Rainbows are pretty amazing things. Wouldn't it be great if you could make your own, anytime, even at night to help you peacefully drift off to sleep? I think so! Follow along if you'd like to make your own rainbow night-light!

First off, if you're interested in how a rainbow is formed and why white light separates when it passes through a prism check out one or both of these videos below.

It's okay to be smart

Physics girl

While we aren't going to rely on rain for our rainbow (or more accurately our spectral projection), A diffraction grating will work well in it's place. A diffraction grating is a set of many small prisms packed into a small space. These, similar to water droplets, can split white light into all the colours in our visual spectrum. An example of a diffraction grating you can find around your house is a DVD or CD. So we'll be using one of these to help make our rainbow. I found DVDs seem to give a better image, so I'll be using one in this Instructable.

Supplies

The great thing with this project is that you probably have everything you need laying around your house. And it can be completed in 15 to 30 minutes!

Here's what you'll need to follow along with the build.

1. A bright white flash light (I'm using an LED night-light/flashlight from a company called Sunbeam, you can use a cellphone flashlight/torch or other bright white light)

2. A tissue box

3. A DVD

4. Some card-stock (I'm using a cereal box)

5. A pair of tweezers

6. A pair of scissors and/or a utility knife

7. Four paperclips

8. Isopropyl alcohol or some soapy water and paper-towel

9. A stack of books or CD cases about 5cm tall.

10. A ruler

11. A protractor

12. A marker

13. Some tape

14. A wooden skewer (longer than your box is wide) OR eight neodymium magnets (I'm using rectangular ones 2x5x10mm)

Step 1: Prep the Housing

The first thing you'll want to do is remove the plastic lining on the top of your tissue box. This will give us a cleaner looking rainbow. Then make the opening wider by cutting to the top edges of the box.

Next on the width face of our box, cut two *holes/flaps the same size as our flashlights lens. One hole/flap should be centred at the top, and the other centred at the bottom.

* You can see in the pictures I cut holes, but if I were to do it again, I'd make flaps, so I could keep one closed while using the other

Step 2: Prep DVD

The DVD can be used as is, but by separating the 2 layers, we'll get a more vivid rainbow.

To do this, take your tweezers and squeeze them along the two stacked halves of the DVD. Doing so will create a small separation between the two pieces. Now carefully pull the shiny side away from the clear side.

We'll be using the shiny side. If there is purple adhesive left on the shiny part, you can clean it with the Isopropal Alcohol or soapy water and paper towel. Don't over do the cleaning or you could start to take off the reflective surface like I did.... Despite this, I can still get good rainbows.

Step 3: DVD Angle Adjustment

Option A: Magnetic adjustments (pictures 1-3 of this steps images)

I prefer this setup because it's easy to make quick adjustments.

Along the outer perimeter of the DVD, take two magnets and stick them together with the disc between them, making DVD-magnet sandwich (picture 1). Do the same with two more magnets across the DVD, 180 degrees from the first two magnets (picture 2)

Put the DVD into the tissue box and lay it flat on the bottom, shiny side up. Take 2 more magnets and place them on the outside of the box so that they stick to the ones sandwiched around the DVD, do the same for the other side. You should now be able to adjust the DVD and have it stay in place.(picture 3)

Option B: Wooden skewer adjustments (pictures 4-8 of this steps images)

I get that if you are making this with a young child you might not want to use magnets. This setup isn't as flexible to modify things on the fly, but it still works well. We'll make a flap that the DVD will rest on, and secure its angle with the wooden skewer.

With a utility knife, cut along both bottom length edge of your box from 4cm to 15cm (from your light source side). then cut straight across the bottom of the box at 15cm(picture 4). You should now have a tab that your DVD can rest on.You can tape your DVD in place (shiny side up) to make sure it doesn't slide down (picture 5).

Next, use a protractor to measure a 25 degree incline for your DVD flap (you can choose a different angle, but I wouldn't go beyond 40 degrees) (picture 6). Do this on both sides of your box then poke two holes at these points and thread the skewer through the opening behind the flap that the DVD is resting on (pictures 7&8).

Step 4: Limiting Light

We now need to make two sliding sheets to block out any stray white light that would overpower our rainbow.

To do this, cut out two pieces of cardstock (cereal box), each large enough to cover the tissue box top opening. Bend one piece to about 60 degrees 5cm from the edge (for a cleaner look, you can score it using a utility knife and a ruler).

Step 5: Making Rainbows!

Great, now you're ready to start making some rainbows!!

Light position

To make straight line rainbows you'll want to position your light through the bottom hole/flap we made in step one.

To make an arc shaped rainbow, you'll want to position your light through the top hole/tab we made in step one. To do this, you'll need to stack something underneath the flashlight.

Adjusting card-stock sliders

To best adjust the card-stock sliders, first slide one along the top of the box lengthwise until you start to see a rainbow. Keep sliding until you see colour start to fade from the rainbow. Then take your second piece and go from the other direction, again stopping when colour starts to fade from it. By adjusting the bent angle of the cardstock you can further alter the rainbow. You'll know when you're in a good position when you can't see any bright white light on the wall or ceiling. Once they are in a good spot, you can hold them in place with your paper clips.

Wall or Ceiling

If you're using your cellphone, turn the box 90 degrees and rest your cellphone on top of it where the light can travel through the holes you made. This will put the rainbow on the wall as opposed to the ceiling.

Step 6: Going Further

(i) Even more rainbows!

You can create even more effects, by moving your flashlight around freehand over top the tissue box. I've included some images I took when I was doing this... See what other shapes you can make!

(ii) Getting in focus.

Take a magnifying glass and hold it between the wall and your rainbow, move the magnifying glass until you can see which part of the DVD your rainbow is coming from!

(iii) Editing the rainbow

If we put a piece of transparent coloured plastic over the light source or over the tissue box opening,We can limit the amount of colours in our rainbow. You can also do this with a bit of food colouring and water in a clear glass. Try a few colours and guess which colours will or won't be shown in the projected rainbow. This is pretty much how a spectrometer works! By looking at a rainbow spectrum through a material and seeing how it affects the that spectrum, we can find out what exactly we're looking at.