OneBoxVision Blog

Learn why LED lighting is preferred for 100% inspection systems

LED lighting has emerged over the last number of years as the norm for 100% inspection. This article highlights how LED lighting compares older lighting techniques. 

LED lighting is now the norm for 100% inspection!

Over the past 15 years all inspection companies have used different light solutions for its 100% inspection systems. This document explains the different light solutions and their benefits. Let's look at the following technologies.
  • Xenon strobes
  • Fluorescent tubes
  • Tungsten Halogen
  • LED solid state illumination

Xenon Strobes

  • Can only be used with area scan cameras and thus used often in vision systems for print inspection, but are not suitable for 100% inspection.
  • The light intensity output of a strobe is not stable at all. Variations in intensity between two consecutive strobes from up to 10% are no exception, especially when the bulb starts getting older.
  • Typically, the bulbs must be replaced every 3-6 months (15Million strobes) and are they are expensive.
  • Strobes cannot be used with to light any highly reflective substrate (foils, metallised films, reflective paper…)
  • Light output degrades over life time of the bulb
  • Light output varies with temperature variation of the bulb
  • Color varies with temperature variation of the bulb

  Fluorescent

  • Used commonly by suppliers on systems up to 2010.
  • Introduces low intensity levels of high frequency AC flicker on inspected image. 
  • Noise due to AC power supply (low or high frequency)
  • There is no possibility to control intensity levels.  The intensity of fluorescent tubes cannot be reliably controlled as the gas inside the fluorescent tube is very unstable.
  • Light intensity output is not consistent over time and with change in ambient temperature.
  • Light intensity is very low compared to Focused LED or Tungsten Halogen light. 
  • Fluorescent tubes must be replaced every six months.
  • Only diffuse light can be generated.

 Tungsten Halogen (Fibre Optic)

  • Bulbs have a very short life span. Lasts between 500 and 700 hour depending on bulb type and how hard they are driven.
  • Non uniform light output.
  • Bulbs are expensive, ranging from 25.00Euro to 40.00Euro each.
  • Color of light output is approximately 3,500K.
  • Very high level of red and green color content.
  • Very high maintenance. It is necessary to keep spare light control boxes and lots of spare bulbs in stock. 

LED Light

  • Very long life span. Designed to last up to 100,000 hours (7 to 10 years)
  • Reliable due to use of solid state technology and often temperature controlled
  • Low maintenance so no bulb replacement.
  • Light output is very stable (No Flicker)
  • DC-powered
  • LED solid state technology
  • Resulting in clean noise free inspection images thus better defect detection
  • Light output is very even along its length.
  • Very high intensity
  • Lenses bundle and focus the light
  • Results in smaller apertures, sharper images and thus better inspection
  • Color temperature of light output is 6,700K which is equal to the color recommended for use with the line-scan cameras.

The table below summarizes the results. 



 

Strobe

Fluorescent

Halogen

LED

Suitable for 100% inspection

No

Yes

Yes

Yes

Suitable for repeat to repeat inspection

N/A

Yes

Yes

Yes

Suitable for 100% benchmarking GTC

N/A

No

Yes

Yes

Suitable for full color inspection

Medium

Medium

Poor in blue vector 3200K

Medium

5600K

Yes

Programmable color temperature

No

No

No

Yes

Maintenance

Bulb change

1

Bulb change

2

Bulb Change

1

None

3

Light source

Bulb Gas discharge

1

Bulb Gas discharge

1

Tungsten wire

2

Diode

3

Life time

15M flashes / 3-6 Months

6 Months

2

<3 Months

1

100’000H

3

Light intensity

Uncontrollable

1

Low

1

Medium

2

High

3

Cost

Cheap

Cheap

Expensive

Expensive

Spectral stability

Bad

1

Medium

2

Medium

2

Very Good

3

Substrates

Non reflecting

1

Almost all

2

All

3

All

3

Diffuse light

N/A

Yes

Yes

Yes

Focused light

N/A

No

Yes

Yes

Noise

Yes

 High frequency
 AC-noise

1

Little

3

Little

3

Intensity

Fix

1

Fix

1

Variable, but color temp changes 1

Variable, without spectral change 3

Uniformity 

N/A

0

Poor

1

Poor

1

Very Good

3

 

 Summary

LED illumination should be the default of all modern inspection solutions, unless an application has a particular requirement for a characteristic found in one of the other technologies. In the past 5 years, OneBoxVision has become the leader in web and sheet inspection.

Download Whitepaper >

Topics: Vision system solutions Print inspection systems Surface inspection systems 100% Inspection