Bright Field vs Dark Field Lighting – and why it matters
Friday 21 Nov 2025 · 3:15
This can seem complicated at first, but once you grasp the concept of Bright Field vs. Dark Field Lighting, you’ll see why it’s so useful in a machine vision system application.
Being able to apply the correct type of lighting to your machine vision system could completely transform the results you’re getting.
We’ve seen many situations where improvements to the lighting alone can increase reliability and decrease downtime of your production line.
So, if you’re having reliability issues with your machine vision system, read on to learn about the difference between bright field and dark field lighting and how it can be used to feed the correct information to your system.
What’s the difference?
When a vision system camera is pointing down at an object, the boundaries of the field of view (what that camera can see) look like an inverted 'V':
The vision system camera can’t see anything outside of these boundaries. Of course, the exact field of view will vary depending on which camera/lens you’re using. But the principle is the same, regardless.
Because 'angle of incidence = angle of reflection', the
field of view boundary lines reflect back up at exactly the same angle.
This gives us a virtual 'W':
Bright Field Lighting
Now, if we imagine shining a light on our subject from within the
W, that light will be reflected back up to the camera. Lighting the object from
within the W is called Bright Field Lighting.
We’d use bright field lighting when we need to see the light
reflected back up to the camera – usually when we want to light the object so
the camera can see all of it, for example.
It may sound strange to hear that you wouldn’t want to see
all of the object, but this will become clear when we look at the use cases for
dark field lighting.
Dark Field Lighting
Alternatively, if we imagine shining a light from outside
the W, and that light is hitting a flat surface beneath the camera, the camera
won't see that light reflected:
Lighting the subject from outside of the W is called Dark
Field Lighting – sometimes referred to as Low Angle Lighting.
At first, dark field lighting sounds useless right? But it
has a very important function when it comes to machine vision systems.
Although we won’t see dark field light reflected off a flat
surface, we will see it reflected off features that aren’t flat.
For example, there could be a scratch, chamfer or radius on
the part being inspected. When the dark field (or low angle) lighting hits one
of these features, the angle of the surface on the feature will cause the light
to reflect up to the camera.
With the vision system camera being able to see that
feature, it can report back to the system for the next action that needs to be
taken. This could be to measure the feature or reject it from the production
line.
The video below was called "one of the simplest explanations on bright field vs dark field that I've heard so far" by one industry expert.
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