Professionals engaged in automotive glass, display cover plates, AR/AF coating, architectural coating, and decorative coating daily deal with various optical parameters: Lab*, Y, xy, YI, haze, light transmittance, reflectance, and color difference ΔE.

However, when delving deeper: what exactly does each metric represent? Which performance aspects does it affect? Why is it necessary to test? Even many seasoned professionals can only provide a general concept, unable to explain it thoroughly and clearly.

This article covers everything for you in one go—thoroughly, in detail, and clearly. After reading it, whether you're communicating with clients, quality inspections, or interacting with equipment manufacturers, your professionalism will be instantly elevated.

1. Lab* Color Space (Industry Core, Widely Used)

It is the core reference standard for determining whether the product color is uniform.

L*: The higher the lightness value, the brighter and whiter; the lower the value, the darker and blacker.

a*: Red — Green axis, where positive values lean toward red and negative values lean toward green.

b*: Yellow — Blue axis, positive values lean towards yellow, negative values lean towards blue.

▲ Quick Note: L for light/dark, a for red/green, b for yellow/blue. Whether the color of coated products is consistent depends on the Lab values.

2. The Y value represents the luminosity component in the CIE 1931 standard tristimulus values, indicating the brightness or darkness of a color

Common understanding: it refers to the visual brightness perceived by the human eye.

The higher the Y value → the brighter the visual perception, the stronger the reflection effect

The lower the Y value → the darker the appearance and the weaker the reflective effect

3. x, y values CIE 1931 chromaticity coordinates x, representing the horizontal position of the color on the chromaticity diagram

It belongs to an internationally recognized color precision positioning system, where each fixed set of (x,y) coordinates corresponds to a unique standard color.

x represents the strength of the red component

y represents the strength of the green component

As long as the values of x and y fluctuate, the overall tone will change.

▲: High-end vehicle-mounted AR films, anti-reflective films, and optical glass all use the xy coordinate system to calibrate standard color values.

4. YI Yellowness Index (a mandatory core measurement index for car cover plates)

YI stands for Yellowness Index, representing the level of yellowing.

The higher the value, the more obvious the yellowing

The lower the value, the whiter and clearer the background color, and the stronger the transparency

Why is mandatory testing required in the automotive industry? Because glass coating is prone to yellowing after long-term exposure to high temperature, high humidity, and ultraviolet radiation. The smaller the change in YI value, the better the stability of the film layer and the higher the product grade.

5. Haze (transparency, cleanliness reference)

Haze is used to characterize the degree of fogging, obscuring, and insufficient transparency on the surface of glass.

Low haze: Clear and transparent image, clean appearance

High haze: The surface appears white and hazy, as if covered with a thin mist

AG anti glare glass, car instruments, center console cover, and HUD front cover are all categories that require haze measurement.

6. Transmittance Tt

Total Transmittance， The proportion of light passing through the glass substrate.

The higher the transmittance, the better the transparency and the clearer the vision

The lower the transmittance, the darker the appearance and the stronger the light blocking ability

The core function of AR anti reflective film is to improve light transmittance and ensure that the screen can be clearly visible even under strong light.

7. Reflectance R

Reflectance， Represents the total amount of reflected light on the surface of glass.

High reflectivity → Strong reflection, dazzling vision, and unclear screen visibility

Low reflectivity → Low reflectivity, no glare, clear image, comfortable viewing experience

The core process goal of AR anti reflection film is to reduce the surface reflectivity to the lowest limit!

8. Color difference Δ E (color stability judgment basis)

Δ E is used to measure the degree of color difference between two samples.

Δ E ＜ 1: The human eye is basically unable to distinguish color difference

Δ E ＜ 2: Meets the industry's general qualification standards

Δ E>3: The color difference is clearly visible to the naked eye, and it is directly judged as unqualified

The stability of color in mass production depends on the level of Δ E control! 

9. Gloss (distinguishing between glossy and matte textures)

Used to measure the brightness of the product surface.

High glossiness: High gloss and glossy texture, with a metallic luster

Low glossiness: Matte low-key texture, more advanced and introverted

10. Refractive index n (core basic parameter for process engineers)

The underlying key parameters of the coating industry.

Directly decide:

Design thickness of membrane layer

The advantages and disadvantages of AR anti reflection effect

Is the color tone of the product offset

Once the refractive index parameter is inaccurate, all subsequent coating processes lose their significance.

11. Penetrating color difference Δ T (color difference in transparent state)

Check whether the color remains consistent when observing external objects through glass. Mainly applicable to: display glass, instrument panel cover, AR anti reflective film and other products.

Final summary

Lab * determines color, Y value determines brightness and darkness, xy calibrates standard color, YI measures yellowing degree, haze measures transparency and cleanliness, transmittance measures incoming light intensity, reflectivity measures reflection strength, and Δ E controls batch color consistency.