SMD (Surface Mount Device) LEDs
SMD LEDs are individual LED components mounted on a PCB (printed circuit board). Each SMD chip is a small discrete unit - typically 2835, 3030, 5630, or similar numerical designations referring to the chip dimensions in tenths of mm. Multiple SMD chips are arranged in a matrix on the PCB inside the fixture. Advantages: individual chips can be replaced if one fails. Good thermal distribution across the PCB. Wide variety of beam patterns achievable with lens placement over individual chips. Used in: most commercial LED street lights and flood lights. Quality indicator: check the chip brand (Cree, Osram, Seoul Semiconductor, Bridgelux, Nichia = premium tier; generic Chinese = variable quality).
COB (Chip On Board) LEDs
COB packages multiple LED dies directly onto a substrate without individual packaging - creating a single high-density light-emitting area. The result: very high lumen density from a small area, uniform circular light source appearance, simpler optics (one lens covers the whole COB), and very high power density possible (50W+ from a single module). Used in: high-power flood lights, spotlights, high-bay single-source designs. Disadvantages: if one die in the COB fails, the entire module must be replaced. Higher thermal density requires excellent heat management. COB is not inherently better or worse than SMD - the application determines which is appropriate.
How to Judge LED Chip Quality
Bin grade: LED manufacturers produce chips in bins - sorted by actual output (lumens), colour temperature, and voltage. Premium manufacturers use tightly binned chips (e.g., SDCM 3-step MacAdam ellipse for colour consistency between fixtures). Cheap products use wide-bin chips - lights in the same project look noticeably different colours. Ask for the chip brand and bin specification. Phosphor quality: the phosphor coating over the die determines colour quality (CRI) and its degradation determines lumen maintenance over time. Premium phosphor (Cree, Nichia) degrades slowly. Cheap phosphor yellows within 3–5 years. Operating current: premium chips are driven at 60–75% of their rated current - generous derating extends life dramatically. Cheap products over-drive chips at 100–120% for high initial lumens - fast degradation follows.
