Light theory can be used in different ways but in photography its used to create different effects for pictures. we can use light to reflect of objects to refract and diffract light.
Refraction
Refraction is the bending of a wave when it enters a medium where its speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the lightray toward the normal so that the boundary between the two media refract. Refraction is responsible for image formation this is one by the lenses and the eye. An example of refraction is that we make object seem likes it bending by using refraction. we were refracting light to make it seem like the object we were using was bending. We used light in many different ways to show this . Light waves change speed when they pass through the boundary between two substances with different densities. This causes them to change direction, this is called refraction. If they cross the boundary at 90 degrees refraction doesn't take place, it carries on straight. When a light hits an object, the light ray hits the object at an angle, its speed and direction then changes. The ray is then bent back into its original direction and it leaves the block. In the picture below we did an experiment to show an object that looks like its bending through light.
Reflection
light waves reflect of surfaces. when waves reflect they obey the law of reflection, angle of incidence equals the angle of reflection. The normal is a line drawn at right angles to the reflector. The angle of incidence is between the incident ray and the normal. The image below show that the mountain is reflection onto the water creating a reflection. This is because light hits the object creating it reflect on the surface. In a ray diagram, the mirror is drawn a straight line with thick hatchings to show which side has the reflective coating. The light rays are drawn as solid straight lines, each with an arrowhead to show the direction of travel.
Spectrum of light
White light can be split up into a spectrum of loads of different colours. Using a light prism, you can split up white lights to form a spectrum. Light waves are refracted as they enter and leave the prism. The shorter the wavelength of the light, the more it is refracted. Red light is refracted the least and violet light is refracted the most making the coloured light to spread out to make a spectrum. Light spectrum means the visible spectrum.The colour of an object that we can see is the colour of light reflected. All of the rest of the colours are absorbed.
The photos above show the experiments we did using a prism. We set up a light box to produce coloured light will hit the prism which is a few cm away from the light box. In between the two there is a slit where you can put different colours lenses to show light. The light reflects onto the table creating a reflection. You can move the slit closer to the prism to improve the colour.
Drawing with Light
To draw with light you need to set your camera to manual mode and then set the aperture to the widest possible. Then set your ISO to the lowest to lowest possible setting and then set it up on a tripod. Then select the shutter speed between 5-30 seconds. Turn one of your light sources on and draw. Move your light source around and draw what you want.