The floodgates for the next major smart device revolution are opening. And unless you have been living under a rock you already know that this time it's a smart watch, a long overdue update to what is essentially 19th century wristwatch technology. There are already a fair number of early players in this new category -- in this article we'll examine how well the displays in two second generation smart watches from two top tier manufacturers perform: the Sony SmartWatch 2, with an LCD display, and the Samsung Galaxy Gear 2, with an OLED display.
Smartwatches are the next revolution in tech gadgets because a watch should be able to tell you a lot more than just the time. Plus, smartphones are now so important and doing so much that they need a readily assessable and conveniently viewable assistant to help out with all that's going on in the smartphone -- a smart watch is perfect for this and your wrist is prime coveted real estate. So if you get lots of text messages, emails, appointment and app alerts, or even voice calls, then a smartwatch will be very useful and helpful. It's no surprise that most of the major mobile tech players are expected to compete in this new category, including (alphabetically) Apple, Google, LG, Motorola, Qualcomm, Samsung, and Sony.
The display is clearly the most important and key component in a smart watch and most people will expect a smartwatch to have a display with quality comparable to their smartphone.
That turns out to be a major challenge for a number of reasons. First, the screen size is only about 1.5 inches, so the display needs a fairly high resolution in pixels per inch in order to provide sharp and easy to read fine text and graphics. It also needs to produce fairly bright images because watches are often viewed in high ambient light. A larger colour gamut is also needed to counteract colour washout from ambient light, plus vibrant saturated colours are quite helpful when reading screens with text and graphics information. A major challenge is accomplishing all of this with greater than one day of battery running time.
The software will be updated but the display cannot.
The software OS, user interface, and apps for smartwatches are evolving and improving rapidly, so it isn't necessary to wait for completed and polished software before buying one -- but the display cannot be updated so select it very carefully. We won't be discussing the software here, just the display. You'll find lots of software and app reviews and articles elsewhere, but we'll provide an in-depth analysis of smart watch displays that you will find nowhere else.
Smartwatch display technologies
Almost all current smartphones use a backlit LCD or an OLED display -- both require battery power to generate their light. They will also work in a smartwatch provided the display is on only when you need to look at it -- just like a smartphone. That can be done with a manual on button, a touchscreen gesture, or by monitoring the motion and position of the watch and then automatically turning the display On when it is moved to a viewing position. That's how the Samsung Gear 2 OLED display works. Another approach is to use a reflective display, which can use existing ambient light to keep the screen working and visible at all times without a significant power drain -- only requiring an internal light in reduced ambient light conditions. Qualcomm's Mirasol colour display works that way (although the Colour Gamut is subdued). LCDs can also be manufactured with a pure reflective mode (like traditional LCD wrist watches), or with a combination of both a backlit transmission mode and a reflective mode, which is called a Transflective LCD. That's how the Sony SmartWatch 2, Pebble, and Pixel Qi displays work.
The Display Shoot-Out
Here we will test the Sony SmartWatch 2 and the new Samsung Gear 2. In the near future we'll do a Multi-Display Technology Smartwatch Shoot-Out. To examine the performance of the Sony SmartWatch 2 and Samsung Gear 2 displays we ran our in-depth series of Mobile Display Technology Shoot-Out Lab tests and measurements in order to determine how the displays performed. We take display quality very seriously and provide in-depth objective analysis based on detailed laboratory tests and measurements and extensive viewing tests with both test patterns, test images, and test photos.
Overview of the Samsung Gear 2
The Samsung Gear 2 has a 320x320 pixel 1.63 inch RGB Stripe OLED display, touch screen, accelerometer, gyroscope, home button, 2 MP camera, 4GB memory, microphone, speaker, vibrate function, IR LED to act as remote control, heart rate monitor, charging cradle, and Bluetooth communication. The watch is IP67 dust- and water- resistant (up to 30 minutes in one meter of water). It runs under the Tizen OS and works with the Samsung Galaxy S5, Galaxy S4, Galaxy SIII, Galaxy Note 3 and Galaxy Note 2 Smartphones. The user interface is already fairly nice. Samsung provided DisplayMate Technologies with a production unit to test and analyse for this Display Technology Shoot-Out article.
Overview of the Sony SmartWatch 2
The Sony SmartWatch 2 has a much lower resolution 220x176 pixel 1.60 inch Transflective LCD display, touch screen, home button, Ambient Light Sensor, vibrate function, micro USB charge port, NFC and Bluetooth communication. The watch is IP57 dust- and water- resistant (up to 30 minutes in one meter of water). It works with any smartphone running Android 4.0 or later. The user interface is currently quite primitive, but presumably will improve in future updates and upgrades. We purchased this unit retail.
