Struggling with screen glare on your display cover glass? Mis-specifying the anti-glare coating can ruin display clarity and the user experience. Learn the four key tests to get it right every time.

To properly test an anti-glare（AG） coating, you must measure four key optical parameters: Haze, Gloss, Distinctness of Image (DOI), and Sparkle. Evaluating these metrics together ensures you achieve the perfect balance between glare reduction and high display clarity for your custom glass cover.

Many displays are protected by a cover lens. This isn't just a simple piece of glass; it's often treated with special coatings for scratch resistance, anti-reflection, and anti-fingerprint functions. But knowing if your supplier has met the specs, especially for anti-glare, is crucial. Today, I'm going to walk you through the performance indicators for AG coatings. We'll get into anti-reflection (AR) and anti-fingerprint (AF) in future articles.

From light scattering to optical distortion: what are the 4 key metrics to qualify AG on a cover lens?

You're looking at a spec sheet filled with AG terms like Haze¹ and DOI². It's confusing, and choosing wrong leads to a subpar display. Let's demystify the four metrics now.

The four essential metrics for qualifying an anti-glare (AG) coating are Haze, Gloss³, Distinctness of Image (DOI), and Sparkle⁴. These parameters quantify the coating's ability to scatter light, its surface shininess, its impact on image clarity, and any resulting visual graininess or "noise."

In my experience, the core of a good AG coating is creating a micro-scratched or rough surface. This texture scatters reflected light, which is what eliminates that annoying mirror-like glare. However, this same texture can interfere with the light coming from the display itself. To find that perfect balance, manufacturers and engineers need a common language. That language consists of four key parameters. When you specify an AG coating, you're really trying to find the ideal formula by adjusting these four variables to match your display. Let's break them down.

AG Performance Metrics Explained

Why isn’t higher haze always better for balancing AG performance?

You asked for high haze to kill glare, but now your screen looks foggy and washed out. Chasing a single metric is a common trap. Let's find the sweet spot for a crystal-clear display.

Higher haze isn't always better because excessive light scattering degrades the display's own image quality. Once haze exceeds a certain threshold (e.g., >20-30%), it causes noticeable fogginess, reduced contrast ("washed out" blacks), and a shimmering sparkle effect, ruining visual clarity.

I’ve seen clients fall into this trap many times. They think that since haze reduces glare, maximum haze must be the best solution. That’s rarely true. Technically, transmission haze is the percentage of light that, after passing through the glass, scatters more than 2.5 degrees away from its original path. A higher percentage means more scattering and a stronger anti-glare effect. However, haze has a "comfort zone" and significant side effects. When you push it too far, especially on high-end touchscreens, you create new problems.

The Problems with Excessive Haze

• Optical Distortion: The whole screen can appear "whitewashed" or foggy. Small text and icons lose their sharp edges and can appear to have a soft halo around them.
• Increased Sparkle: The AG texture can interact with the pixel grid of the display, creating a distracting grainy or shimmering effect. I’ll discuss this more later.
• Lower Contrast & Readability: The display's black levels suffer, making them look like dark gray instead of true black. This ironically can make the screen less readable in bright light, defeating the purpose of the anti-glare coating.

How do you stop guessing and use DOI and Sparkle to define AG quality?

Your cover glass has the target haze, but it still looks grainy or distorted. You're missing the two final quality checks. DOI and Sparkle are the metrics that matter for premium products.

You use DOI and Sparkle to judge the trade-offs of the AG coating. DOI directly measures reflection clarity; a moderate value (e.g., 20-40) is good. Sparkle measures visual noise; it must be low for a clean image. These two metrics define a high-quality, premium finish.

Here’s the practical advice I give to all my clients: Start by setting a target haze range (for example, 10-18% for a high-end touchscreen), not a single number. Once you're in that range, shift your focus to DOI and Sparkle. These two parameters are often the real bottlenecks for achieving a premium look and feel, and they reveal a manufacturer's true process control.

DOI: Finding the Right Amount of Blur

DOI directly measures the quality of a reflected image. High-performance touchscreens shouldn't have a perfect mirror reflection, but you also don't want the screen content to become blurry. A moderate DOI (often 20-40) is the sweet spot. It's enough to blur distracting reflections without distorting the actual display image underneath.

Sparkle: The Premium Killer

Sparkle is that "sandy" or "glittery" texture you see on some AG screens. It’s a huge distraction and makes a product feel cheap. Minimizing sparkle is non-negotiable for a premium device. This is controlled by carefully tuning the manufacturer's etching or spray coating process (controlling the particle size and uniformity) or by using specialized anti-sparkle additives in the coating formula. A supplier that can deliver low sparkle at your target haze is a supplier you can trust.

Conclusion

Testing AG coating isn't about one number. It's about balancing Haze, Gloss, DOI, and Sparkle. This balanced approach ensures you eliminate glare without sacrificing the brilliant clarity of your display.