The Effect of a Diffuser in Front of the LED

A diffuser can help spread out the light more evenly across the projected beam of light emitted by the LED. To demonstrate this I place the diffuser of an old slide viewer next to the LED.

I then placed the frosted glass plate in front of the slide viewer diffuser and took a picture to show its angular distribution.

A spotmeter indicated that the center of the distribution was EV = 8.1 which corresponds to a luminance of 38.2 cd/sq meter.

So the diffuser spreads out light more evenly and can compensate to some extent for the flaws of the light source. It may also widen the viewing angle of the LED.