frontillumination

Frontillumination, often written as front-illumination, is a term used to describe lighting or sensor configurations in which illumination or detection occurs from the front side. In photography and cinematography, front illumination refers to lighting a subject from the same general direction as the camera, producing relatively even lighting with reduced long shadows and a flatter appearance. This setup is common in product photography and portrait work when the goal is to minimize texture and emphasize color and form.

In the context of imaging sensors, front-illumination describes sensors whose photodiodes and circuitry are on the front surface that faces the incoming light. This arrangement can introduce shading and a lower fill factor because metal interconnects and other structures lie between the light and the photosensitive area. Front-illuminated sensors are typically cheaper to manufacture and have been widely used in consumer cameras, but they generally have lower quantum efficiency than back-illuminated sensors, where light enters from the opposite side after thinning or removing obstructions.

Back-illumination is often preferred in scientific and high-end imaging applications due to higher sensitivity, particularly at shorter wavelengths, though some modern front-illuminated designs incorporate microlenses or other techniques to recover performance. In microscopy and other optical systems, front illumination can also refer to illumination from the same side as detection, which may simplify alignment but increase stray reflections if not managed.

See also: back-illumination, image sensor, photography lighting, lighting design.