Yeah, especially with these cheapo Chinese LEDs. I looked into spectrometers, but they seem pretty pricey. Maybe some sort of plastic filter that blocks the shorter wavelengths?

How about a simple prism? That would tell you instantly if there's any blue light in the stream.

Edit: You might need a mask to create a slit of light so you can see the spectrum clearly.

Oh, yeah! Totally forgot about those from high school chemistry class. :)

I'm sure there'll be _some_ blue light. I don't know if a prism would be high resolution enough to tell if it's a dangerous level.

Yeah, you won't be able to see the intensity, but you will be able to see what components of the spectrum are there. It's also and easy way to test filters.