Monday, November 1, 2010

A New Metric for Smartphones

Everybody loves a great design, everybody loves designs that do what they're supposed to do, and do it well. Sometimes coming up with a great design is easy and sometimes it is hard. It's hard when there are conflicting design goals; for instance an airplane has to be light, but it also has to be strong. These goals conflict and finding the optimal balance of strength and weight is perhaps the primary problem an aerospace engineer (an "AE" as they were called in undergrad) faces. Similarly, smartphones also have a conflicting set of design imperatives. They must be small, but they also must display a lot of information and be great web browsers and media viewers. 

Being great browsers and media viewers requires a large screen, but having a large screen conflicts with the design imperative to be small. For the AEs, the solution to their strong-but-light dilemma is the use of efficient structures and efficient materials, which means those materials/structures possessing a high strength/weight ratio. For smartphones the solution is also to be efficient but instead of with weight, with existing surface area. For this reason I decided to calculate the ratio of screen area to total surface area for a number of phones to see what kind of progress we've made in how efficiently our phones fill out their dimensions with big beautiful screens. The factors affecting this ratio are generally:

1. General Design
2. Screen Size
3. Screen Aspect Ratio (shown in bold light grey)

The Android handsets are evolving the fastest and should offer a good look at where we're going. Let's take a look at three milestone (pun intended) Android devices. The ratio of screen-area:total-front-of-phone-surface-area is in orange; I'm going to call it "Areal Efficiency" or "AE" for short.

Phones scaled to equal height

I chose the G1 simply because it was the first Android handset ever, the Droid because it's launch was Android's true coming-of-age, and the EVO partially because it remains (in my opinion) one of the best spec'd android phones out there and partially because I suspected it would score very well in the areal efficiency dept. As you can see the trend appears to be solidly in the right direction, areal efficiency is going up; though unfortunately we'll see later that it's not as clear cut as these three phones make it appear, more on that later but for now lets move on to Android's stiffest competition and the device that ushered in the era of truly smart phones, the iPhone. 

While there are numerous makers of numerous Android handsets there is only one maker of iPhones, and only one new model comes out per year (until this year if the rumors regarding a VZW iPhone finally pan out). Apple is, of course, that maker and they appear to be committed to a fixed screen size and are definitely committed to supporting only one aspect ratio. These self imposed restrictions handicap the advancement of areal efficiency but are there for generally good reasons which we'll explore below. First let's see how the iPhone(s) does in the areal efficiency metric.

Not great but considering that it launched a year before the G1 this is yet another metric that shows the original iPhone to have been ahead of it's time though perhaps the mold was frozen a little too quickly.

Screens have a minimum bezel, that is the screen itself must extend beyond the actual pixels in order to function properly, reducing this bezel is no doubt one of the design goals of screen manufacturers but currently it requires all phones to have dead space between the edge of the screen and the edge of the phones surface as shown by the red line on the left edge of the iPhone 4 image, this (and other practical matters) limit the maximum areal efficiency of all phones to a value below 100%. This bezel does not scale linearly with the screen size however and so the bigger the screen the higher this maximal value of AE is. Apple's choice of a 3.5" screen seemed generous in 2007 but now seems rather small, this relatively small screen size is likely limiting the iPhone's areal efficiency to some degree. On top of screen size, there is also an optimal shape for phones and achieving it is also limiting Apple, lets take a look at how the basic aspect ratio (y dimension over x dimension) of the phone has evolved in the last few decades:

Obviously not to scale

The green outline is to highlight aspect ratio; when phones became mobile they became smaller because (of course) people had to carry them everywhere, but the aspect ratio generally stayed the same until the advent of smartphones when it decreased fairly dramatically. Having a screen with a standard aspect ratio (4:3 or 3:2 in that day) was probably a driving factor in decreasing overall phone aspect ratio and while there is room for further reductions in aspect ratio most manufacturers wisely seem to be preventing their devices from becoming too square. Apple likely has this in mind when designing the iPhone but their chosen aspect ratio of 3:2 has had (what I imagine is) an unintended consequence. In order to prevent the device from being too square, the iPhone has a lot of dead space on the top and bottom that could be filled by more screen but is not, the vertical height of the iPhone's single button creates it at the bottom but there is nothing save perhaps design aesthetics necessitating it at the top. Maintaining the screens aspect ratio is critical for the  continued backward compatibility of apps on the iPhone so future advances in areal efficiency will have to come from eliminating dead space on the sides and top/bottom, I believe Apple has already cut the distance from side-of-screen to side-of-phone to the minimum possible with the iPhone 4 (they've reduced it to a lower point than any other phone I'm aware of save perhaps the HTC Aria) so it will be interesting to see if Android or WP7 handsets really apply any pressure to Apple by achieving consistently high areal efficiency.