In this Results section we provide Highlights of the comprehensive Lab tests and measurements and extensive visual comparisons using test photos, test images, and test patterns that are covered in the advanced sections. The Lab Tests and Measurements Comparison Table section summarizes the Lab measurements in the following categories: Brightness and Contrast with Ambient Light, Colour Gamut with Ambient Light, Screen Reflections, Viewing Angle Variations. You can also skip these highlights and go directly to the Conclusions.
Battery running time
The small size and weight required for a watch means the battery power is strictly limited. The big question is how long will any particular smart watch run on battery before needing recharging (from either AC or a supplementary battery pack). That will vary considerably based on how frequently a consumer uses it, and the particular Apps that are selected -- for that reason we did not test the battery running time for this article. Because of the wide range of consumer uses, multiple display technologies will be needed for smart watches. Conserving and efficiently using battery power and extending the running time involves a number of different approaches and compromises for the displays on smart watches, which we discuss below.
Display performance specs
The Lab Tests and Measurements Comparison Table has a detailed set of display specs and measurements.
Sharpness: A major difference between the two displays is their screen sharpness: the SmartWatch 2 has a 220x176 pixel screen with 176 ppi and 39K total pixels, while the Gear 2 has a 320x320 pixel screen with 278 ppi and 102K total pixels. The SmartWatch 2 screen was visibly coarse and heavily pixelated (even visible in large text) made worse with poor anti-aliasing, plus the small pixel aperture ratio needed for a transflective LCD makes it much more noticeable. On the other hand the Gear 2 OLED RGB Stripe display was very sharp, even with fine text and graphics.
Brightness: Both displays are fairly bright: the SmartWatch 2 has 495 nits while the Gear 2 has 415 nits in Outdoor mode and 296 nits in Standard mode (Level 5). However, at typical viewing angles (discussed below) the Gear 2 is brighter.
Colour Gamut and Saturation: The Gear 2 has a very wide colour gamut, 135 per cent of the sRGB / Rec.709 Standard, which I normally don't like, but on a small 1.6 inch screen the additional colour saturation is not objectionable, and actually compensates for the reduction in colour saturation caused by ambient light. So under typical ambient light viewing conditions the Gear 2 colour gamut is close to 100 per cent. The SmartWatch 2 has a 91 per cent colour gamut, but it falls drastically with ambient light, and the screen is monochrome in reflective mode.
Colour Depth: In order to reproduce images well a display needs to be able to display a wide range of intensity levels -- most good displays provide 256 intensity levels, which is essential when mixing the red, green and blue primaries to produce all of the necessary on-screen colours. The 256 intensity levels produces 24-bit colour. The Gear 2 display has excellent 24-bit colour. Sony specs the SmartWatch 2 display at 16-bit colour, which has only 32-64 intensity levels, which produces noticeable artifacts in images that have a range of intensities. In a small 1.6 inch display that would normally be fine, but our test images shown below indicate only 16 intensity levels, which is 12-bit colour -- the lowest I have seen in a very long time, and is simply unsatisfactory as shown next.
A good way to evaluate the display and compare the image and picture quality is with screen shots of a number of test patterns and test photos on each display. We have included three below: a DisplayMate test pattern with smooth white, red, green and blue intensity ramps, a NASA spacecraft photo of a Sunset on Mars, and a Sony Xperia demo photo. Note that the images and displays all have varying aspect ratios. The display on the Samsung Gear 2 accurately and nicely reproduced all three images. The display on the Sony SmartWatch 2 produced poor to horrendous versions of the images, with considerable false contouring and related artifacts, which were quite noticeable even on its small 1.6 inch screen, demonstrating some of the display issues that are discussed above and in the Lab Tests and Measurements Comparison Table. While two of these images are challenging, many of Sony's own set of (soft) demo photos had easily noticeable image artifacts. Even if you are not interested in looking at photos on your smart watch (it's nice for quickly showing some family photos) these test images demonstrate important display performance issues.
While we are all used to having the time always visible on a mechanical wrist watch, that seems hardly necessary for a smart watch, particularly with motion and gesture sensors to automatically turn on the display when the wrist is moved to a viewing position. The always on reflective displays each involve selective performance compromises such as reduced image contrast, colour gamut, viewing angle, resolution, and intensity scale, and slower response time. Using a combination transmissive and reflective LCD seems like a good solution, but it comes with a significant performance penalty in both the backlight transmissive mode and the reflective mode that keeps the always on image visible in moderate ambient light, and in many (but not all) high ambient light situations (see below). It remains to be seen how consumers will respond and decide which compromises are tolerable or necessary, so multiple display technologies will undoubtedly be needed for smart watches..
Performance in high ambient light
Smart watches are likely to be used more often in higher overall ambient light than smartphones, so how the screen visibility and readability are affected by ambient light is extremely important. Ambient light washes out the screen colours and image contrast. There are a number of ways to improve display performance in ambient light: the two best known are increasing the screen brightness and reducing the screen reflectance. Another is to use extra saturated primary colours and dynamic image contrast to counteract the image washout. But high ambient light will at some point overpower all emissive displays like LCDs and OLEDs. One additional important viewing strategy that we all do automatically is to adjust the angle and position of our wrist to improve watch visibility, and if necessary also rotate so the watch is in our shadow. That works quite well in most circumstances, except in places like the beach.
