In many displays there is a thin layer of air between the cover glass and the LCD. In optical bonding that layer is filled with adhesive. It sounds like a manufacturing detail, yet it changes three things that matter outdoors: how much ambient light the display throws back, whether it fogs up from the inside in the cold, and how well the glass layers survive a knock. This article explains the structure, describes the limits and shows which Getac devices in the RobustBook range have a LumiBond display according to their datasheets. Brightness in nits, anti-reflective treatment and polarizing filters are covered in the article on sunlight-readable displays. This one is only about the bonding.
A touch display consists of a cover glass, a touch sensor and the display itself. In the simple design the cover glass rests on a narrow frame or adhesive spot at the edge, and the middle is left as air. The display maker Beetronics describes this design as inexpensive, easy to manufacture and easy to repair, and as the most common method in consumer devices. In optical bonding a transparent adhesive fills the entire space between the LCD and the cover layer. The trade journal Information Display of the Society for Information Display defines the process as joining optical components with a clear adhesive whose refractive index is matched.
Getac calls its version LumiBond. In its description of LumiBond 2.0 the manufacturer writes that the touchscreen and the LCD are optically bonded with a clear resin and act functionally like a single layer of glass. The RobustBook datasheets give only the name LumiBond and not the term optical bonding. That it is a bonded stack is therefore documented by Getac's own description. Which LumiBond generation a given device carries is not stated in the datasheets.
There are two forms of adhesive. OCA (Optically Clear Adhesive) is a pre-formed adhesive film that is aligned and pressed between the layers. OCR (Optically Clear Resin) is a liquid resin that is dispensed between the layers and cured with UV light or heat. Some manufacturers write LOCA for Liquid Optically Clear Adhesive. According to Beetronics, OCA suits high volumes and standard sizes. OCR suits large or irregularly shaped displays but requires tight process control against shrinkage and overflow. Information Display names acrylic and silicone as the two most common materials for adhesive films.
What such an adhesive looks like is shown by the datasheet of the liquid adhesive LOCTITE AD 8650 from Henkel. The silicone is intended for gap filling in displays and cures under UV light. It has a refractive index of 1.41 and transmits more than 99% of the light at 550 nm through a layer 300 µm thick. During curing it shrinks by less than 1% of its volume, and after 1000 hours at 85 °C and 85% relative humidity it showed no delamination. Henkel gives these values for reference and not as a specification.
Light is partly reflected at every boundary between two materials with different refractive indices. For glass (index 1.5 to 1.52) against air, Information Display gives a reflectance of about 4.0 to 4.25% per interface. A stack with an air gap has three such surfaces: the top of the cover glass, its underside and the surface of the display. With untreated glass this adds up to about 12%. An anti-reflective cover glass lowers the total to 8.2%, because only the top surface improves. With bonding the two inner surfaces almost disappear, since adhesive and glass have similar refractive indices. What remains is 4% for plain glass and 0.2% for anti-reflective glass.
The authors work this into an example for a display in ambient light of 2000 foot-candles. The contrast ratio is 1.45 with anti-reflective glass without bonding and 18.37 with bonding. Without bonding, the display would have to emit 2969 foot-lamberts instead of 75 foot-lamberts by their calculation to reach the same contrast. That is a worked example for one particular display, not a measured value for a device in the range.
For LumiBond 2.0 Getac states that 0.2% of the light is lost to reflections, against 13.5% on average for consumer touchscreens. This refers to the share of the light the display generates itself. That is a different quantity from the reflectance for ambient light above, and the figures cannot be converted into each other. Getac also notes on the page that technical descriptions are simplified and approximated. We have no independent measurement.
The top glass surface keeps reflecting after bonding. Information Display therefore describes an anti-reflective treatment on the cover glass as the usual addition. Bonding does not replace it.
An air gap traps air together with its moisture. Information Display writes that such designs trap humidity between the cover glass and the display, which can impair legibility at low temperatures through vapor and ice. The display provider Data Modul attributes fogging to moisture that enters during strong temperature swings. Bonding fills the space where it would condense. Beetronics puts it this way: there is no room left for dust or condensation.
On LumiBond 2.0 Getac writes that removing the air gap reduces screen condensation in the cold, and it cites operation down to -30 °C. The datasheets of the devices in the table below give -29 °C to 63 °C as the operating temperature. The bonding affects only the space between the layers. The outer side of the glass is untouched by it.
Information Display rates the impact and shock resistance of a bonded display as much higher than that of a stack with an air gap. The adhesive layer absorbs part of the shock, and the cover glass and the front plate of the display are mechanically stronger together than apart. Impact resistance rises with the strength and thickness of the cover glass. If the glass does break, the adhesive holds the fragments together. Data Modul writes that the fixed connection between display and touch unit reduces sensitivity to mechanical impact. Getac describes LumiBond 2.0 as two thin layers of glass fused into a thicker one.
