Global vs pixelated ambient dimming for AR glasses

We compare global and pixelated dimming for AR glasses and the benefits they bring.

Desi Aleksandrova, Marketing Communications Manager

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When it comes to AR glasses, enhancing the visibility and realism of virtual objects is crucial for delivering maximum user experience. Ensuring that images appear solid even as external lighting conditions change, can be achieved by dimming the real world. This dimming enables control of the amount of real-world light that enters the eye and is a feature that’s set to become standard for see-through AR glasses.

Differences between global and pixelated ambient dimming

How you dim the world, globally or at local level (referred to as pixelated or spatial dimming), makes a big difference. Whilst either will increase the contrast of the virtual object, global dimming does this by reducing the luminance of the real world everywhere, even in places where it’s not warranted, potentially compromising the visibility of the real world for the benefit of the virtual. Pixel-by-pixel dimming avoids this trade-off, dimming the real world only behind the virtual object, allowing it to appropriately blend with the undisturbed real-world backdrop.

The table below looks at the main differences between global and pixelated dimming:

Global dimmingPixelated dimming
A single film or filter dims the entire field of view equally.Each pixel of the dimmer can independently adjust its transmittance,
selectively dimming specific areas.
Works everywhere but lacks nuance. Real-world view with very large spatial variation in luminance means poorly lit regions become less visible once dimming is on.Dims bright backgrounds around and behind virtual objects, making them pop and appear more solid, whilst maintaining visibility of even poorly lit areas of the real world.
Can be implemented with existing technologies like LCD shutters or electrochromic films. Switching speed requirement can be relaxed.Requires fast-switching dimming technologies like liquid crystal cells on bioplastic films.
Good for basic AR overlays but struggles in complex environments with diverse lighting.Opens doors for advanced AR applications like seamless blending of virtual and real, true eye-tracking interaction, and hyper-realistic experiences.

In summary, whilst global dimming is simpler and far better than no dimming at all, pixelated dimming is what’s ultimately needed, offering superior visual fidelity and more immersive experiences.

Ambient dimming technologies

Whilst for global dimming there are several candidate technologies, such as electrochromic- and liquid-crystal-based approaches, for pixelated dimming the high switching speed required necessitates a liquid-crystal cell. Pixelated spatial dimming cells of this type could be manufactured on glass, but glass itself is relatively heavy, adding unwanted weight to a device that needs to be as light as possible for comfort and prolonged use (especially as four to eight layers of glass would be needed in each product). As AR optics are typically curved in more than one direction (biaxially), it is also necessary that the dimming cell conforms to the curved fixed 3D optics – beyond what is possible for glass LC cells. Plastic cells are needed to meet the shape, weight and volume requirements for all-day wearable AR devices.

At FlexEnable we have developed the means to manufacture liquid crystal cells on plastic, and the means to pixelate them using organic transistors – also on optically ideal bioplastic films – all the necessary ingredients for spatial dimming on plastic. The result is dimmers that are incredibly thin and light — a single 30-mm diameter dimmer weighs less than 0.3 g and is just 100-µm thick. These liquid crystal cells can be biaxially curved by thermoforming at temperatures that won’t damage the liquid crystal material or the organic transistors. We are excited by the possibility to bring new capabilities to AR, towards the goal of making high performance devices so thin, light and comfortable that they look and feel like regular glasses.

If you are interested to find out more about FlexEnable’s ambient dimming evaluation kits, please get in touch at info@flexenable.com.