A video spectral comparator (VSC) is a desktop instrument that combines several controlled light sources, a set of optical filters, magnification and a camera in one enclosed housing. It lets a document examiner view a document under precisely chosen wavelengths of light, from ultraviolet through visible to infrared, and capture and compare the results on screen.
It is the standard second-line and laboratory instrument for questioned documents. Whether you need one depends on the questions you are asked to answer, not on the volume of documents you see.
What a video spectral comparator does
The value of a VSC lies in control. A handheld UV torch gives you one wavelength, at whatever angle you hold it, in whatever ambient light the room has. A VSC fixes all of those variables.
Controlled illumination. The instrument offers a range of light sources in one place: white light from above, from a low angle and from behind, ultraviolet at more than one wavelength, and infrared. Because the document sits inside an enclosure, ambient light is excluded.
Filters on the camera side. Light sources determine what goes onto the document. Filters in front of the camera determine what comes back to the sensor. Combining the two is what allows an examiner to separate one ink from another, or to see infrared luminescence, where an ink excited by visible light emits in the infrared.
Magnification and image capture. A camera with optical and digital zoom records what the examiner sees, at a known magnification, with the illumination settings stored alongside the image.
Comparison. Images can be viewed side by side or overlaid, so a questioned document can be compared against a reference, or one area of a page against another under identical conditions.
Which examinations need spectral control
Several questions in document examination can only be answered reliably when the wavelength of the light and the filter on the camera are both known.
Ink differentiation. Two inks that look identical in visible light can behave differently in the infrared. One absorbs and stays dark, the other becomes transparent. That is the basis for detecting added digits, altered dates and overwritten entries. Our article on wat infrarood laat zien dat UV niet kan explains the principle.
Infrared luminescence. Some inks emit infrared light when they are excited by visible light. Seeing that emission requires strong visible illumination and a filter that blocks everything except the infrared. It is difficult to achieve without an enclosed instrument.
Obliterated and erased entries. Text covered by ink or correction fluid can sometimes be read when the covering material transmits in the infrared and the original ink does not.
Security feature verification at second line. Features designed to respond at specific wavelengths, including UV features at more than one wavelength and anti-Stokes inks that respond to infrared excitation, can be checked against a reference under repeatable conditions.
Documented comparison. When a finding has to be reported, an image taken with known settings carries more weight than a description of what was seen under a handheld light.
What handheld UV, IR and magnification already cover
Most document checks never need a VSC. At the first line, the questions are whether expected security features are present and whether anything looks altered. Handheld tools answer those questions well.
- A UV flashlight at 365nm shows UV-reactive features, fluorescent fibres and paper that fluoresces when it should not.
- A 10x to 15x magnifier with oblique light resolves microprint, print processes, laser engraving and relief.
- A portable infrared camera at 850nm shows which inks absorb in the infrared, enough to spot many substitutions.
- A handheld magnifier with several light sources combines magnification with UV, oblique, transmitted and sometimes anti-Stokes light in one unit.
The combination of these tools, used in a fixed order, is described in IR, UV en vergroting combineren in één onderzoek. It covers the majority of first-line findings.
Workflow: handheld first line, VSC second line
The most common arrangement is a tiered one.
First line. Officers at the counter or the border check the document with handheld equipment and a short routine. Their task is to pass, refer or retain, not to reach a forensic conclusion.
Second line. A referred document goes to a specialist with more time and better equipment. This is where a VSC or a desktop examination system earns its place: the specialist can work through the light sources systematically, compare against reference material and record the result.
Laboratory. Cases that require handwriting comparison, ink analysis or a formal expert report go to a forensic laboratory, which will use a VSC alongside other instruments.
Between handheld tools and a full VSC sits a middle tier of desktop systems. These combine multiple light sources with optical and digital magnification and a screen. The Forensic Examinator, for example, offers top, oblique, side and transmitted white light, UV at 365nm and 254nm, IR at 850nm and 940nm, 980nm anti-Stokes laser light, 3x and 5x optical magnification and 8x to 100x digital magnification on a 7 inch display. For many second-line posts, a system of this kind covers the checks they actually perform.
Questions to ask before you invest
A VSC is a significant purchase, and it needs trained users to deliver value. Before choosing one, answer these questions honestly. The full examination sequence is described in our guide to forensic document examination.
- What questions are we asked? If the work is mostly “is this feature present”, handheld tools and a desktop system may be enough. If it includes ink differentiation, obliterations and reportable findings, spectral control becomes necessary.
- Who will operate it? A VSC in the hands of an untrained user produces images, not findings. Factor in training and time to build experience.
- Which wavelengths and filters do we need? Match the light sources and filters to the documents and features you examine, rather than buying the widest range by default.
- How will results be recorded? Check how images, settings and notes are stored, and whether that fits your reporting and evidence procedures.
- What reference material is available? A VSC compares. Without reliable reference material for the documents you see, comparison is limited. See referentiemateriaal opbouwen.
- Where will it stand? Spectral work benefits from a controlled room. Our article on verlichting van de werkplek covers the basics.
Veelgestelde vragen
Is a video spectral comparator the same as a document scanner?
No. A scanner captures an image under fixed illumination. A VSC lets the examiner choose the illumination and the filter, and view the document live at different magnifications.
Do border control officers need a VSC?
First-line officers generally do not. A VSC is a second-line and laboratory instrument. First-line staff are better served by handheld magnifiers, UV lights and a clear referral route.
What is the difference between a VSC and a desktop document examination system?
Both combine several light sources with magnification and a screen. A VSC typically offers finer control over wavelengths and filters and more extensive image comparison. Desktop systems cover the core checks at a smaller scale.
Can an infrared camera replace a VSC?
For spotting many ink substitutions, a portable IR camera is very effective. It does not provide the filter control, the range of excitation wavelengths or the documented comparison that a VSC offers.
Equipment from first line to second line
Dexeq supplies handheld and desktop equipment for document examination, from UV flashlights and multi-light magnifiers to forensische onderzoekssystemen en IR-camera's. If you are deciding what a second-line post needs, een offerte aanvragen and describe the checks you carry out.
Written by the Dexeq editorial team. Dexeq was founded in 2011 by a former officer of the Royal Netherlands Marechaussee with 18 years of service, 11 of them as a document fraud expert.
