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Emission Pattern of LED

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The far-field spatial distribution of intensity is typically referred to as the emission pattern ofthe LED. Far-field patterns are typically observed at distances much larger than thewavelength (λ). For the communication grade LEDs, the emission pattern is of significantinterest because the light emitted from the LED is to be coupled into an optical fiber. For efficient coupling, the angular width of the emission pattern should be within the numericalaperture of the fiber. For display LEDs, the emission can be as broad as possible so that light is emitted from all possible angles.The typical emission of LED follows a Lambertian profile, shown in Slide 30. The emitted intensity (I) from a Lambertian source is described as, I = I0cosθ where θ is the angle measured with respect to the normal and I0 represents the maximum value of the intensity.The polar plot of the intensity corresponding to a Lambertian source is shown in the slide below. Commercial LEDs also have a dome structure on top, which can help to alter the emission pattern.