The three rules of light for photography are the direction, quality, and quantity of light. The direction of light is the most important factor in creating a well-lit photo. The quality of light is determined by its intensity and color. The quantity of light is determined by the amount of time the shutter is open.
Light travels in straight lines
The speed of light is always the same, no matter how fast you are moving. It takes about 8 minutes for light from the sun to reach Earth.
Light can be reflected, refracted, or absorbed. When light hits a surface, some of it may bounce off the surface (this is called reflection). If the surface is smooth, like a mirror, the reflection will be very bright. If the surface is not smooth, like paper, the reflection will be less bright. Some surfaces can cause light to bend (this is called refraction). This happens when light goes through glass or water. The ray of light bends because it slows down as it goes through these materials. Finally, some surfaces can absorb light so that you can not see any reflections at all (this happens with dark colors).
The subject receives less light as the distance to the light source is increased
The amount of light that is available to illuminate a subject decreases as the distance from the light source increases. This is due to the inverse square law, which states that the intensity of light at a given point decreases in proportion to the square of the distance from its source.
In photography, this means that subjects will appear darker as they get further away from your light source. This can be used to create mood and contrast in your images, or simply to ensure that your subject is properly lit.
To avoid this problem, you can either move your light source closer to your subject or use a more powerful light.
The larger the light source relative to the subject, the softer the light source
Light plays a critical role in photography, and there are three key rules that every photographer should understand in order to make full use of its potential. First, larger light sources relative to the subject will result in softer lighting. This is due to two factors: first, because there is more area over which light can spread out, and second, because light sources that are close to subjects tend to produce harsher shadows. Second, brightness falls off according to what is known as the inverse square law. This means that if you double your distance from a point source of light, its brightness will decrease by a factor of four. And if you triple your distance, its brightness will fall off by a factor of nine, and so on. Finally, surfaces reflect more light when they are perpendicular (at right angles)to the direction of incoming light than when they are at other angles. This relationship is described by what is known as the cosine fourth law and results in what we perceive as shininess or specular highlights on surfaces like metal or glass.