Iridescence is caused by interference patterns in different colors of reflected light. You'll have to experiment. Find out the light source direction when the iridescence is maximum. A circular polarizer may enhance or totally kill the iridescence so that's another experiment. If I remember correctly the iridescence of snake scales is caused by a thin film effect. In butterflies, it's caused by the scales acting as a diffraction grating.

Being a big boy, so to speak, I will say that I stand corrected and offer you an apology. I also did some research and do indeed find that, although apparently very much more rarely, we do get rainbows in the west with rain in the west at shortly after sunrise, but, something that does not occur here where I am butted up against the Rockies. I guess I've just been here in Colorado too long. We rarely ever get rain in the morning here in our semi-arid climate and when we do, the sun isn't usually shining. Even if those conditions are present, I think the mountains would interfere with the development of a rainbow.

Due to heat buildup over the Divide in the mornings, clouds release and move out over the flat lands in early afternoon which is when we get our rains with the sun in the west completing the conditions that are necessary for rainbow formation. Our worst moisture ladden weather comes to us from the east, including the majority of the snow we get along the front range of the mountains. A low pressure cell sits up down about Albuqurque forming a counter clockwise flow that brings us moisture from the east and then the afternoon buildup I described above often follows that so our moisture is mostly always in the east. I suppose I allowed that to condition my thinking.

As for the polarizer, I watched the youtube and read the comments below but am not convinced at this point. It does not, in my mind, make much sense. Next time I get a chance which is pretty often, I will put that to a test and start a thread with the results.

Well, that's all quite simple really, if I may....but first, as a slightly interesting sidebar, while I'm not partial to a lot of bragging myself, now that you mention it, I've got a sign on my wall right above my monitor that an old friend gave me because of my overabiding modesty that says, "Him who can bragg without lying, let him bragg." He seemed to think I needed 'punching up' some.

Back to the changes to which you allude, I think here in the U. S. we have probably changed the language more than perhaps you folks in N.Z. and Aus have from what I think I know and from what you say. We 'hospitalize' people while back in Britain they 'put them in hospital.' We saved a few valuable letters on that, no doubt, just as an example of how we have whittled away at it and made it better. Perhaps it would help you to understand a little better if you were to realize that you apparently have failed to get the word that the United States is the greatest country of all time in the whole wide world and we know how to make everything better than everyone else so it's only fitting that we change the several thousand year old language that has only withstood the test of time and make it better, don't you think. Why, even our esteemed President, several of them in fact, on several occasions, have been noted as saying so on the worldwide stage, beamed by sattelite so the whole rest of the world can be insulted simultaneously in 'real time.' We even have people sitting on the sidewalks playing a guitar and rattling tin cups begging for change who say that as well. It must be true.

Thanks Pulseight. I used the term blue light because the term LED didn't come to me at the time of writing. I have a variety of LED lights and some of them are LED torches, others you can hang or stick on the wall.

:-)