Quality Magazine

Lighting Strategy

June 9, 2010

Lighting is simply one part of a vision and sensing system, but it is a critical part. Its function is to make the integrated system simpler, faster, and more reliable. System dependence on extensive computer data processing can not only make the system much slower, but can reduce reliability.

Decision Making Module & Lighting

Vision and sensing systems consist of image/signal acquisition, a decision making module and a control module.

The decision making module is critical, and the image/signal acquisition should be focused on simplifying this function. The image and signal acquisition should provide the best contrast, discrimination, Signal-to-Background (or Signal-to-Noise) ratio.

My mental image for the ideal defect image to be sensed by the camera or photosensors is a bright spot on a dark background: like a train with a headlight coming out of a dark tunnel on a black night. Then simple, fast threshold operations can be used with minimal computer processing.

The ideal image for an edge to be used as a position marker for gauging should have a bright area, with high contrast, against a dark background. It should have high contrast or at least a reproducible slope of intensity.

Lighting and Signal Processing

The best lighting provides the best images.

The best images provide the best signals.

The best signals provide the simplest, fastest and most reliable signal processing.

The stand-alone word “lighting” sets up the wrong mental image. Lighting is not just shining light, as lighting a room. (Even room lighting has different applications such as lighting for offices, living rooms, bedrooms.)

I prefer “targeted lighting”, where the optics exploits the optical properties of the target (for example, object of interest) . In a very real sense, the target is the critical optical component in the optical system.

Targeted Lighting

The “targeted lighting” should be designed to exploit the optical properties of this critical optical component.

In my experience, when confronted with an on-line sensing problem that had resisted reliable solutions by internal and/or external groups, the features that initially gave me a knot in the stomach usually turned out to be optical characteristics that could be exploited for simple solutions. Simple solutions are often only simple in hindsight.