backillumination

Backillumination, also referred to as back-illumination, is the practice of illuminating a subject or detector from the side opposite the observer or camera. The term is used across photography, imaging technology, and display engineering to describe arrangements that place light sources or illumination behind the object being observed or imaged, or to describe sensor architectures that expose the photosensitive area to light from the rear.

In photography and cinematography, back illumination or backlighting means lighting the subject from behind. This creates rim lighting and separation from the background, often yielding a glow around edges and silhouettes. It is frequently combined with fill light to control mood, depth, and texture, and is a common technique for emphasizing shape or creating a sense of atmosphere.

In imaging sensors, back-illumination refers to back-illuminated sensor designs in which the photodiode layer is positioned at the back of the silicon substrate. This removes front-side metal routing from blocking light, increasing quantum efficiency and improving low-light performance and color accuracy. Back-illuminated CMOS sensors require specialized manufacturing but have become widespread in digital cameras and smartphones.

In display technology, back-illumination denotes lighting from behind the display stack. Backlit LCDs use a diffuse light source beneath the liquid crystal layer to create a bright, uniform image. Direct or full-array backlighting contrasts with edge-lit configurations and is a key factor in brightness, contrast, and power efficiency.

See also: backlighting, backlit display, back-illuminated sensor, rim lighting.