If you have ever wondered how AR glasses work, the short answer is that every pair has to solve one awkward problem. They must add digital images to what you see without blocking the real world. There are three main ways to do it, and the one a company picks decides how thin the glasses are, how bright the picture looks and how much they cost.
The two ingredients
Every pair of AR glasses has a light source and a way of delivering that light to your eye. The light source is a tiny display, often called a light engine, built from technology such as micro-OLED, micro-LED or LCoS. The delivery system is the optics, and this is where the three approaches split.
Birdbath optics
Birdbath designs fire the image from a small display onto a curved, partly mirrored surface in front of your eye. That surface reflects the digital image towards you while still letting light from the real world pass through. The result is usually a bright, sharp picture at a lower cost. The trade-off is bulk. The optics need space, so birdbath glasses tend to look chunkier than ordinary spectacles, and the tinted combiner makes the real world look slightly darker.
Waveguides
Waveguides are the approach most people picture when they imagine everyday AR glasses. A projector at the edge of the lens injects light into a thin sheet of glass or plastic. The light travels along the sheet, bouncing between its surfaces, until tiny structures steer it out towards your eye. Because the lens itself does the work, waveguide glasses can look close to normal eyewear. The difficulty is manufacturing. Waveguides lose a lot of light along the way, can show uneven colour, and make it hard to offer a wide field of view, which is why they are expensive.
Video see-through
The third approach does not let you look through anything. Cameras on the front of the device capture the world, and screens inside show you that live video with digital objects blended in. It is the method headsets such as Apple Vision Pro use. It gives the software complete control, so digital objects can hide behind real ones and the view can be as bright or as wide as the screens allow. The costs are weight, battery drain and the need for very low delay between what the cameras see and what your eyes are shown.
What to look for as a buyer
Field of view, brightness, weight and battery life all pull against each other. A wide, bright picture needs more optics and more power. A slim, all-day pair has to settle for a smaller window. When you read about new AR glasses, ask first which of the three methods they use, because it tells you most of what you need to know about what they can and can’t do.
Our take
At AugmentedReality.com, we think this is the most useful thing to understand before reading any AR hardware announcement. Most headlines talk about price or brand, but the optics decide what the product is actually like to wear. Waveguides are where the industry is heading for everyday glasses, and the companies that make them cheaply and brightly will shape the market.