The visible light spectrum
I think this is the actual answer because:
As many have noticed, rainbow seems to fit, but technically a rainbow is only in the sky and due to rain and other water droplets in the atmosphere. So it would technically be the continuous visible light spectrum from red to violet.
Rarely you may think I'm see, often though can I be found
Many people (children would make up a big portion of this) think that refracted light in the form of "ROYGBIV" is only seen in rainbows, but really, you can see it from refraction through many things. Sprinkler, prism, etc.
You can find me in the falls
Can be seen in waterfalls due to refraction of white light by water droplets
Glowing well above the ground
Well, refraction isn't actually due to the water glowing, but it gets the point across.
Bending beauty in the sky
Rainbow is an example of the refraction spectrum of white light, in which case it's an arch in the sky.
Interesting to the eye
Uses all the colors we can see.
Varied lightwaves arching high
See "Bending beauty" above.
ROYGBIV, as noted by Z. Dailey. Also, if you're actually an engineer (as your name suggests), there is a good chance you, like I, would get pedantic about minor discrepancies like this when it comes to physical phenomena.