Backlights are useful for capturing a silhouette of an opaque object or for capturing the transmission of light through an object. Silhouette imaging is useful for gaging, presence or absence or pinhole detection. Transmission imaging is useful for detecting foreign object contaminants or any defect that might cause a localized change in light transmission. 

MetaPhase Technologies manufactures a wide selection of backlights. The internal LEDs can be located either beneath the surface for direct illumination, or they can be located along the edges for edge-lit arrays. Edge lighting is particularly useful for imaging of biological samples that might be adversely affected by heat, as power is dissipated along the edges of the array rather than directly under the sample.