With object of an easy explanation, I propose the window experiment consistent of three mode of passing light through a window, which helps us to study on what the light consists.
As we see in the drawing, we use a window that allows the pass of light in three different positions, which are: 1.- Open window, 2.- single (double, etc.) slit, and 3.- camera obscura experiment.

1.- Opened window,

Here we see that light, colors, bright, dark and penumbra are mixed among them giving finally simple luminosity inside of the room and in front of the wall to the window.
Say, here all type of light is mixed forming an only one form of light.
Then here we could think that light are particles, that light are waves, or that light have double composition as particles and waves.

2.- Single (or double) slits,

When being very small the slits, here we see as light only is projected on the frontal wall of the room.
Here the light and colors form stripes or fringes with the mixture of color belonging alone to the light that pass in straight line from the exterior to the wall or screen in the bottom of the room.
Then here we start to think that light move in straight line, and so, we begin to believe that light are particles but not waves.

3.- Camera obscura vision,

Here we already understand that light are only particles and not waves, because of what we see in the bottom of the screen are the perfect figure of the exterior landscape figure in inverted way.
But why this occurs, because of when particles of light go in straight line each one of them, they can form a perfect figure, impossible of getting if they were waves.
In this case, if light were waves, these waves must to be mixed in the point C of penetration forming the same diffused luminosity than in the case 1.

Here, device of camera osbcura for using in multiple modes of experiment by mean of a window with different cards to make experiments like: The open window, single, double or more slits experiment, camera obscura experiment, etc.