The manufacturer sources we retrieved give no test value, however, that separates the effect of the bonding from that of the housing. How far a device may fall follows from the whole construction and not from the bonding alone.
The biggest drawback is repair. Beetronics writes that repairs on bonded displays are so difficult that they are generally considered commercially unfeasible. The cover glass can therefore usually not be replaced on its own. If you want to repair displays in-house, clarify before buying whether the spare part is only the glass or the whole display unit.
On weight, the sources we retrieved give no figure. The datasheets of the Getac devices state the weight per device and not per display version. On the S510 the bonded display is an option, yet the datasheet lists only one weight of 2.35 kg. A weight comparison between bonded and non-bonded cannot be derived from that.
According to Beetronics, bonding is more complex and more costly than an air gap or adhesive tape. For liquid adhesives Information Display lists as weaknesses the cumbersome preparation of the material, shrinkage during curing and the risk of trapped air. This article gives no prices. For your selection that means: ask whether the bonded display is standard or an option. Bonding changes raw brightness only slightly. Information Display speaks of a moderate increase in luminance because less light is reflected back inside the stack. What the nits figure and transflective approaches mean is explained in the article Sunlight readable displays.
Fourteen Getac datasheets in the range contain a LumiBond entry. The table shows six of them with the core data from the respective datasheet. The other eight belong to the Ex variants UX10-EX, F110-EX, K120-EX and T800 EX ATEX, to the X600 and X600 Server, and to the G140 and F120. In the datasheets of the brands Durabook, Fieldbook, RuggON and Archos there is neither LumiBond nor any other statement about bonding. That does not mean their displays have an air gap, only that the datasheets are silent on it.
| Device | Display | Brightness (nits) | LumiBond entry in the datasheet | Operating temperature |
|---|---|---|---|---|
| Getac UX10 | 10.1 inches, WUXGA (1920 x 1200) | 1000 | LumiBond technology, capacitive multi-touch screen, optional dual mode | -29 °C to 63 °C |
| Getac F110 G7 | 11.6 inches, Full HD (1920 x 1080) | 1200 | LumiBond technology, usable in rain or with gloves | -29 °C to 63 °C |
| Getac K120 | 12.5 inches, Full HD (1920 x 1080) | 1200 | Full HD with LumiBond technology, usable with gloves, stylus or in rain | -29 °C to 63 °C |
| Getac A140 | 14 inches, 1366 x 768 (standard), optional Full HD (1920 x 1080) | 1000, 800 with the Full HD option | 14-inch screen with LumiBond technology | -29 °C to 63 °C |
| Getac V110 G7 | 11.6 inches, Full HD (1920 x 1080) | 1000 | capacitive LumiBond multi-touch | -29 °C to 63 °C |
| Getac S510 | 15.6 inches, Full HD (1920 x 1080) | 1000 (standard) | optional only: capacitive LumiBond multi-touch screen | -29 °C to 63 °C |
Two rows deserve a second look. On the S510 LumiBond appears only as an option in the datasheet, and the datasheet names a touchscreen as the standard and lists LumiBond separately as an option. On the A140 the datasheet names the technology for the 14-inch screen as a whole and lists two resolutions with different brightness. For both devices, have the configuration confirmed explicitly in the quote.
LumiBond is Getac's name for its bonded display. Getac describes LumiBond 2.0 as an optical connection of touchscreen and LCD with a clear resin. The datasheets in the range give only the name LumiBond.
Only slightly. Information Display names a moderate increase in luminance. The better readability outdoors comes mainly from less ambient light being reflected back.
As a rule, no. According to Beetronics, repairs on bonded displays are not commercially feasible. Clarify before buying what the spare part includes.
The datasheets of the F110 G7 and K120 name use in rain or with gloves together with LumiBond. Getac attributes the adjustment of touch sensitivity in the presence of water to LumiBond 2.0. More on this question is in the article Touch in wet conditions and with gloves.
If you use a tablet or laptop mostly outdoors, work in frost or changing temperatures, or expose the device to knocks in vehicles and on building sites, put a device with a bonded display on your shortlist. The six Getac devices in the table list LumiBond in their datasheets, on the S510 only as an option. Bonding makes less sense for a device that runs almost only indoors. Anyone who wants to replace displays themselves is also worse served by it. For that case none of the devices named here is suitable.
You can find more devices for outdoor use under outdoor tablets. If you have questions about the configuration and the options, the RobustBook team is happy to help you choose.