When evaluating the colour of a painted panel, coated component, plastic part, textile or printed sample, the lighting environment is just as important as the colour itself.
A sample that appears to be a perfect colour match under one light source may look noticeably different under another. This phenomenon can create serious quality-control issues in industries such as automotive painting, industrial coatings, plastics, printing, textiles and product manufacturing.
For this reason, professional colour matching cabinets and visual inspection stations often use multiple light sources rather than relying on a single lamp.
The most commonly used illuminants include D65 daylight, TL84, CWF (Cool White Fluorescent) and UV/BLB. Each has a different purpose and helps users evaluate a product under different lighting conditions.
This article explains the role of each light source and how they can be used in professional colour matching and quality inspection.
Why Is Lighting Important for Colour Matching?
Colour is not simply a fixed property of an object. The colour we see depends on three important factors:
- The light source
- The object being viewed
- The observer
When the illumination changes, the spectral characteristics of the light reaching the object also change. As a result, two samples that appear identical under one light source may appear different under another.
This is one reason professional colour evaluation is often performed under controlled lighting conditions.
Using multiple illuminants can help users identify potential colour differences and metamerism.
What Is Metamerism?
Metamerism occurs when two samples appear to match under one lighting condition but appear different under another.
For example, two automotive paint panels may appear identical under daylight but show a visible difference under fluorescent lighting. This can create problems when a vehicle component is painted, repaired or manufactured under one lighting condition and later viewed by the customer in another environment.
A multi-light colour matching system helps identify such differences before the product reaches the market.
D65 – The Primary Daylight Illuminant
D65 is one of the most widely recognised daylight conditions used for visual colour evaluation.
It represents a standard daylight condition and is commonly used for evaluating paints, coatings, plastics, printed materials and other coloured products.
For the CoatXpert range, the Philips MASTER TL-D 90 De Luxe 18W/965 is used as a professional daylight lamp for compatible colour matching and inspection applications.
Key Characteristics
- Nominal colour temperature: 6500K
- High colour rendering
- Professional fluorescent lamp
- 2-feet T8 format
- Suitable for colour matching and visual inspection
Best Applications
D65 lighting is particularly useful for:
- Paint colour matching
- Automotive refinishing
- Coating inspection
- Colour comparison
- Quality-control workstations
- Colour matching cabinets
- Plastic and industrial component inspection
Why Is D65 Important?
For most professional colour evaluation applications, D65 should be considered the primary viewing condition.
If you are setting up a dedicated colour inspection workstation or replacing lamps in a compatible colour matching cabinet, D65 is generally the most important light source in the system.
TL84 – Fluorescent Commercial Lighting Condition
TL84 is commonly used as an additional fluorescent lighting condition for colour assessment.
It is particularly useful for evaluating how a colour may appear under commercial, retail or fluorescent lighting environments.
In the CoatXpert range, this role can be supported by the Philips MASTER TL-D 18W/840, a professional 4000K fluorescent lamp commonly used in TL84-related colour matching applications.
Key Characteristics
- Nominal colour temperature: 4000K
- Cool White fluorescent illumination
- CRI: approximately 82
- 18W lamp
- 2-feet T8 format
Best Applications
TL84 lighting can be used for:
- Colour matching cabinets
- Retail and commercial lighting simulation
- Automotive paint evaluation
- Industrial colour inspection
- Metamerism evaluation
- Comparing colour appearance under different illumination conditions
Why Use TL84?
A paint sample may look correct under D65 daylight but different under fluorescent commercial lighting.
Checking the sample under both D65 and TL84 conditions can help identify whether the colour remains visually acceptable under different environments.
CWF – Cool White Fluorescent Lighting
CWF stands for Cool White Fluorescent.
This illuminant provides another fluorescent viewing condition and is traditionally used in colour matching systems to evaluate how colours appear under Cool White fluorescent lighting.
For the CoatXpert range, the Philips MASTER TL-D 18W/33-640 provides a Cool White fluorescent lighting condition with a nominal colour temperature of approximately 4100K.
Key Characteristics
- Nominal colour temperature: approximately 4100K
- Cool White fluorescent illumination
- 18W power rating
- 2-feet T8 format
- G13 bi-pin cap
- Suitable for compatible multi-light inspection systems
Best Applications
CWF can be used for:
- Colour matching cabinets
- Colour comparison
- Paint and coating inspection
- Industrial quality control
- Multi-light visual evaluation
- Metamerism checking
Important Difference Between TL84 and CWF
At first glance, TL84 and CWF may appear similar because both are fluorescent light sources with a colour temperature around 4000K.
However, colour temperature alone does not completely define how a light source renders colours. Their spectral characteristics can differ, meaning a sample may respond differently under TL84 and CWF lighting.
For this reason, a professional multi-light colour assessment system may include both light sources.
UV / BLB – Ultraviolet Light for Fluorescence Inspection
UV or BLB stands for Blacklight Blue.
Unlike D65, TL84 and CWF, UV/BLB lighting is not primarily used to visually evaluate the normal appearance of colour. Instead, it is used to detect fluorescent effects and optical brighteners.
