The cathode is denoted by the flat on the body & the short lead. The LEDs have either a water-clear lens with a narrow viewing angle of 30deg or a diffused lens with a wide viewing angle of 60deg Specifications Order Code UK51F Clear Red Kingbright description L-53SRC-CViewing angle 30deg Forward current max.30m A Forward voltage max.2.5 V Reverse voltage max.5 V Wavelength peak 660nm Power dissipation PT100m W Light output min. 20m A800mcd Light output typ. 20m A1000mcd Order Code UK20W Clear Red Kingbright description L-53SRC-EViewing angle 30deg Forward current max.30m A Forward voltage max.2.5 V Reverse voltage max.5 V Wavelength peak 660nm Power dissipation PT100m W Light output min. 20m A2000mcd Light output typ. 20m A2800mcd Order Code N45AT Clear Red Kingbright description L-53SRC-FViewing angle 30deg Forward current max.30m A Forward voltage max.2.5 V Reverse voltage max.5 V Wavelength peak 660nm Power dissipation PT100m W Light output min. 20m A3500mcd Light output typ. 20m A4000mcd Order Code UK19V Diffused Red Kingbright description L-53SRD-EViewing angle 60deg Forward current max.30m A Forward voltage max.2.5 V Reverse voltage max.5 V Wavelength peak 660nm Power dissipation PT100m W Light output min. 20m A300mcd Light output typ. 20m A400mcd