Notebooks with Outdoor-Readable Screens in Mid-2007

(May 18, 2007)

by Technology Editor Geoff Walker

A fundamental fact of life in the mobile computing world is that there is very little demand for notebooks that can be used outdoors, so workable solutions are few and far between.  Most of the solutions that do exist are aimed at vertical (specialized) markets such as utility workers or insurance claims inspectors.  This is slowly beginning to change, but we're still very far from any significant mainstream demand for outdoor-readable notebooks. 

 

Outdoor-readability and ruggedness tend to go hand-in-hand, on the assumption that if you're going to use a notebook outside, you're probably going to use it on car hoods, fallen logs, the ground, rocks, benches, concrete structures and in other difficult locations.  Standard commercial notebooks are really quite fragile devices, intended to be carried from place to place in a padded carrying case and then used on a clean flat surface such as a desk or table.  As a result, most of the manufacturers who offer notebooks with outdoor-readable screens do so only on rugged or semi-rugged products.  The only significant exceptions are Fujitsu and HP.

 

There are really only two practical methods of making a notebook screen readable outdoors: (a) crank up the brightness (measured in nits, which is display-industry slang for "candela per meter squared", or cd/m²) to the point where the light emitted by the screen is sufficiently greater than the ambient light reflected by the screen, or (b) treat the surface of the screen so it reflects much less light, which again allows the emitted light to exceed the reflected light.

 

Fujitsu

 

Fujitsu tends to straddle commercial and specialized markets, so they go a little further than most manufacturers in offering outdoor-readable screens on commercial products.  Fujitsu sells several different models of notebooks and Tablet PCs with outdoor-readable screens, using three different types of screens, as follows:

 

(1)  "Indoor only".  This is a standard backlit transmissive TFT LCD with no treatments.  It's just like any other standard notebook screen.

 

(2)  "Indoor/Outdoor" Type #1, identified by Fujitsu as "Ideal for casual outdoor use".  (Note that the "Type 1" designation is my own terminology; there is no standard vocabulary for this subject.)  This is a standard backlit transmissive TFT LCD with a moderate degree of treatment to reduce reflections from the surface.  "Casual outdoor use" is marketing-speak for "barely usable outdoors as long as you shade the screen from direct sun".  The brighter the sun gets, the harder the screen is to read.  Indoors it's great, since all backlit transmissive TFT LCDs these days are excellent -- rich colors, high contrast, bright, etc.

(3)  "Indoor/Outdoor" Type #2, identified by Fujitsu as "Ideal for direct sunlight use".  This is a reflective TFT LCD with a frontlight (FL).  Since the LCD is reflective, the brighter the sun is, the brighter the image on the screen is.  Indoors (used with the frontlight on) it's adequate, with very muted colors, much lower contrast and noticeably less brightness than a typical backlit transmissive TFT LCD.

 

Within these three types of screens, there are the usual variables on which you have to decide depending on your particular application:

•  Viewing angle (super-wide 180-degrees vs. normal ~90-degrees)
•  Resolution (XGA vs SXGA+, etc.)
•  Size (10.4" and up)
  
  

Dell

 

For the last few years, Fujitsu has had the best Indoor-Outdoor Type #1 screen.  But Fujitsu has now been surpassed by Dell, who recently launched the Latitude ATG (ATG stands for "All-Terrain Grade").

 

In my opinion, this semi-rugged Dell notebook has the best outdoor-readable screen of any notebook currently on the market.  The difference is that Dell went further than Fujitsu in reducing the surface reflections.  Specifically (using the T4215 Tablet as an example), while Fujitsu did use anti-reflection (AR) coatings on the top and bottom surfaces of the screen cover as well as on the surface of the LCD, they didn't eliminate the air gap between the screen cover and the LCD.  Total reflectivity on the Fujitsu T4215 is around 1.5% (0.5% top + 0.5% bottom + 0.5% LCD).  In contrast, Dell optically bonded the screen cover to the LCD, which eliminated the reflections from the LCD surface, eliminated the need to AR-coat the bottom of the screen cover and eliminated the air gap.  Total reflectivity on the Dell is around 0.5%, from just the top surface.  This produces outstanding outdoor readability.

