SPECTROMETER VS COLORIMETER
Wavelengths vs Colour — a spectrometer measures the light spectrum in detail, while a colorimeter measures colour characteristics, usually expressed as colour coordinates or related values. For AGL work, a spectrometer provides more detailed spectral information, while a colorimeter is generally a faster instrument for direct colour measurement and verification.
At a Glance
| Feature | Spectrometer | Colorimeter |
|---|---|---|
| Main purpose | Measures the spectral distribution of light | Measures the colour of light |
| Main question | What wavelengths are present, and how much? | What colour is the light? |
| Output | Spectrum: intensity vs wavelength | Colour coordinates/colour values |
| Spectral detail | High | Limited/no detailed spectrum |
| Colour measurement | Can be derived from spectral data | Primary function |
| Speed | Often slower/more analytical | Often faster |
| Complexity | Generally higher | Generally simpler |
| AGL use | Detailed optical and colour analysis | Routine colour verification |
Spectrometer & Colorimeter
Spectrometer
A spectrometer separates light into its different wavelengths and measures their distribution across the visible spectrum. It answers: "What is the spectral composition of this light?"
Colorimeter
A colorimeter is primarily designed to measure and quantify the perceived colour characteristics of light or a surface. It answers: "What colour does this light correspond to in a defined colour-measurement system?"
Wavelengths vs Colour
Easy memory: Spectrometer → breaks light into wavelengths. Colorimeter → gives a colour measurement.
Green Taxiway Centreline Light
Consider a green taxiway centreline light measured by both instruments.
Spectrometer Result
Provides detailed information on the distribution of emitted energy across wavelengths — showing why the light has the colour it does.
Colorimeter Result
Provides a direct colour result, such as a "green" reading expressed as colour coordinates — quantifying the colour result directly.
The spectrometer shows why the light has its colour; the colorimeter quantifies the colour result directly.
What Each Instrument Reveals
| Spectrometer | Colorimeter |
|---|---|
| Measures individual wavelength components | Measures overall colour response |
| Produces a spectral distribution | Produces colour values |
| Can reveal multiple spectral peaks | Usually does not show spectral peaks |
| More diagnostic information | Faster colour information |
Two different LED designs can produce a visually similar colour while having different underlying spectral distributions. Depending on the measurement and observer conditions, the resulting colour values may be similar even though the spectral compositions differ.
Can One Instrument Do the Other's Job?
Spectrometer → Colour?
Yes. Colour characteristics can generally be calculated from appropriate spectral measurement data — spectral data → wavelength distribution → colour calculation → chromaticity values.
Colorimeter → Spectrum?
No. A colorimeter does not provide the same detailed wavelength-by-wavelength spectral information as a spectrometer — it is designed for colour-related measurements, not a complete spectral analysis.
Correct Colour, Different Spectrum
Two AGL fixtures may both produce an acceptable apparent green colour, yet their internal light-generation technologies may produce different spectral distributions. A spectrometer can reveal those differences, while a colorimeter focuses primarily on whether the resulting colour characteristics meet the relevant measurement criteria.
When to Use Each
Spectrometer
- Detailed spectral analysis
- Wavelength-by-wavelength data
- Investigation of LED spectral characteristics
- Detailed optical diagnostics
- Calculation of multiple spectral/colour quantities
Colorimeter
- Routine colour checks
- Rapid colour measurement
- Colour-coordinate verification
- Comparison against specified colour limits
The appropriate choice depends on the required test method and applicable AGL specification.
Accuracy Isn't Automatic
More detailed spectral information does not automatically mean every spectrometer is more suitable for every colour measurement. Measurement suitability depends on required accuracy, calibration, spectral range, resolution, measurement geometry, detector characteristics, and the applicable test method. The instrument and procedure should be appropriate to the specific parameter being verified.
How This Connects to Photometry & Colorimetry
Full Engineering Parameters
| Parameter | Spectrometer | Colorimeter |
|---|---|---|
| Measures spectrum | Yes | Generally no |
| Measures wavelength distribution | Yes | No detailed distribution |
| Measures colour | Can derive it | Yes |
| Chromaticity calculation | Possible from spectral data | Direct purpose |
| Spectral peaks | Visible | Not normally available |
| Diagnostic capability | High | Moderate |
| Measurement speed | Often slower | Often faster |
| Instrument complexity | Generally higher | Generally simpler |
| Routine AGL colour checking | Useful | Often practical |
| Detailed LED investigation | Very useful | Limited |
Spectrometer vs Colorimeter
Spectrometer and colorimeter answer different questions. The fundamental difference is what the instrument reports — a full wavelength-by-wavelength spectrum, or a summarized colour result.
A spectrometer gives detailed spectral information that can support calculation of colour quantities and is well suited to diagnostic and investigative work. A colorimeter gives a fast, direct colour reading suited to routine verification against a colour requirement. Which is appropriate depends on whether the objective is detailed optical analysis or verification of resulting colour characteristics.
For AGL: use spectral measurement when detailed analysis of the light source is required; use colour measurement when the objective is to verify the resulting colour characteristics against the applicable requirement.
Engineering & Expert Notes
Choose the Instrument for the Task
SelectionUse what the requirement and test method call for.
Record Calibration and Method
ReportingInclude instrument details.
Compare Results Only Between Compatible Instruments
InterpretationDifferent devices can differ.
Control Measurement Geometry
SetupKeep distance and angle consistent.
Frequently Asked Questions
Spectrometer → wavelengths (a full spectrum). Colorimeter → colour (a summarized colour result).
Yes. Colour characteristics can generally be calculated from appropriate spectral measurement data, since spectral data can be converted into chromaticity values.
No. A colorimeter does not provide the same detailed wavelength-by-wavelength spectral information as a spectrometer — it is designed for colour-related output rather than full spectral analysis.
Different light-generation technologies (e.g. different LED designs) can produce a visually similar colour while having different underlying spectral distributions — something only a spectrometer will reveal.
A colorimeter is generally faster for direct colour measurement and routine verification, while a spectrometer is often slower but more analytical and diagnostic.
Not automatically. Measurement suitability depends on required accuracy, calibration, spectral range, resolution, measurement geometry, detector characteristics, and the applicable test method — not spectral detail alone.
Governing Documents
For an actual project design, always verify the current edition of the applicable documents.
FAA AC 150/5340-30
Design and Installation Details for Airport Visual Aids — colour and photometric requirements relevant to interpreting spectral and colorimetric measurements in AGL specifications.
ICAO Annex 14, Volume I
Aerodrome Design and Operations — colour characteristics of aeronautical ground lights and applicable colour limits.
CIE Colorimetry Standards
International Commission on Illumination definitions and methods for chromaticity calculation from spectral data and direct colorimetric measurement.
Final Engineering Note
Confirm which measurement method the governing standard actually requires — spectral or colorimetric — before selecting an instrument or acceptance criterion.
A spectrometer shows why a light has its colour; a colorimeter simply tells you what that colour is.
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