Back to the original Android handsets, from the three given it appeared that we were headed straight in the right direction but launches since the EVO have all been steps backwards. Here's a graph:

As you can see, AE peaked with the EVO and has declined since, I had high(er) hopes for the Droid X because it's hardware buttons allow extra space to be saved below the screen relative to the standard capacitive buttons but any savings were lost by including a wide strip above the hardware buttons that displays the VZW logo, despite this, Droid X scores second place out of all handsets. Also mildly disappointing was the Galaxy S line from Samsung which, while they are great phones, would have been better if they wasted less surface area, they unnecessarily mimic the symmetrical dead space areas on the iPhone's top and bottom without also mimicking the iPhone's thin side bezel and are put to shame by Motorola's Defy which is water-resistant, shock-resistant and beats Samsung's 4" screened offerings (AE 58.91%) with an AE of 60.55% on a 3.7" screen. It is possible that hardware constraints unknown to me are reducing AE on these two models but I rather doubt it as circuit boards that have very similar requirements to those of the Droid X or Galaxy S are currently being stuffed into much smaller designs such as Sony's X10 mini. While the Galaxy S and Droid X are a little worse than they could be the most egregiously inefficient design I've seen so far is Samsung's dual screen prototype. Honestly when the primary screen is ("super") AMOLED and you can shut off however much of it you like (making It smaller and reducing it's power draw) having a second screen is entirely pointless. This design annoyed me so much that I thought to myself "there should be some design metric that prevents companies from wasting time on such crappy designs so they can spend more time on good designs"... well here it is.

Just to show that maybe consumers have intuitively picked up on this metric without having consciously quantified it and to show that OEMs should probably be aware of it regardless of what some nobody writes in his blog let's add the iPhone to the above graph of Android handset AE values:

Coincidence that the first Android phone to be truly competitive with the iPhone was also the first one to exceed iPhone's AE? I would say only partially coincidental. Also perhaps indirectly indicative of this metric's possible significance is that Android's top two selling handsets are also one and two in terms of AE. I certainly don't think that making AE ubiquitous is going to change too much but I do think that if smartphone OEMs were a little more conscious of wasting surface area we'd all have slightly better phones.

In conclusion the whole point of this blog post is to make smartphones better, we consumers can have a say in smartphone design if we give the OEMs feedback and apply a little pressure, the best way to do that is to get review sites to grade each phone on relevant metrics, currently they are not graded on areal efficiency but if they were I think it would ultimately result in better designs and happier consumers.

Click here to send review sites an endorsement of AE as a smartphone metric.

Click here to sign a petition to get it included.

If you want to see the exact numbers used to calculate AE values or calculate your own here is the Excel spreadsheet.


  1. Word has it the Samsung Continuum (the "dual-screen" phone) does indeed have one large screen, just divided into three regions. So possibly future software would allow that whole area to be used to display web pages or other information.

    Also should your metric count space used on the face for other useful purposes? Obviously a (traditional) Blackberry scored horribly in this metric, but as the keyboard and other buttons are indeed useful to a lot of people they shouldn't necessarily be counted as dead space. Same goes for the buttons on Android phones. Would be nice if the Droid X was shorter than the Evo 4G, though being thinner through much of its body might result in a flatter battery which moves all the PCBs out further.

  2. Of course I'm not trying to say that this is the only relevant metric of design, the Continuum will appeal to some people and we do now know that it is just one screen with soft keys sort of silk-screened on to the "middle", but I think the conventional layout with softkeys below is clearly superior as you could still have a ticker but it wouldn't be separated from the rest of the screen so you could use those other pixels for other tasks. Also I don't think that 100% would necessarily be the optimal AE value for a device, I would certainly want to keep some Droid X like buttons below the screen in any case and you gotta have a mic and speaker somewhere.

    Regarding Blackberry, yes the space the keyboard occupies is not wasted but I think the iPhone proved that it is not being optimally used either. Consumers have spoken with their wallets on this issue which is why I don't believe the Droid Pro will enjoy sales as strong as other high end Moto models.