Light sources is a broad general term encompassing any natural or artificial source of illumination used in photography to light a subject, scene, or environment for the purpose of making an exposure. The choice of light source - its type, quality, colour temperature, intensity, direction, and the way it is modified and controlled - is one of the most fundamental creative and technical decisions in photography, as the character of the light falling on a subject is the single most influential factor in determining the mood, atmosphere, tonal quality, and overall visual impact of the final image.
Natural light sources used in photography include sunlight in all its many manifestations - the warm, directional light of sunrise and sunset, the harsh overhead light of midday sun, the soft and even illumination of an overcast sky, the cool blue light of open shade, and the subtle gradations of light on cloudy or partly cloudy days. Each of these natural lighting conditions has its own distinctive colour temperature, quality, and directional character that creates a different visual effect on the subject, and understanding and working with natural light is a fundamental skill for outdoor, landscape, portrait, and reportage photographers.
Artificial light sources used in photography span an enormous range of types and technologies, each with its own specific characteristics in terms of colour temperature, spectral output, intensity, and practical suitability for different photographic applications. Tungsten and tungsten halogen lamps produce a continuous warm toned light at around 3200 Kelvin and were for many decades the standard artificial light source in photographic and film studios, valued for their consistency and the ability to see and adjust the quality and direction of the light before shooting. Fluorescent lamps produce a cooler, more diffuse continuous illumination, while HMI and plasma discharge lamps offer daylight balanced continuous output at high intensities suited to large studio and location lighting setups.
Electronic flash - both portable on camera flash units and studio flash systems - is the most widely used artificial light source in professional still photography, producing an extremely brief and intense burst of daylight balanced light that freezes motion, complements or overpowers ambient daylight, and can be precisely controlled and modified with a vast range of accessories. LED lighting panels and arrays have emerged as an increasingly important category of continuous artificial light source in both still photography and video production, offering energy efficient, daylight balanced, variable colour temperature illumination in compact and portable form factors that make them practical for a wide range of studio and location applications.
The colour temperature of a light source - measured in Kelvin - determines the overall colour cast it imparts to the image, and matching the camera's white balance setting to the colour temperature of the prevailing light source is essential to achieving accurate and neutral colour reproduction. Different light sources within the same scene can produce mixed colour casts that present challenges for white balance correction, and understanding the colour characteristics of different light sources is an important aspect of colour management in photographic practice.