 

Here's how to quantify the outdoor readability.  A rule-of-thumb formula for the effective contrast ratio of an LCD used outdoors is as follows:

 

        Effective Contrast Ratio = 1 + (Emitted_Light / Reflected_Light)

 

Moderate sunlight is equivalent to about 10,000 nits.  If the screen reflects 0.5% of the sunlight, that's 50 nits of reflected light.  The Dell notebook LCD emits 500 nits, so the effective contrast ratio is 1 + (500 / 50) = 11:1.  This is very good.  For comparison, the effective contrast ratio of the New York Times newspaper in sunlight is around 20:1, which is about as good as it gets.  Here is a table of effective contrast ratio values:

 

 

Doing the same calculation for the Fujitsu T4215 with an Indoor/Outdoor Type #1 screen (with 1.5% reflectivity and ~200 nits of emitted light) yields the following:

 

        Effective Contrast Ratio = 1 + (200 / 150) = 2.3:1 = barely readable in the shade

You can see that there's no comparison.  What Dell has done is to combine both of the generally available methods of making a notebook screen readable outdoors (choices (a) and (b) from the introduction above).  They increased the screen brightness AND did an optimum treatment of the screen to reduce reflections.  If you look for an explanation of this on the Dell website, you won't find one because to some degree they regard it as their "secret sauce".  All they say on the website is that the screen has "a special non-reflective coating". 

 

Actually there's no secret.  Display and computer manufacturers have been doing optical bonding for a number of years; it's just that it has been limited mostly to specialized markets such as marine navigation displays.  Dell is the first commercial notebook manufacturer to apply it to notebooks.  Motion Computing has been applying it to slate-format Tablet PCs for several years, but a slate is still basically a specialized product.  Fujitsu hasn't done it so far because it costs a fair amount of money, and they don't want to increase the price of their notebooks and Tablets.  But I predict that Fujitsu will soon be forced to do it to remain competitive.

 

HP

 

In the next few months, HP will start shipping the Model 2710p, a new Tablet PC with an "optional Enhanced Outdoor-Viewable Display [that] offers more control in bright sunlight with no loss of battery life".  If you translate HP's marketing-speak, what they've done is to optically bond the screen cover to the LCD to create a single reflecting surface like on the Dell, but they have NOT increased the screen brightness above the typical 200 nits (thus "no loss of battery life"). Unfortunately, they also haven't applied an AR coating to the top surface of the screen cover, which leaves it at the standard 4% reflectivity of plain glass.  (The rumored reason is that HP believes "AR shows fingerprints too much"; one has to ask, which is worse -- fingerprints or an outdoor-viewable option that doesn't really work?)  Doing the same calculation for effective contrast ratio on the HP 2710p yields the following:

 

        Effective Contrast Ratio = 1 + (200 / 400) = 1.5 = barely readable in the shade

 

Even with the optical bonding, this is actually worse than the Fujitsu and much worse than the Dell.  The 2710p appears to be the only model on which HP is offering the "Outdoor View" option.  I suspect that the limited availability may be because HP is not yet confident that (a) this option will provide sufficient value to buyers, and/or (b) they can deliver it consistently at good margin (i.e., ensure a solid supply chain).

 

One difference between the Dell and the HP outdoor-readable notebooks is that HP is using "Illumi-Lite":

 

        "[The]12.1-inch diagonal widescreen Illumi-Lite display provides for a lighter and more

        energy-efficient notebook, providing improved battery life, compared to past generation

        Tablet PCs.  The chemically-strengthened glass top provides improved durability and a

        superior writing experience. An optional outdoor display panel improves viewability in

        sunlight, providing more contrast and less reflections."  (From the HP 2710p Overview Page)

 

Again translating HP's marketing-speak, Illumi-Lite is an LED (light-emitting diode) backlight.  This is the latest innovation in notebook displays, replacing the traditional CCFL (cold cathode fluorescent lamp) backlight.  An LED backlight makes the display thinner and lighter, uses less power, provides a better color gamut (range of colors), and can produce slightly more brightness, depending on how it's designed. 

 

Why isn't HP marketing these clear advantages more strongly?  I think it's just because they're being conservative.  LED backlights in notebooks are brand new, and HP isn't 100% confident in them yet.  This is their first product to use this new technology, and I think they don't want to over-hype it until they're more confident in both the technology and its supply chain.  I also think that they don't want to use the term "LED backlight" in their marketing because outside of geeks like me, very few people know what that means.  Instead, they make up a semi-redundant new brand-name ("Illumi-Lite") which actually has the same effect, since nobody knows what it means either!  If you search the entire HP website for "Illumi-Lite", eventually you'll find the following:

 

        "The Illumi-Lite displays used by our ultra-light business notebook PCs are thinner, lighter,

        and more energy-efficient, providing up to 90 minutes of additional runtime when compared

        to standard display technology."  (From an HP page entitled "Design and Engineering")

 

HP never actually defines what Illumi-Lite is.  Unfortunately, the marketing of technical products to consumers is getting to the point where it obscures practically all the useful technical information about a product, which I think is really unfortunate.

