The PT17-21B/L41/TR8 is a blue SMD LED from Everlight in 0603 (1608 metric) package with a dominant wavelength of 470nm. The LED uses InGaN (Indium Gallium Nitride) epitaxy on a sapphire substrate. When forward-biased above the typical 2.8V threshold, electrons in the n-type layer recombine with holes in the p-type layer, emitting photons at the InGaN bandgap energy corresponding to blue light (470nm). The /L41 designation specifies the luminous intensity bin (typically 50-120mcd at 20mA). The /TR8 suffix indicates tape-and-reel packaging with 8mm tape width, suitable for automated SMT assembly. Maximum forward current is 30mA continuous, 100mA peak (0.1ms pulse, 10% duty). The 0603 footprint (1.6×0.8mm) is suitable for high-density PCB designs. Viewing angle is typically 120 degrees for diffused-lens variants. Typical applications include status indicators, backlighting, and RGB LED arrays where the blue channel provides the shortest wavelength component.