The present subject matter relates to methods of high-speed analysis of product samples. Light is directed to a portion of a product under analysis and reflected from or transmitted through the product toward a plurality of optical detectors. Signals from the detectors are compared with a reference signal based on a portion of the illuminating light passing through a reference element to determine characteristics of the product under analysis. The products under analysis may be stationary, moved by an inspection point by conveyor or other means, or may be contained within a container, the container including a window portion through which the product illuminating light may pass.