 

Panasonic

 

Panasonic has offered rugged and semi-rugged notebooks with outdoor-readable screens for a number of years.  Their current three products in this category are the Toughbook 19, the Toughbook 30 and the Toughbook 74.  The brightness specifications on these products point out an interesting issue, as follows:

 

 

Adding a touchscreen to a mobile computer makes the outdoor-readability problem significantly worse.  This is because a resistive touchscreen has four reflecting surfaces instead of just two as in the case of a simple screen cover.  An untreated touchscreen can reflect up to 20% of the incident light, which is almost impossible to compensate for.  Even with AR coating on all four touchscreen surfaces and on the LCD top surface, the best that can be achieved is about 4% total reflectivity.  To compensate for the higher reflectivity of a touchscreen, Panasonic doubles the brightness of their Toughbook 30 rugged notebook from 500 nits to 1,000 nits.  Applying the rule-of-thumb formula for effective contrast ratio yields the following:

 

        Effective Contrast Ratio = 1 + (1,000 / 400) = 3.5:1 = adequately readable in the shade.

 

The downside is that the 13.3" Toughbook 30 has a 90 watt-hour battery, and the product weighs 8.4 pounds. 

 

The Toughbook 19 and 74, on the other hand, are intended to be much more mobile.  Because of this, Panasonic can't increase the brightness (and resulting power consumption) to compensate for the higher reflectivity of a touchscreen.  Instead, the brightness with a touchscreen is 15% lower than the brightness without a touchscreen; this reduction is due to the light loss caused by the multiple layers in the touchscreen.  The result is that the Toughbook 19 and 74 are not as good performers outdoors, as shown by the results of the rule-of-thumb formula for the average of the Toughbook 19 & 74 with a touchscreen, as follows:

 

        Effective Contrast Ratio = 1 + (465 / 400) = 2.2:1 = barely readable in the shade.

 

The upside is that the battery in the 10.4" Toughbook 19 is only 61 watt-hours and the product weighs only 5.0 pounds.  On the other hand, the battery in the 13.3" Toughbook 74 is 87 watt-hours and the product weighs 6.0 pounds.  Everything's a tradeoff in mobile computer design, where there's no such thing as a free lunch.

Toshiba

 

Toshiba doesn't explicitly offer an outdoor-readable display on any of their notebooks or Tablet PCs.  However, the Portege R400 is marketed as having an "LED Backlight Display with High Brightness".  Unfortunately, the brightness level is not specified, so it's unclear what that actually means.  (Once again, marketing that obscures or omits significant technical details about the product!).  At least Toshiba doesn't try to mask the fact that they're using an LED backlight by inventing a meaningless brand-name for the technology. 

 

The LCD in the Portege R400 is a 12.1" WXGA (1280x800) transmissive TFT with "wide viewing angle".  How wide?  Who knows -- it's not specified!  This could be a BOE-Hydis 180-degree true wide-angle LCD, or it could be a standard Toshiba Tablet PC LCD with additional compensation films to extend the viewing angle from the normal 90 degrees to 120 or 130 degrees.  In either case, neither LCD manufacturer makes a Tablet PC LCD that's brighter than 250 nits.  Since there is no mention of anti-reflection coating in the detailed specifications, let's assume that it's a completely untreated screen.  This means 4% reflectivity from each of the front and back surfaces of the screen cover, and 2% from the LCD, for a total of 10% reflectivity (1,000 nits from the 10,000-nit sunlight).  Applying the rule-of-thumb formula yields the following:

 

        Effective Contrast Ratio = 1 + (250 / 1000) = 1.3:1 = totally unreadable outdoors

 

Even if the brightness were 500 nits, the effective contrast ratio would still only be 1.5:1, which is still essentially unusable.  The conclusion is that "High Brightness" in the case of the Portege R400 does NOT mean that the product is usable outdoors.  It just means that it's nice and bright indoors.

 

The Bottom Line

 

If you were to select a notebook from one of the above five manufacturers purely on the basis of outdoor readability, the decision would be fairly straightforward, with Dell winning by a landslide:

 

 

But in the real world, there are many additional selection criteria that must be considered.  The fundamental choices that tend to drive which notebook someone buys include the following: