The Science of Standard-defined Colour: Why Hi-Vis Fluorescent Orange and Yellow Have Colourimetric Limits

Key Takeaways

• Hi-vis fluorescent colours are defined by CIE 1931 chromaticity coordinates, not by how bright a colour looks to the eye.
• AS/NZS 1906.4:2023 sets out seven designated colour spaces: green, yellow-green/lime yellow, yellow, orange, orange-red, red, and pink. Green and pink were added in the 2023 revision.
• Brightness and colour are tested as two separate properties: chromaticity (the “where on the chart” measurement) and luminance factor (the brightness measurement).
• Testing happens under a standardised light source, CIE Standard Illuminant D65, with garments measured dry. Wet-weather materials must still retain most of that brightness when wet.
• A garment can fade, wash out, or sun-damage its way outside the compliant coordinate range while still looking “bright enough” to the naked eye.
• Independent testing labs check garments against these coordinates using spectrophotometers, not visual judgement.
• Some specific figures in this article, including exact coordinate values and the current minimum luminance factor, are flagged for confirmation and are not published pending verification against the current standard.

AS/NZS 1906.4 fluorescent colour is not simply about choosing a bright shade of orange or yellow. Hi-vis colours are defined by specific colourimetric limits, measured with laboratory instruments against a fixed colour space. A garment either falls within the required coordinate range or it does not.

In this article, we explain how fluorescent colours are scientifically measured, what the colour coordinates and limits mean, and why they matter for hi-vis compliance. We also look at how colour performance can affect garment visibility and consistency.

At Reflective Fabrications (RF), we apply this understanding throughout our manufacturing process to help ensure hi-vis products meet the relevant requirements.

What “Fluorescent” Actually Means

Fluorescent hi-vis fabric does something an ordinary bright colour cannot. It absorbs invisible ultraviolet light from daylight and re-emits some of that energy as visible light, on top of the light it normally reflects. That extra emitted light is why a fluorescent orange vest looks like it is glowing on an overcast day when a painted orange sign next to it looks flat and dull by comparison.

This is also why fluorescent hi-vis works so well in daylight and does almost nothing at night. Artificial lighting contains very little UV, so the fluorescent boost disappears once the sun goes down. That is the entire reason hi-vis garments split into daytime fluorescent materials and night-time retroreflective tape, rather than relying on one material to do both jobs.

The Colour Space: How Chromaticity Coordinates Define Compliant Orange and Yellow

Every colour the human eye can see has a numerical address. Colour scientists use x and y coordinates to plot colours on the CIE 1931 chromaticity diagram.

For hi-vis materials, these coordinates define where a compliant colour must sit on the chart:

• Inside the boundary: The colour meets the specified chromaticity range.
• Outside the boundary: The colour does not meet the specified range.
• Near the boundary: Small changes caused by fading, washing or UV exposure can potentially affect compliance.

How AS/NZS 1906.4 Defines Hi-Vis Colours

AS/NZS 1906.4:2023 uses the CIE 1931 chromaticity system to define its designated fluorescent colour spaces. These include:

• Green
• Yellow-green (lime yellow)
• Yellow
• Orange
• Orange-red
• Red
• Pink

Each colour space is a defined area rather than a single colour or shade. This means two garments from different manufacturers can look slightly different while both remaining compliant, provided their measured colour coordinates fall within the relevant boundary.

Why Colour Names Alone Are Not Enough

This is an important distinction that is often missed when discussing hi-vis colours. Saying that orange, yellow or red are approved hi-vis colours does not tell you whether a particular fabric is compliant.

The colour must meet the measured chromaticity limits specified by the standard. A spectrophotometer measures the material and determines where its colour falls within the CIE 1931 colour space.

In other words, hi-vis colour compliance is based on where the colour is measured, not simply on how it looks to the eye.

Luminance Factor: The Second, Separate Test

Colour and brightness are not the same measurement, and AS/NZS 1906.4:2023 tests them separately. Chromaticity tells a lab where a colour sits on the chart. The luminance factor, often written as Y, tells the lab how bright that colour is, on a scale where black sits near zero and white sits near one.

A fabric can have exactly the right hue and still fail if it is too dull. This is why some faded garments look like they are “still orange” to a casual glance but would not pass a lab test. The eye is reasonably good at judging hue and poor at judging small changes in brightness, especially outdoors where lighting conditions vary constantly. That is precisely why the standard does not rely on a visual check.

How Compliance Is Actually Measured

Hi-vis colour compliance is not determined by visual inspection. Testing laboratories use calibrated instruments and controlled conditions to determine whether a material meets the requirements of AS/NZS 1906.4:2023.

Colour and Brightness Are Measured Separately

For fluorescent materials, chromaticity and luminance are assessed under Clause 2.3 of the standard. Non-fluorescent materials are assessed separately under Clause 2.4.

The measurements are compared against the colour and luminance requirements in Appendix A.

• Chromaticity: Determines where the colour sits within the specified colour space.
• Luminance factor: Determines how much light the material reflects and therefore how bright it appears under the test conditions.

A Spectrophotometer Measures the Material

Rather than relying on visual judgement, laboratories use a spectrophotometer to measure the material’s colour properties.

Testing is carried out using CIE Standard Illuminant D65, a standardised light source designed to represent average daylight. This provides a consistent reference for testing, regardless of where or when the material is tested.

Materials Are Tested Under Defined Conditions

Garments and materials are measured dry as the baseline condition. Materials designed for wet-weather use are also tested when wet.

Under Clause 2.6, wet-weather materials must retain a specified proportion of their dry-state luminance. The exact requirement should be confirmed against the current edition of AS/NZS 1906.4:2023 before specifying a numerical value.

Why Standardised Lighting Matters

“Tested in daylight” might sound straightforward, but natural daylight changes constantly depending on the time of day, season, location and weather conditions.

Using a standardised illuminant removes these variables. A garment tested in a Melbourne laboratory in winter and one tested elsewhere in Australia can therefore be assessed against the same controlled light source and measurement conditions.

This makes colour compliance measurable, repeatable and independent of subjective visual judgement.

Why a Garment Can Look Fine and Still Fail

A hi-vis garment does not remain compliant simply because it was compliant when it was new. Colour performance can change over time, and those changes may not be obvious to the naked eye.

What Can Affect Fluorescent Colour?

AS/NZS 1906.4:2023 includes colourfastness testing for several conditions that can affect a material’s colour performance, including:

• UV exposure from sunlight
• Washing and laundering
• Acidic perspiration
• Alkaline perspiration

The standard also includes testing of chromaticity and luminance after extended washing, using a standardised washing procedure. This helps assess whether a material continues to meet the required colour and brightness limits after repeated laundering.

How Colour Changes Over Time

Fluorescent dyes can gradually degrade through repeated exposure to sunlight and washing. This can cause the material’s measured colour coordinates to shift and potentially move outside the specified colour boundary.

Perspiration can also affect colour performance. Testing under both acidic and alkaline conditions helps assess how the material responds to the types of sweat it may encounter during regular wear.

Why Visual Inspection Is Not Enough

The biggest issue is that these changes happen gradually. A garment may become slightly less vibrant with every wash or period of UV exposure, but the difference may be too subtle for someone wearing it every day to notice.

A vest can therefore look bright enough while its measured colour performance has changed.

That is why colour compliance relies on laboratory testing rather than visual judgement. For workplaces issuing hi-vis clothing, regular inspection, appropriate laundering and timely replacement are important parts of maintaining visibility and safety.

How AS/NZS Compares Internationally

Australia is not the only country to use defined colour limits for hi-vis fluorescent materials. Other jurisdictions have their own standards, colour spaces and testing requirements.

Different Standards, Different Colour Boundaries

For comparison:

• Australia and New Zealand: AS/NZS 1906.4

[New Zealand also applies specifications such as NZTA E06:2023 for high-visibility safety garments.]

• United States: ANSI Z535.1
• Europe and the UK: BS EN ISO 20471

These standards define their own chromaticity boundaries for fluorescent colours, including orange and yellow. As a result, the same material can fall within the compliant colour range of one standard but outside another.

Why the Difference Matters

A peer-reviewed study examining fluorescent orange safety garments used in the Australian railway industry found that the AS/NZS fluorescent orange colour space is wider and shifted towards yellow compared with the equivalent ANSI and BS EN ISO colour spaces.

The study also found that some garments that failed the Australian and US colour requirements after UV exposure continued to pass the ISO requirements. This highlights an important point: international hi-vis colour standards are not simply different names for the same colour limits.

There Is No Single “Compliant Orange”

For organisations sourcing hi-vis clothing internationally, this distinction matters.

“Compliant orange” is not one universal colour. Compliance depends on the specific standard applied and whether the material’s measured chromaticity falls within its defined boundaries.

A material that passes AS/NZS 1906.4 should not automatically be assumed to meet ANSI Z535.1 or BS EN ISO 20471 requirements without separate verification.

What This Means for Buyers and Safety Officers

The practical takeaway is straightforward. A visual check, “Does this still look bright?”, is not a compliance check. Colour compliance under AS/NZS 1906.4:2023 is a measured property that degrades with UV exposure, washing, and time, and the only way to know for certain whether a garment is still inside its compliant colour space is to test it, or to replace gear on a schedule that assumes degradation is happening even when it is not obvious.

For procurement and safety teams, this points to two practical habits: sourcing hi-vis materials from suppliers who can demonstrate current test certification against AS/NZS 1906.4, rather than relying on a garment’s original compliance claim indefinitely, and building garment replacement into a maintenance schedule rather than waiting for a visible fade to trigger it.