Smart phone power performance has improved dramatically in recent years with significant improvements in processing power, wireless power, and display power efficiencies. These gains have been achieved as growing consumer preference for larger smart phone screen sizes has also conveniently provided larger form factors to accommodate higher battery capacity. Battery technology has not necessarily improved significantly during this time – most gains or perceived gains are associated with system-level improvements.
The iPhone 4 had a 1,420 mAh lithium-ion battery while the current iPhone 14 Pro Max has a 4,323 mAh lithium-ion battery, more than tripling the battery capacity, a trend that is fairly representative in mobile devices where autonomy is a requirement, if not a top priority among end users.
Similarly, wrist-worn devices have also improved from < 24 hours of usable battery life, to multiple days of battery life. These gains, too, have come from system-level improvements in processing, wireless, display, dynamic power management as well as larger form factors that allow higher capacity batteries (IE, Apple Watch Ultra).
Today, as various technology providers turn to higher-consumption augmented reality (AR) as the next wave, designers and engineers can’t expect that consumers and other users in industrial and commercial sectors will tolerate an increase in size or weight to accommodate greater battery capacity. No matter the user, fatigue, strain at contact points, and greater heft leads to low adoption, low utilization, and overall poor product acceptance. This is particularly critical in use cases that involve a high degree of mobility or activity. In today’s increasingly mobile and agile world, in fact, anything that limits mobility for the consumer, no matter how seemingly technically advanced, would immediately be deemed a novelty, not something with the potential to be a widely-adopted standard.
First, AR smart glasses will necessarily incorporate some type of display, requiring, at the very least, a processor, battery, and some type of connectivity, most likely provided by a wireless chipset.
Next, regarding functional requirements, an AR smart glass display must have clarity and be bright enough to use in ambient daylight, with an overall form factor that remains light enough to use regularly in tandem with a smart phone or a smart watch. Our internal research indicates that while it might be possible to transform a mobile device into eyewear, a 100g, 75g, or even 50g device will not be light enough for routine, full-day use. Devices that attempt to deliver more features/functions with complete autonomy will pay a weight penalty and will therefore be limited to occasional or intermittent use, resulting in a self-defeating design choice.
Therefore, the two most critical attributes to widespread AR acceptance and adoption are long battery life and light weight. And, unfortunately, these attributes are in direct opposition.
Long battery life, or “autonomy”, goes hand-in-hand with all-day use. From a convenience standpoint, smart eyewear should have similar power performance to the smart phone or smart watch, i.e., requiring a charge once a day or less. Past technology vendors learned the hard way that devices with poor autonomy are often abandoned, simply due to inconvenience. If AR is to be the next great frontier, then autonomy must meet or exceed consumer expectations established by smart phones, smart watches, and other wearable peripherals such as ear buds.
Low weight is essential for all-day or repeated extended use. If we assume that AR eyewear will complement the smart phone and/or the smart watch, then we must assume that it must be comfortable enough to wear continuously if not frequently – on and off throughout the day – also, like the smart phone, smart watch, or ear buds.
In fact, independent studies have shown that eyewear must be 40g or less to achieve high user acceptance (Wearing Comfort and Perceived Heaviness of Smart Glasses, YMKim, 2021). This 40g threshold poses a very specific challenge to AR eyewear developers: how to deliver a complete eyewear and technology package (processor, display, battery, wireless chipset) under 40g when many “standard” eyewear styles, absent any tech, are in the30-40g weight range?
Another AR eyewear-specific requirement is clear display visibility in ambient daylight conditions. However, the greater the level of brightness the more power is consumed. One of the reasons many of the AR products that have appeared to date have either incorporated high capacity batteries, (often with just a few hours of usable operation time), or employed an external power supply to shift weight away from the user’s face, (via a power cord to connect eyewear to a remote power source), is to accommodate this higher power demand.
The goal should not necessarily be to deliver the brightest possible display, but to rather deliver a display that functions well in a wide range of conditions, without unwanted or unintended side effects such as retina burn-in, distraction from, or interference with, the normal field of view.
Finally, form factor is essential. Prospective AR vendors and customers alike appreciate the importance of design, as illustrated by Apple, Samsung, and other design leaders. However, AR eyewear is new territory. Legacy eyewear vendors aren’t necessarily the best references: there are no hard rules in fashion, and eyewear is arguably an extension of the fashion industry, dominated by manufacturers who mainly sell eyewear styles under license from fashion brands. Styles can be bold and conspicuous – in other words, heavy – and still be successful. Other styles might feature advanced materials resulting in a lighter weight. But AR eyewear cannot afford to take both fashion risks and technology risks, while also addressing the practical and functional limits imposed by weight. For this reason, AR eyewear must aim to make the technology components as light, small,and inconspicuous as possible, in order to easily integrate with accepted eyewear styles and achieve user acceptance.
One might notice that Meta seemed to apply this principle to their Stories effort, by choosing to ensconce the tech package within Ray-Ban frames: iconic and stylish designs, and designs that offer a relatively large mass within which to conceal technology components. In the case of Stories that included cameras, a processor, a battery, a wireless chipset but no display.
We’ve already seen the backlash to the design approach that says that AR should have an appearance of “cyborg” or “science fiction” or “military” or “gamer”. On the contrary, any AR eyewear form factors intended for widespread adoption must be as close to “normal” eyewear as possible and AR technology must be readily incorporated into those existing styles.
