How to Choose the Right AG Glass Gloss Level

What Is AG Glass Gloss and How Is It Measured?

Gloss Magnified Specular Ratio describes the amount of specular reflection at a 60 degree angle compared against a measured black glass calibration standard rated at 100 GU. (gloss units) a higher gloss value indicates a high reflection of light in a mirror type reflectance from the AG glass surface; conversely, a low gloss indicates strong anti-glare diffusivity.

The testing protocol for this system is based on ASTM D523. ASTM D523 specifies three different geometries for the evaluation of glossiness; the 60° geometry is the standard starting geometry applied to any surface prior to additional test geometries. When the 60° reading registers in excess of 70GU, a second reading of the sample is recommended at 20° in order to differentiate the high gloss surfaces more precisely, the decrease in angle offering improved resolution. When the surface has very little light intensity in transmission in relation to the 60° measurement and reads less than 10GU, a third test data point at the 85° geometry allows the measurement of the minimal reflection that the lowest gloss surfaces generate.

In practice, anti-glare glass AG surfaces measured around 100 GU on average. An untreated soda-lime glass panel measures about 110 GU. After etch, the glass surface micro-grooves induce in the AG glass scatter incident light, increasing the dispersion of the reflected light and lowering the gloss values from around 15 to in some cases 95 GU, depending on the depth of etch applied and the size of the gravel particles in the micro-texture. When the gloss value remains around or above 100 GU, then optical clarity exhibits a significant haze of 90+ percent; as the GU value decreases, haze increases, and more anti-glare gloss level becomes available in the image.

The Relationship Between Gloss, Haze, Transmittance, and Clarity

The performance of ag glass is closely related appears to have four distinct parameters that are separately responsive to diametrically different physical effects. gloss appears to capture the specularity of the surface, by catching specular reflection; haze measures the percentage of scattered light of transmitted light which passes more than 2.5° from the source beam; transmittance measures the percentage of the broader transmitted light beam which passes through the glass; and clarity – also called image clarity (DOI) – measures the accuracy with which the glass can reproduce fine high-contrast detail on the transmitted or reflected image.

This system is ruled by one fundamental rule: the higher the gloss, the lower the haze. When the surface roughness prevents diffuse reflection on the AG glass, lower gloss is detected; when the roughness leaves more haze remaining in the transmitted image, the gloss drops accordingly. Transmittance of ag glass is not dramatically affected by etching – even heavily etched AG presents 86+ percent total transmittance. This is because the haze only affects the angular distribution of the passing light, redistributing it. AG glass will still transmit light through its entire thickness, it is just that the scatter angle is now wider.

Clarity: this is one parameter that catches many engineers unprepared. A panel with very low haze and transmittance (and consequently very high DOI) can still look blurry if the surface micro-structure creates micro-lensing effects. There is no penalty in having an unequal distribution of gloss versus the etch pattern: the correlation with clarity is not linear at all – it is a function of the separation (spatial frequency) of the etch structure and the pixel density of the display in place. In general: the higher the clarity requirement, the narrower the window of acceptable gloss.

How Surface Roughness and Etching Create Different Gloss Levels

Every ag glass panel begins with a primitive smooth sheet (either soda-lime or aluminosilicate glass), polished up with sheer glass finesse. Anti-glare performance starts in the etching bath – an aqueous hydrofluoric acid (HF) etch attack – are initiated at a very carefully balanced rate. Etch depth may range from 0.05 mm/hr to 0.07 mm/hr – in that very thin film there is varied formation of microscopic peaks and valley structures from which the light reflected is scattered.

Surface roughness refers to the geometrically defined characteristics of those bumps and hollows – Ra (raw) or arithmetic roughness. After the etching – the size of the micro particles and their arrangement relative to each other will just quickly determine the gloss level. Very small particles span of ag glass – equivalently very tight, gentle features, or deep, wide features – mean very high gloss, because the specular reflection predominates. Very large particles span of ag glass – i.e. very deep, wide features, very low gloss because diffuse reflection takes hold.

Where the etching is very well focused and tightly controlled – the ag glass surface will be smoothly distributed over the entire panel. Where the etch chemistry is inconsistent – cold spot effects, uneven acid strength or uneven dwell time – that random spread of ag glass particles will spawn the often dreaded Sparkle. Sparkle manifests as a regular galore of glittering snow-y surface – and becomes very obvious on 200 plus PPI displays. When the pixel pitch is below the etch feature size, where the etch feature sizes are no longer visible – the otherwise small inconsistencies in the etch pattern may be very obvious as surface graininess.

Very little sparkle will be present if the feature diameters are designed to be below the pixel pitch. For a 27 inch 4K display (roughly 163 PPI, 0.156 mm pixel pitch) – the etch features will have to be generated at an average diameter of less than 80 μm. This ensures the sparsity of the scattering pattern – below the visible threshold.

The choice of material is also important. etch chemistry along the same lines for soda-lime glass and aluminosilicate glass will be very different on account of these substrates’ varied oxide contents. Aluminosilicate glass—which is generally the choice for enhanced scratch resistance—tends to produce a more controlled and finer etch texture than soda-lime, which has a softer and more reactive surface.

The latter requires a somewhat shorter etch time so as not to nosedive past the target roughness. When ordering the etched AG glass, always check which substrate has been planned for by the manufacturer, as the same etch recipe will achieve radically different gloss levels on different glasses.

AG Glass Gloss Ranges by Application: Which Level Fits Your Product?

Choosing the right gloss level is about action frames, not display specs. An anti-glare AG glass window that looks fantastic inside a hospital reading room might melt in front of a bus shelter kiosk. Below is a table illustrating several levels of gloss along with corresponding applications and measurable optical properties of AG glass at each level.

PPI Consideration: Displays with a pixel density over 200 PPI require a gloss level over 70 GU not to Display the place. This is a geometry issue, when etch features are larger than the pixel pitch, they become a tiny lens and send the light from several pixels to the same focal point – producing a grainy place. High resolution displays and custom ag glass solutions require finer place pattern (smaller gloss) to stay under place visibility.

How to Specify AG Glass Gloss for Your Next Order

No matter if you are selecting the reference proposal, the appropriate ag glass for 1 prototype, or scaling to production loads of 10,000+ panels, the specification process is the same five steps. Omitting any of the steps – especially number five – exposes you to the risk of batch rejection when the delivered panel fails to meet requirements.

Interested in matching the best gloss level to your display? If interested in ag glass samples with your target gloss, substrate choice and panel dimensions available to specify, please contact saiweiglass.

Frequently Asked Questions