Hard and soft light are different types of lighting that are commonly used in photography and filmmaking. Soft light refers to light that tends to "wrap" around objects, casting diffuse shadows with soft edges. Soft light is when a light source is large relative to the subject; hard light is when the light source is small relative to the subject.
The hardness or softness of light depends mostly on the following two factors:
The softness of a light source can also be determined by the angle between the illuminated object and the 'length' of the light source (the longest dimension that is perpendicular to the object being lit). The larger this angle is, the softer the light source.
Hard light sources cast shadows whose appearance of the shadow depends on the lighting instrument. For example, fresnel lights can be focused such that their shadows can be "cut" with crisp shadows. That is, the shadows produced will have 'harder' edges with less transition between illumination and shadow. The focused light will produce harder-edged shadows. Focusing a fresnel makes the rays of emitted light more parallel. The parallelism of these rays determines the quality of the shadows. For shadows with no transitional edge/gradient, a point light source is required. Hard light casts strong, well defined shadows.
When hitting a textured surface at an angle, hard light will accentuate the textures and details in an object.