference depends on canopy size and layout.
Replacing a corroded or low-quality stamped-metal hood with a better reflector may improve light distribution, but this alone does not guarantee higher yield—improved light delivery must be paired with appropriate nutrient, CO₂, and other environmental conditions.
Comparison with modern LED fixtures
Modern LED grow lights incorporate reflective optics or lensed diodes during manufacture, so external reflector hoods are generally unnecessary and may reduce performance by interfering with designed light paths. Early-generation LEDs were sometimes paired with external reflectors, but this practice has largely been abandoned. If you are using a commercial LED fixture, the manufacturer's instructions will specify whether external reflectors are recommended—most current designs do not.
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.
- Reported U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy (2021). Energy Savings Potential of Solid-State Lighting in Horticultural Applications.
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Related
- HID Lights — Gas-discharge lamps that produce high light intensity; standard in older indoor grows, now...
- Reflectors for HPS Lights — Hoods that redirect HPS bulb output downward for better canopy light distribution.