This is so easy and obvious, it's probably not even worth mentioning.

I'm fiddling around with my Arduino and TLC5940, and I'm getting a headache from staring at them. But, I don't want to sand them down, or otherwise permanently diffuse them, and putting them behind a sheet of paper or typical diffuser won't let me clearly see the specific patterns I'm trying to achieve.

Amazingly, straws fit atop generic 5mm LEDs ''perfectly''.

What you need:

    * Straws (Normal, cheap ones. Bendy-style optional)
    * Scissors
    * LEDs you want to diffuse.

Figure out a decent length, then cut. Mine are about an inch and a half, as the crow flies.

After cutting, stick your straws onto the LEDs. They should rest nicely on top.

If you're anal-retentive like me, tape them together, so they stand up together.

My inspiration came from Mitch Altman's Trippy RGB Waves. I thought it was a brilliant idea, and as such, I'm passing it on to you :)

I've also posted this as an Instructable.