COB (Chip-On-Board)

COB (Chip-On-Board) LEDs were the dominant high-quality LED technology for cannabis lighting from approximately 2015-2019, before quantum board technology took over the premium grow light market. The technology: COB LEDs mount dozens to hundreds of individual LED chips directly onto a single ceramic or aluminum substrate (the "board"), with phosphor coating spread across the entire array creating a single concentrated light source. This contrasts with traditional surface-mount device (SMD) LEDs that mount each chip individually and quantum boards that spread chips across a larger flat panel. COB advantages (in the 2015-2019 era): concentrated point-source light (similar to incandescent or HPS bulbs in light pattern); easy to design simple fixtures with just a few COBs; consistent color rendering across the array; available in CRI 80+ and CRI 90+ versions for excellent plant color rendering; major brands like Citizen CLU048, Cree CXB3590, Bridgelux Vero series became the gold standard for DIY LED builders. COB cannabis fixture designs: typical setups used 4-12 COBs at 50-100W each, mounted on heatsinks with active or passive cooling; coverage area was 4-6 square feet per setup depending on COB count and wattage. COB disadvantages (which led to quantum board takeover): heat density at the COB chip is extreme, requiring active cooling for optimal performance and longevity; concentrated light pattern creates "hotspots" directly under each COB and shaded areas between them, requiring careful design and reflector use; efficiency plateau at around 2.2-2.5 µmol/J was lower than emerging quantum board technology; per-watt cost remained high vs quantum boards as production scale of small Samsung LM301 chips outpaced large COBs. By 2019-2020, quantum board fixtures (HLG, Mars Hydro, Spider Farmer) using hundreds of small Samsung LM301B/H chips spread across flat boards offered: better PPFD uniformity (no hotspots), higher efficiency (2.5-3.0 µmol/J), lower per-watt cost, better passive cooling (heat distributed across larger area), and more even canopy coverage. COB technology persists in budget grow lights and DIY builds but has largely vanished from premium commercial cannabis cultivation. Some specialty applications still use COB — particularly horticultural research where concentrated single-point light sources are needed for spectrum studies.