The viewing angle of an LCD panel is generally expressed for both horizontal and vertical in degrees from perpendicular to the display or as a total of left & right and up & down. So for example the newer IPS panels now claim up to 178 degree viewing angle.
A few important points to note with viewing angle:
- As I am likely to mention for other specifications it is difficult to choose a panel solely on specification, it is worth seeing the panel. I have seen a panel with excellent viewing angle ratings but when testing it I found a color shift at around 45 degrees from perpendicular.
- Specifications are generally expressed for the panel in landscape orientation so if the panel is going to be used in portrait mode the up/down viewing angle in the specification will be very relevant.
- TN type TFT panels may only offer a viewing angle of 130 degrees with different up/down results making them unsuitable for portrait mode.
Overall viewing angle is becoming less of an issue as there are panel choices to meet the requirements of most users.
In the commercial and professional market display systems differ in many significant respects and are far from the commoditization of the consumer monitor market. The differences are both external and internal:
- Panel choice: Brightness and temperature range are two obvious and significant factors as well as color, resolution, viewing angle and even shape.
- Enclosure design: Size, shape, ruggedness and controls.
- User interface: Very likely to be quite different with presets for specific functions, different type of controls such as a joystick or remote activation.
- Signal inputs: Aside from standards such as HD-SDI there are many custom signal requirements.
- Power supply: Especially in transport and industrial equipment display systems are likely to have different power supply requirements.
- Environmental: Resilience against dust, humidity and other that require conformal coated electronics.
- Compliance: A major factor can be the specific compliance requirements for a market application such as for medical or commercial marine.
- Lifetime & Lifecycle: Not just operating lifetime but also the production lifecycle of the components – we often have to supply the same LCD controller for over 5 years.
The above are just some headline differences but provide a clear indication how many permutations of display system design there can be to meet different niche market requirements. It is an exciting market with considerable scope for creativity and innovation.
The Hong Kong Heritage Museum kindly sent over some photos of recent installations using Digital View VideoStream media players and VideoFlyers.
The Digital View LCD Controller summary on the website has been completely revised and a downloadable version also made available. This summary makes comparison more straightforward than the previous presentation.
Each of the items on the website summary are linked to more detailed pages for each product.
The Digital View LCD controller page has been completely rewritten with a new summary together with a version for download. This can be seen here.
Digital View LCD Controller Summary
LCD panel brightness is normally expressed in terms of Nits or Candelas/meter2 (cd/m2), they are equivalent, and refers to the manufacturers measurement under the following conditions:
- After the backlight has had time to warm up to reach full potential,
- From directly in front of the middle of the panel,
- With transmissivity at maximum, so if the panel is normally white then probably with no input signal or if the panel is normally black then with a full white signal.
There are no standards for suitable brightness levels for various applications which is reasonable considering other factors will affect the outcome but as a general guideline it would seem that the following ranges apply:
- Notebook type computers: Around 200~250 Nits
- Desktop monitors: Typically up to 450 Nits
- TV’s and video displays: 400~600 Nits
- Public displays: Generally around 600~700 Nits
- Outdoor displays: 700~1,500 Nits.
Other factors: Contrast – as I was being told this morning a 700 Nit panel with excellent contrast proved to be considerably better in an outdoor application than a 1,500 Nit panel with lower contrast.
The bottom line is that it is very difficult to make a decision based on the specifications and the display needs to be evaluated in its environment.
Some applications require low light visibility which is another topic.
HDMI is a consumer products video interface specification as set by the HDMI organization (www.hdmi.org). The organization was founded by consumer products companies to both simplify the inter-connection of consumer media devices as well as protecting the interests of content developers (by using encryption, HDCP, and other restrictions).
From 1 January 2012 HDMI was no longer referred to with version numbers, instead the reference will be HDMI Standard, HDMI Standard with Ethernet and so on.
Due to the growing popularity of HDMI many non-consumer products have also incorporated HDMI support – as a note one of the most frequently mentioned drawbacks in this context is the lack of any locking mechanism in the connector design.
The digital alternatives: 3G-SDI/HD-SDI, DVI, DisplayPort, HD-BaseT.
