Lighting Geometry Selection Guide
Application Requirement Object Under Inspection Suggested Type of Illumination
Reduction of Specularity Shiny Object Diffuse Front, Diffuse Axial, Polarizing
Even Illumination of Object Any Type of Object Diffuse Front, Diffuse Axial, Ring Light
Highlight Surface Defects or Topology Nearly Flat (2-D) Object Single Directional, Structured Light
Highlight Texture of Object With Shadows Any Type of Object Directional, Structured Light
Reduce Shadows Object With Protrusions, 3-D Object Diffuse Front, Diffuse Axial, Ring Light
Highlight Defects Within Object Transparent Object Darkfield
Silhouetting Object Any Type of Object Backlighting
3-D Shape Profiling of Object Object With Protrusions, 3-D Object Structured Light
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testing & detection targets illumination cameras imaging lenses microscopy lasers optomechanics optics
TECHNICAL NOTE
Telecentric Illumination.................................... 399
LED Illumination....................................... 399-407
Backlights......................................... 402-403, 413
Ring Lights........................................ 405-406, 411
Structured Illumination............................. 408-409
Fiber Optic Illumination............................ 410-411
Fiber Optic Light Guides.......................... 410-417
Fiber Optics..................................................... 417
HOW IMPORTANT IS ILLUMINATION?
Customers often struggle with contrast and resolution problems in an imaging
system while underestimating the power of proper illumination. In fact,
desired image quality can often be met by improving a system’s illumination
rather than by investing in higher resolution detectors, imaging lenses
and software.
Correct illumination is critical to an imaging system and improper illumination
can cause a variety of image problems. Blooming or hot spots,
for example, can hide important image information, as can shadowing. In
addition, shadowing can also cause false edge calculations when measuring,
resulting in inaccurate measurements. Poor illumination can also result
in a low signal-to-noise ratio. Non-uniform lighting, in particular, can harm
signal-to-noise ratios and make tasks such as thresholding more difficult.
These are only a few of the reasons why correct illumination for your application
is so important.
To ensure optimal illumination when integrating a system, it is important
to recognize the role that the right components play. Every component affects
the amount of light incident on the sensor and, therefore, the system’s
image quality. The imaging lens’ aperture (f/#) impacts the amount of light
incident on the camera. Illumination should be increased as the lens aperture
is closed (i.e., higher f/#). High power lenses usually require more
illumination, as smaller areas viewed reflect less light back into the lens. The
camera’s minimum sensitivity is also important in determining the minimum
amount of light required in the system. In addition, camera settings such as
gain, shutter speed, etc., affect the sensor’s sensitivity.
TELECENTRIC
ILLUMINATION
• Produces high contrast
silhouette images for increased
edge contrast
• Employs glass optics to
collimate the light from a fiber
optic light guide or spot light
• Ideal for measurement and
gauging applications when used
in conjunction with a telecentric
imaging lens
STRUCTURED
ILLUMINATION
• Utilizes specific patterns of light
to determine the geometric
shape and depth of objects
• An effective 3D system can be
constructed by illuminating
objects with different patterns,
such as grids, dots, or lines
• Types of products include laser
diode modules and pattern
projectors
LED ILLUMINATION
• LEDs are a bright, long life time
illumination option
• A wide range of wavelengths
are available
• Available geometries include
ring lights, backlights, line lights,
diffuse axial lights, spot lights,
and more
FIBER OPTIC
ILLUMINATION
• Fiber Optic Illumination
often consists of an illuminator
integrated with a light guide for
versatility
• Illuminators are available in
LED, Metal Hallide, and Quartz-
Halogen light sources
• Light guides are available in
quartz, liquid, visible and UV
• Available geometries include
ring lights, backlights, diffuse
axial lights, and more
Figure 1: Clear Edge Silhouette
from Telecentric Illuminator System
Figure 2: Blurry Edges from
Standard Backlight System
Inside Illumination
Common Structured Illumination Patterns