Shining a light on AR ambient dimming
June 20, 2022
I have one of those voice assistant-controlled colour changing light bulbs at home, which is normally just left in 'warm white' state. Or it was, until my four-year-old daughter discovered how to control it. From then on, I’d often hear her shouting “lamp red”, “lamp orange” until she had worked through the colours of the rainbow, and it wasn’t long before long she tried going off-piste with more exotic colours.
However, I noticed her confusion when, during daylight hours, she asked for “lamp black” and to her surprise the light just turned off, instead of producing any black. As a physicist I’m gradually explaining to her that black is the absence of light, so black cannot be produced from the light source.
You may wonder why I am telling you this – and the reason is that it illustrates a parallel challenge in AR headsets that literally lies at the border between the real world and the virtual world.
Blending a virtual image with the real world
Typically, an AR headset works by projecting a virtual image onto the real world, with the aim of blending that virtual image so perfectly with the real world that the brain finds the two indistinguishable. That virtual image is created by a light engine (one for each eye) – essentially a tiny light projector with associated optics within the AR headset, which adjusts the projected image brightness depending on the real-world conditions. This works quite well in low light conditions, but not so well in bright conditions, particularly when the virtual image contains a lot of dark or black areas. The issue is that the light engine cannot produce black – the best it can do is avoid adding further light on top of the already bright sunny day in the background. The result is a substantially reduced contrast of the virtual image – which becomes semi-transparent as the real-world light dominates over the projected virtual image’s lower brightness.
Adjusting the real world’s brightness
What’s needed is the ability to turn down the brightness of the everyday world – either everywhere (global dimming), or ideally, just in the locations where the virtual image is located (local ambient dimming). This can be achieved with a new optical component – a so called pixelated dimmer – that allows the real world’s brightness to be locally adjusted to maximise the contrast of the overlaid virtual image.
FlexEnable’s liquid crystal optics technology uniquely enables pixelated dimming on bioplastic films. At around 0.1mm thick, the pixelated dimmer function can be added with almost no thickness and weight addition to the headset. The film can even be 3D formed to follow to contours of other fixed optical components.
Whilst my lightbulb may well never manage to produce the black that my daughter desires in the real world, we are only just beginning to appreciate the magic that new AR/VR technologies will bring to the virtual world