Daniel Howe and Bill Seaman have put together a very impressive installation comprising 16 LCD panels in the Hong Kong City University, Run Run Shaw Creative Media Centre. This is on exhibit now until the end of April 2012.
Engine of Engines, a reactive multimedia installation by Daniel Howe & Bill Seaman ©2011
Common to most LCD panels used in display systems is that they are Thin Film Transistor (TFT) ‘active matrix’ type, each pixel has its own thin film transistor which acts as the switch.
So what are TN, IPS and MVA panels? This refers to the crystal structure, they are still active matrix.
- TN (Twisted Nematic): This is the most common panel and used in everything from laptops to TV’s.
- IPS (In Plane Switching): Originally developed by Hitachi IPS panels it use a different crystal structure to improve the viewing angle and other characteristics. The iPad was launched with an IPS panel.
- MVA (Multi-domain Vertical Alignment): Used by some panel manufacturers as competitive to IPS panels in terms of viewing angles, color and response times.
Viewing angles on LCD panels are now rated at up to 178 degrees with 160 degrees being common. Whether these are meaningful numbers may depend on the application and user perception but the point is that viewing angle does not appear to be a barrier to developing a display system.
Note: There are alternative technologies such as PVA, ASV and PLS but for now TN, IPS and MVA are the most common.
As SID explain it:
At Display Week 2012, the Society for Information Display is providing a new forum for live demonstrations of emerging information display technologies and related areas. This new exhibit platform is called the “Innovation Zone” (I-Zone) and will appear in the main Exhibit Hall, under the sponsorship of E Ink Holdings, on June 5-6 in the Boston Convention and Exhibition Center in Boston, Massachusetts.
They will also select a winner for “Best Prototype at Display Week”.
Further details can be found at http://www.sid.org/IndustryNews/tabid/300/EntryId/30/SID-Debuts-Innovation-Zone-for-Cutting-Edge-Display-Technologies.aspx
The Digital View website has frequent mention of ‘multi-panel’ support, maybe more accurately expressed as multi-panel timing support.
What is multi-panel support?
Different LCD panel models have different signal timing requirements – Digital View LCD controllers are referred to as multi-panel because they have these timings stored on-board and selectable by mini-dip switches.
The mini-dip switch settings can be found on the Connection Diagrams available for download from the Digital View CSG mentioned in an earlier post or by contacting Digital View directly.
When choosing an LCD panel, size and resolution are probably the two characteristics that are at the top of everyone’s list – but for a display system that matches the needs of the target market there are many other specs to consider; in no particular order:
- Brightness – high up on many people’s list
- Viewing angle
- Response time
- Refresh rate
- Temperature range
- Backlight type & specification
- Production life-cycle
- Power consumption
- Color characteristics
- Surface finish
- AQL re pixels
And more – to be continued…
LEDs operate from DC and are relatively easy to work with but there are three points that help understand regarding the role of an LED driver:
- Voltage: LEDs in a backlight will be wired in series so in each LED requires 3v and there are 20 LEDs the voltage required will be 60v.
- Current: The driver will maintain a constant current to the LED’s.
- Brightness control: Two normal methods to control brightness are by varying the current or using a technique called Pulse Width Modulation (PWM*).
For a display system design perspective the complex work is done by the LED driver design and usage is as straightforward as following the connection specifications.
* PWM creates the impression of lower light by switching the LEDs on/off but at a frequency faster than our perception. Using PWM the brightness can be lower than achievable by simply reducing the current.
As shown in the Corning video ‘A Day Made of Glass’ (mentioned in an earlier blog) and movies like Avatar and Minority Report, transparent displays look exciting.
Attendees of certain trade shows will know that transparent LCD displays have been around for a while but it is only relatively recently that they have been available for use in real applications. The transparency is not as in the movies, it is more like 15~20%, but nevertheless it is considered adequate for some applications.
Typical applications right now seem to be retail promotion related but it will be interesting to see where innovation takes this.
Here is a link to Samsung’s recent press release announcing their 46” transparent display: http://www.samsung.com/us/business/semiconductor/newsView.do?news_id=1256
Photo: Taken at a trade show in 2011
The inside of a normal LCD monitor or TV is pretty straightforward as this diagram shows: