No need to look so far. The logo for Half-Life was always the Greek letter lambda (certainly because it's often used in physics and chemistry to represent the decay constant, which is a simple function of half-life). And that level is probably just named in keeping with the game's identity.

I still remember when my chemistry teacher first drew a lambda on the chalkboard and said "this will give us the half-life". I felt like all the pieces finally came together in my life.

Yes, I know that defeats the point of using lambda, but I felt the joke was worth it.