The CoatXpert range includes the Sankyo Denki F18T8BLB, a professional UV-A Blacklight Blue fluorescent lamp with a peak wavelength of approximately 352 nm.
Key Characteristics
- UV-A radiation
- Peak wavelength: approximately 352 nm
- 18W fluorescent lamp
- Professional BLB filter glass
- 2-feet T8 format
- G13 bi-pin cap
Best Applications
UV/BLB lighting can be used for:
- Detecting optical brighteners
- Fluorescent material inspection
- Coating inspection
- Fluorescent dye detection
- Specialised quality-control applications
- UV-responsive material examination
Why Is UV Included in Colour Matching Equipment?
Some materials contain optical brightening agents or fluorescent components.
These materials can behave differently when exposed to ultraviolet radiation. Including a UV source in a professional inspection environment can help users identify fluorescent effects that may not be obvious under ordinary visible light.
D65 vs TL84 vs CWF vs UV – Comparison
| Light Source | Typical Characteristic | Primary Purpose | Best Application |
|---|---|---|---|
| D65 | 6500K daylight, high colour rendering | Primary colour evaluation | Paint, coatings, plastics and quality inspection |
| TL84 | Approximately 4000K fluorescent lighting | Commercial/fluorescent viewing condition | Colour matching and metamerism evaluation |
| CWF | Approximately 4100K Cool White fluorescent lighting | Secondary fluorescent viewing condition | Multi-light colour evaluation |
| UV / BLB | UV-A, approximately 352 nm | Fluorescence detection | Optical brighteners and UV-responsive materials |
Which Light Source Should You Use?
The answer depends on your application.
If you need basic colour evaluation:
Start with D65 daylight.
If you operate a colour matching cabinet:
Check which illuminants your existing cabinet requires. It may use a combination of:
- D65
- TL84
- CWF
- UV / BLB
If you need to evaluate colours under different lighting conditions:
Use D65 together with TL84 and/or CWF.
If you need to detect fluorescence or optical brighteners:
Use UV / BLB lighting.
A Recommended Professional Colour Inspection Setup
For a professional colour matching environment, a multi-light approach can provide a more complete evaluation.
A practical inspection sequence may be:
Step 1: Inspect Under D65
Evaluate the sample under daylight conditions and compare the overall colour, hue, lightness and appearance.
Step 2: Switch to TL84
Check how the sample appears under a different fluorescent lighting condition.
Step 3: Check Under CWF
Evaluate the sample under a Cool White fluorescent environment.
Step 4: Use UV/BLB Where Required
Check for fluorescence, optical brighteners or UV-responsive material characteristics.
This approach can help identify potential visual differences that may not be visible under a single light source.
Building a Complete Colour Matching Lamp System
CoatXpert offers professional lamps suitable for compatible colour matching and inspection equipment.
The range includes:
D65 Daylight Lamp
For primary daylight colour evaluation.
TL84 Fluorescent Lamp
For evaluating colour appearance under a commercial or fluorescent lighting condition.
CWF Cool White Lamp
For evaluating colour under a Cool White fluorescent lighting condition.
UV / BLB Lamp
For fluorescence and optical brightener inspection.
Together, these products allow users to source multiple replacement illuminants for compatible colour matching cabinets and dedicated visual inspection workstations.
Conclusion
There is no single light source that can show how a colour will appear in every possible environment.
D65 provides the primary daylight viewing condition. TL84 and CWF provide additional fluorescent viewing conditions that can help reveal changes in colour appearance and metamerism. UV/BLB provides a specialised source for detecting fluorescence and optical brighteners.
For basic colour matching and quality inspection, D65 is often the most important starting point. For more comprehensive professional evaluation, multiple illuminants can provide a better understanding of how a colour or material behaves under different lighting conditions.
By using controlled lighting and the appropriate combination of illuminants, paint shops, coating laboratories, manufacturers and quality-control teams can make more informed visual colour decisions.
Frequently Asked Questions
Is D65 better than TL84?
D65 and TL84 serve different purposes. D65 is generally used as the primary daylight viewing condition, while TL84 provides an additional fluorescent lighting condition for evaluating how colours appear under different illumination.
Do I need both D65 and CWF?
If you require colour evaluation under multiple lighting conditions, using more than one illuminant can be beneficial. However, the correct combination should depend on your application, customer requirements and the design of your colour matching equipment.
Can I use a normal LED light for colour matching?
Ordinary LED lighting may not provide the controlled spectral characteristics required for professional colour evaluation. For critical colour matching, use an appropriate controlled lighting system and follow the requirements of the relevant application or standard.
Why do two colours match under one light but not another?
This is commonly known as metamerism. Two samples can have different spectral reflectance characteristics while appearing similar under one light source. When the illumination changes, the difference may become visible.
What is the difference between CWF and TL84?
Both are fluorescent viewing conditions, but they can have different spectral characteristics. Even when their colour temperatures are relatively close, colours may appear differently under the two illuminants.
Is UV/BLB used for normal colour matching?
UV/BLB is primarily used for detecting fluorescence and optical brighteners rather than normal visible colour evaluation.
