HID Lights
High-intensity discharge lamps — the old workhorse of indoor cannabis cultivation, now being displaced by LED.
HID was the default for indoor cannabis from the 1980s through the 2010s, and plenty of growers still swear by it. The truth: modern LED fixtures now match or beat HPS on yield per watt, run cooler, and last longer. HID isn't dead — it's cheap upfront, simple, and proven — but the 'nothing grows weed like HPS' line is folklore at this point. If you're starting fresh in 2024, the math usually favors LED.
Definition
HID (high-intensity discharge) lights are gas-discharge lamps that produce light by striking an electric arc through ionized gas or metal vapor inside a sealed bulb. In cannabis cultivation the three relevant subtypes are:
- HPS (high-pressure sodium) — warm/amber spectrum, traditionally used for flowering.
- MH (metal halide) — cooler/bluer spectrum, traditionally used for vegetative growth.
- CMH / LEC (ceramic metal halide / light-emitting ceramic) — a newer ceramic-arc-tube variant with broader spectrum and better efficacy than standard MH [1].
What it does
HID lamps deliver high photosynthetic photon flux density (PPFD) over a wide canopy at relatively low fixture cost. A double-ended 1000W HPS produces roughly 1.7 μmol of photosynthetically active radiation per joule of electricity — competitive with mid-tier LEDs but below the best LED fixtures, which now exceed 2.7 μmol/J [1][2] Strong evidence.
HPS spectrum is heavy in yellow/orange/red and historically associated with strong flowering yields. CMH adds more blue and UV, which some growers credit for better trichome and terpene development, though controlled studies on cannabis specifically are limited Weak / limited.
What it doesn't do
HID does not inherently produce better cannabis than LED. The folk claim that 'HPS flowers denser buds' was true relative to early LEDs but no longer holds against modern high-efficacy fixtures Disputed. HID also runs hot — much of its input wattage becomes infrared/radiant heat — which raises HVAC load and can stress plants in warm rooms.
HID bulbs degrade: PAR output drops 10–20% over the first 5,000 hours and bulbs should be replaced every 1–2 grow cycles for HPS, longer for CMH [3].
Used in articles
See also: LED Grow Lights, PPFD, DLI (Daily Light Integral), Indoor Cultivation.
Sources
- 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.
- Peer-reviewed Kusuma, P., Pattison, P. M., & Bugbee, B. (2020). From physics to fixtures to food: current and potential LED efficacy. Horticulture Research, 7, 56.
- Government U.S. Department of Energy (2017). Energy Savings Potential of SSL in Horticultural Applications. DOE Solid-State Lighting Program. ↗
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