# Optics: Question on rainbow

1. Oct 18, 2014

### Catch22meifucan

In the morning I wake up and there is a amazing light effect that is caused by the sunlight and the chandelier in my living room. However when I use a flashlight to try to duplicate this process I am left with a pathetic duplication. The colors and size in my duplication are non vibrant and small.

What is the difference in the light of a flashlight and sunlight? How might I go about repeating this process?

2. Oct 19, 2014

### Drakkith

Staff Emeritus
There are two things I can think of.

1. The Sun is much brighter than a flashlight, so the colors will be brighter and more vibrant.
2. The light from the Sun may diverge less than light from a flashlight.

3. Oct 19, 2014

### DaveC426913

3. You will only get out what goes in.

The light from the sun is quite broad across the spectrum of visible light, whereas tungsten's is less so.

Your rainbows will be comprised only of bands of light that are in the source.

Last edited: Oct 19, 2014
4. Oct 19, 2014

### Catch22meifucan

Is there a light that I can construct into making it more vibrant and brighter?
And what can i do to make it diverge less?
And what are the best angles to make it the brightest?
How do different chandeliers affect the outcome?

5. Oct 19, 2014

### DaveC426913

Tricky. You can get full spectrum lights, but you'll have a tough time getting them bright like the sun.

I am not convinced this is a thing. I'd like to hear a little more about what Drakkith is thinking.

Well, these are things that will be part of your findings from your experiments! :)

6. Oct 19, 2014

### Drakkith

Staff Emeritus
I'm not convinced either.

Here's something you can try, Catch22. Take a piece of thick paper or cardboard and cut a thin, rectangular slit in it and then shine the flashlight through the slit at the chandelier. This may reduce the overlap between the colors and produce a more vibrant rainbow, but I'm not certain as I don't have a chandelier to test it out on.

7. Oct 20, 2014

### sophiecentaur

I suspect he is thinking along these lines: If the incident light is not well collimated there will be 'bleeding' of light of one wavelength into another. This will / could detract from the purity (saturation / Impact) of the colours in the projected spectrum. Light from more than one angle can arrive at the same location on the projector screen. We are pretty sensitive to chrominance differences, particularly in some areas of the CIE chart. I seem to remember that our colour discrimination is in the order of 2% (probably better than this, bearing in mind we need 8 bits to avoid noticeable contours on near-uniform colour fields.

A Halogen lamp would be better than a normal filament and a Photoflood lamp (over-run filament) could be better still.

You can get very reasonably priced hand held spectrometers and what they show you can be very revealing about some of the light sources we use these days. (LEDs and CFL). Look on eBay and ask for one as a stocking filler this Christmas!

8. Oct 20, 2014

### Drakkith

Staff Emeritus
Yes, that's pretty much what I was thinking. Thanks for explaining!

Yes, I picked up a simple handheld one for a few dollars on Ebay a few years ago. Very interesting.

9. Oct 20, 2014

### Khashishi

Most new flashlights are cheap LEDs, which don't have very broad spectra.