A packaging technique resulting in a packaged array of LED chips that all share the same substrate. The phosphor covers the entire array of LED chips so the light-emitting area is not a point but a wide light source. The advantage is that the space is smaller, since each LED chip doesn’t require its own ceramic substrate, phosphor and lens. In addition, assembly costs can be lower, and electrical connection to the LED array can be from the top through a solderless plastic connector. The disadvantage is that heat sinking is crucial, and, because the light emitting area is so large, it’s difficult to focus the light; COB packages often don’t have any lensing. If you look closely at the CXA3070 pictured below, the faint lines you can see outline the positions of the LED die under the phosphor.
CRI (Color Rendering Index)
CRI measures of the quality of light: The light source’s ability to render color. The higher the CRI, the better the light source renders colors in the visible spectrum. CRI values can range from 0 —the worst— to 100 —(ideally) the best. To have what is generally considered good color rendering, a source must be 90 CRI or better. R values — sometimes called the Special Color Rendering Index (Ri), R values are a subset of the overall CRI score for a light, and measure the light’s ability to render the individual colors. The two most important R values are R9 (red), especially important in measuring skin tones and food, and R12 (blue).