Background suppression, Dark surfaces, Laser Sensors, Object recognition, Reflex scanner, Sensors, ToF sensors, Triangulation sensors, Types of light

Which type of light is the right one for my optical button?

“Blue light, red light, infrared or laser – what do I take and when?”

We regularly get this question from maintenance technicians, designers and special machine builders. And it is absolutely justified, because the type of light is a decisive factor in whether a sensor switches reliably – or not.

The choice always depends on two things: the object and the environment.

Energetic reflex sensors (red light / infrared)

Reflex sensor tests nonwoven material in coffee capsule production — Reflex sensor with red light detects the inserted nonwoven material in the production of coffee capsules.

These sensors work on the principle of the amount of light reflected. The more light comes back from the object, the greater the possible sensing distance.

Typically suitable if:

bright objects are to be detected
The background is light-absorbing (e.g. black conveyor belt)
There are no highly glossy or deep black surfaces

Not suitable for:

very dark objects
reflective surfaces
Strong color differences in the process (different sensing distances!)

Reflex sensor with background suppression (blue light)

Blue light reflex sensor detects small plastic parts on conveyor belt — Blue light technology enables reliable detection of small components with low reflection.

Here, it is not the amount of light that is evaluated, but the angle of reflection (triangulation principle). This means that the sensing distance remains almost colour-independent.

Ideal for:

Black or shiny objects
Changing surfaces
Precise detection at close range
Applications where you want to ignore the background

Blue light has advantages here, as the shorter wavelength penetrates less deeply into challenging surfaces.

Laser distance sensors with time-of-flight measurement (ToF, red/IR laser)

Time-of-Flight Sensor Detects Insulation Mats — ToF laser distance sensor checks the presence of insulation material

When distances become greater or objects are positioned at an angle, classic reflex sensors reach their limits. This is where ToF sensors come into play.

Advantages:

Large ranges
Very high insensitivity to ambient light
Reliable detection even with inclination, gloss or color change
Can be mounted side by side without mutual influence

wenglor in particular also uses wintec technology , which enables measurements independent of colour and surface.

Laser Distance Sensors Triangulation (Red/Blue Laser)

Laser distance sensor measures height of parquet floorboards on conveyor system — Triangulation sensor precisely measures the material height of wooden panels in production.

When it comes to high-precision distance measurements – sometimes in the μm range – there is no way around triangulation.

Typical applications:

Thickness measurement
Position control
Quality Inspections
Surface Measurement

Regardless of color, structure or shape, these sensors provide very stable readings at close range.

Infrared – when visibility interferes or dust flies

Sensor detects traffic jam on scissor roller conveyor in conveyor technology — Optical sensors monitor the material flow on a scissor roller conveyor.

IR light has a wider beam angle and is often used when:

the point of light should not be visible
dusty or foggy environments
larger working areas are needed

Disadvantage: Very small objects are more difficult to detect.

In a nutshell

Situation	Recommended light type
Light object against dark background	Red light / infrared (energetic)
Black, glossy or changing surfaces	Blue light (background suppression)
Long distance, difficult angles, ambient light	Laser Time-of-Flight
Highest measurement accuracy	Laser Triangulation
Dust, fog or invisible light point desired	Infrared

Why this matters

An incorrectly selected sensor type often leads to sporadic false triggers – e.g. after a packaging change or in the case of dirty optics. If you choose the right type of light, you will avoid exactly these problems from the start.