If you want to see if the individual dies of your Led are operating normally without burning your retinas, simply shine your light into a body of water and look at the reflection of the LED in the water. A cup, bucket, or bathtub of water will work fine for this or even the toilet. (I strongly suggest flushing it first!)
:toilet:
I first read about this method on CPF and I've done it with a Cree MC-E LED. I was skeptical at first but it actually worked fine.