Natural light is the most beautiful and varied of a photographer's light sources. It is inflexible in that it comes from a single source, the sun, but changeable and capable of delivering extraordinary effects. It is undoubtedly true that an eye trained to notice subtle changes sees a visually more interesting world.
The characteristics of sunlight change with atmospheric conditions, the time of day, the angle at which it strikes the earth, and the passage of the seasons. However, daylight has a higher colour temperature than light produced by domestic lamps, and is therefore generally bluer. Indeed, film balanced for tungsten light exhibits a distinct blue colour cast when exposed to daylight.
Early morning light has a frailty and freshness found only at this time of day. It produces a cool, delicate atmosphere with long shadows and deepening hues. The air is moist and often quite still, and wonderful mysterious effects are created as the sun warms the air at first light. On overcast or misty mornings the tendency is towards the cooler blue end of the spectrum. The light is more diffused, the mood more intimate and contrast significantly reduced.
In the middle of a clear day the overhead sun is effectively a harsh white point source. Contrast is marked and hues are at their magnificent brightest. Stark conditions such as these require care, because deep shadows make portraiture difficult. If the sky is cloudy or overcast the light is softened, shadows are less dense and contrast is reduced but colours may also be less intense. These gentler conditions are easier for photographers to handle.
As the sun falls closer to the horizon, and its rays travel further through the atmosphere, a warm romantic glow appears. The longer wavelengths of light at the red end of the spectrum penetrate further, and so will be the last we see before the bluer light of night descends. Shadows lengthen and the low-angle rays emphasize texture. The light is diffused and tinged with gold as it paints the western sky, but changes very rapidly at this time of day. Sunset can be a magical time for photographing people but speed is vital. The best conditions do not last very long.
Seasonal changes in the nature of daylight are also well known in many parts of the world. The European spring brings optimism as nature's fresh colours relieve the grey days of winter. Summer is bright and cheerful with intense light, but colours can be muted by reflection and glare. Autumn is moody, moist and colourful. The light is lower in angle and slightly redder than in summer, but particularly soft at this mellow time of year. Winter is sombre and can be grey and dull as the days shorten. But in cold, cloudless conditions there is a bleak freshness that brings exceptional clarity.