AR eyewear asks consumers to try something new, and necessitates a change in behavior in the process. Behavior change is possibly the single biggest hurdle in the adoption of new tech. Therefore, anything an AR eyewear vendor can do to minimize this obstacle will pay dividends in terms of market acceptance.
Beyond a general requirement to meet consumer preferences, there are certain use cases where low weight is essential. Not coincidentally, many of these use cases also benefit from seeing external data in real-time.
Consider sports use cases such as running. Athletes are increasingly dependent on devices to track and record a wide variety of performance metrics: speed, pace, heartrate, power, and more. For marathoners, a frictionless virtual pace setter or "ghost runner" can be a clear strategic advantage. The world record holder and only person to run a sub-2 hour marathon, Eliud Kipchoge, famously used a laser-guided pace setter to train and to achieve the record, and most major marathons include formal pace setters as part of the race experience. Managing pace, or more broadly, effort, is the dominant strategy in many different types of endurance events. In addition to pace, real-time heart rate and power data are also used to help manage effort during endurance events.
The key is continuous, in-activity monitoring. It’s not practical or in any way advantageous to use heavy eyewear in a marathon to try and achieve this. First, runners require the lightest weight possible in order to avoid “bouncing” associated with eyewear that’s greater than 40g, as well as to have stability and comfort for extended use. Then, the benefits associated with a light-weight data projection in the natural field of view become clear: focus remains on the course ahead, improving situational awareness and safety; the need to break stride, slow pace, or change body mechanics to view a wrist-based display is no longer necessary; anxiety and device dependency is reduced; and easily and intuitively glanceable data in the natural field of view provides the most frictionless training experience possible.
All of these benefits, otherwise unavailable, contribute to performance gains that are clearly measurable over the course of a marathon. Without the lightweight profile, there is no legitimate chance to bring the benefit of AR to the athletic segment.
Use cases where “real-time information at a glance” may be a meaningful advantage including running, cycling, triathlon, Nordic skiing, and swimming – all activities which depend on management of effort - pace, power, heart rate, etc.. In these use cases, light weight is not merely preferred, it is required. By extension, there are many more athletic and other practical use cases which also benefit from light weight: from niche sports such as parasailing or kiteboarding, to warehouse and delivery and security applications that call for all-day, always-on functionality.
Once weight reduction and therefore comfort have been achieved, extended use is possible, but only if battery life can meet the use case demand. This standard applies equally to competitive ultra-runners who require comfort and stability for all-day events,as well as for industrial applications in which the basic power requirement maybe to meet or exceed run time for a standard 8-hour shift.
In this sense, ultra-runners, warehouse workers, delivery drivers, and many others all expect and indeed require comfort and autonomy that matches the demands of their activity. While AR will certainly be deployed across a wide range of consumer and industrial applications with many unique requirements, it is clear that many applications have a common minimum requirement for autonomy that is much greater than just a few hours.
In the most basic sense, broad market adoption of AR requires “all-day” battery life.
In every class of device, the battery is one of the heaviest individual components, if not the heaviest. This mass is more manageable in smart phones and tablets as form factors have gotten larger, but as devices become smaller with distinct size constraints (IE watches, earbuds), the area or volume available for batteries is limited. We become acutely aware of this constraint when considering AR eyewear, in which sub-40g weight is essential, and style is a priority.
As battery size increases, so does the size of the battery’s enclosure, resulting in a kind of “double penalty” when it comes to weight gains.
Weight distribution of the various components in typical AR smart glasses illustrates the need to make no compromises to meet acceptable functional and ergonomic requirements. The implication is that battery weight, therefore, cannot exceed a few grams, especially for all-day autonomy and/or high-performance applications.
To stay within the 40g acceptable ergonomic weight limit of AR smart glasses, system designers need to look closely at the power consumption of each individual component, and target an overall power consumption of 10-30 mW.
The foremost design implications are:
· Use a low power CPU (5-10 mW): this limitation suggests that processing should be offloaded to a companion device such as a smart phone or smart watch.
· Minimize radio traffic (BLE power consumption is ~15mW ): consider “bit-trickling” strategies rather than full-throttle data streaming.
· Use a low power display; display technology can have a dramatic impact on overall system power demands, IE: low power µOLED 1-5 mW; standard µOLED and µLED 50-100mW (or more for color µLED); Laser-Based Scanning >300mW
At MICROOLED, we’ve been creating cutting-edge near-eye AMOLED displays and modules for a wide range of products for decades. We are engineers and, by extension, problem-solvers, and we approach each problem using what tools we know best: physics, science, facts.
We were intrigued by the array of problems that tech companies seemed to be coming up against in various efforts to bring a useful and usable AR eyeglass solution to market. In analyzing the issues holding the sector back from widespread adoption we were able to pinpoint the core issues and leave the secondary issues aside.
In the absence of dramatic new battery technology with higher energy density at relatively consistent volume, we determined that prospective AR vendors need to look beyond obvious power management schemes found in other contemporary wearable technology products.
For the foreseeable future, a return to highly refined and efficient designs may be the only way to meet requirements as well as user expectations.
As shown above, the combination of highly efficient µOLED display tech with minimal processing and radio overhead can deliver system solutions in the < 30mW range.
MicroOLED’s display technology and open ActiveLook platform have already delivered solutions that provide exceptional performance with up to 12 hours of battery life for a wearable display that weighs just 36g – total.
This is the lightest AR solution, with the longest battery life available today – and the first solution viable for use in endurance sports.