Reflective displays use an entirely different approach by proportionally reflecting the ambient light, so they have a fixed Contrast Ratio (42 for the SmartWatch 2), and in principle are viewable for any level of ambient light, no matter how high. However, one major enemy for all displays, including reflective displays, are mirror (specular) reflections that overlay the display image with distant images that are reflected by the upper layers of the screen. The only solution is again to vary the angles and positions as mentioned above.
In its Outdoor mode the Samsung Gear 2 display was readable and usable even in fairly high 40,000 lux outdoor ambient light, but not in direct sunlight. Its strong saturated primary colours also improve high ambient light readability. The Sony SmartWatch 2 display was also very readable at 40,000 lux and above, and even in direct sunlight in its reflective mode. However, for both watches the mirror reflections mentioned above require the display to be carefully oriented to avoid imaged reflections (including possibly your face). See the Brightness and Contrast with Ambient Lightand Colour Gamut with Ambient Light sections for details.
Performance with viewing angle
Almost all displays and display technologies look best when viewed straight on with a zero degree viewing angle -- and that's how most people try to view their smartphones, tablets, notebooks, monitors, and TVs. However, a watch is attached to your wrist, which can only move in a constrained manner, so most of the time it's easier, more convenient, and more comfortable to hold it at an intermediate viewing angle like 30 degrees. At that viewing angle the Brightness of most LCDs falls by over 55 per cent, and the Contrast Ratio falls even more, by over 75 per cent, while OLEDs experience only a 20 per cent decrease in both. As a result, the SmartWatch 2 LCD display has a drastic performance decrease at typical viewing angles, but the Gear 2 OLED display experiences only a relatively small one. While the SmartWatch 2 is considerably brighter at 0 degrees, the Gear 2 is brighter and has a much higher Contrast Ratio at typical viewing angles. See the Viewing Angle Variations section for details.
The performance differences between the displays in these two top tier second generation smart watches are surprisingly quite large. The OLED display on the Samsung Gear 2 performed very well across the board, almost identically to the most recent Galaxy S OLED Smartphones in almost every test measurement and viewing category. It looked and performed like a small version of a high quality OLED smartphone display -- including sharpness, high pixels per inch, brightness, colour depth, colour gamut, viewing angle, in ambient light, and overall image and picture quality. For details see the Lab Tests and Measurements Comparison Table and also the screenshots above.
On the other hand, the Transflective LCD display on the Sony SmartWatch 2 was quite disappointing across the board, especially for a second (actually third) generation device. To easily see that examine the mediocre to poor results in the detailed Lab Tests and Measurements Comparison Table and also in the screenshots above. In particular, the coarse and heavily pixelated low resolution and low pixels per inch screen made worse with poor anti-aliasing, the very low colour depth, the poor colour gamut in ambient light, and also the poor viewing angle performance (because watches are not easily positioned for zero degree viewing). Using a combination transflective LCD comes with a significant performance penalty in both the backlight transmissive mode and the reflective mode that keeps the always on image visible in moderate ambient light and in some but not all high ambient light situations. The choices and compromises made by Sony for the SmartWatch 2 display simply do not work well. The (rumoured) upcoming (presumably) LCD smartwatches from LG and Apple will undoubtedly perform considerably better.
The early adopters have been enjoying their smart watches for quite some time. The display is clearly the most important and key component in a smart watch, and the current Samsung Gear 2 already has an excellent display. We'll revisit smartwatch displays again soon when the highly anticipated products from Apple, LG, and others arrive. The software OS, user interface, and apps for all smart watches will continue to improve rapidly with downloadable updates. It will be really interesting to see what other display technologies and strategies are introduced for smart watches, the consumer responses to them, and how they will evolve over time. We'll see more reflective, transflective, curved, and bendable smart watch displays in the near future, and also microLED smart watch displays in the not too distant future. There is no doubt that smart watches will be taking over from mechanical wristwatches, and most likely much sooner than most people think.
Display Shoot-Out Comparison Table
Below we examine in-depth the displays on the Sony SmartWatch 2 and Samsung Gear 2 smart watches based on objective Lab measurement data and criteria. For details and additional information on all the measurements see our Galaxy S5 Display Technology Shoot-Out article. For comparisons with the other leading displays including LCDs see our Mobile Display Technology Shoot-Out series.
Below is a partial excerpt of the table; you can see the full comparison at DisplayMate.
DisplayMate Technologies specialises in proprietary sophisticated scientific display calibration and mathematical display optimisation to deliver unsurpassed objective performance, picture quality and accuracy for all types of displays.