9 LCDs Terms Every Engineer Should Know
Engineers choosing an LCD for their next product will encounter most of these terms and should be aware what each means, and how it may affect the price and design cycle of their project.
Minimum Order Quantity (MOQ) order quantity is the smallest production size order you can place with your LCD supplier.
Most standard, off-the-shelf displays have no or a very low MOQ.
Custom displays require a higher MOQ since the display is only being built for one customer. The manufacture must purchase a minimum lot size of raw materials such as ITO glass, PCBs, bezels etc. They cannot use the raw materials for any other display; therefore, the end customer must use all the raw materials.
MOQs does not apply to samples/prototypes of standard or custom LCDs.
Break down of MOQs per display technology:
Segment (Static) Displays:
Segment display MOQs can range from 500 to 5K units per order. The smaller the glass, the higher the MOQ.
Character LCDs and Monochrome Graphic LCDs:
Custom character displays MOQs are low and range from fifty units to a few hundred. Most standard character LCDs have no MOQ.
TFTs and OLED Displays:
If you need a fully custom TFT, then the MOQ can be as high as 10K to 50K.
Modified TFTs, such as a TFT with a custom backlight or added cable, have MOQs in the hundreds.
If you need a standard TFT, there is no or a very small MOQ.
Lead-time is the amount of time from when the LCD order is placed, and the product arrives at the customer’s location.
A contract manufacturer (CM) is a company that builds/assembles products for other companies. Many OEMs will design the product, but they do not have the resources to build it. Often times a CM can build the product for less money than the OEM can.
Most times, the CM purchases all the components and then assembles the product according to the OEMs instruction. The CM cannot choose who they purchase the LCDs from. They must purchase from the OEMs approved supplier.
Tooling, aka a Non-recurring engineering (NRE) charge, is the price of designing a custom LCD.
Reduction of Hazardous Substance (RoHS) has been the standard for many years. Most LCDs are built to meet RoHS requirements.
It is possible to build a display with the older (pre-RoHS) materials such as lead based solder, but this needs to be special ordered. Some industries such as aviation and military allow the use of non-RoHS materials.
A sunlight readable display is one that can be easily read in bright light. E book readers and the older digital watches are good examples of this.
Most color displays such as TFTs and OLEDs are not sunlight readable and their display washes out in the sun. Most monochrome displays are sunlight readable.
It is possible to reduce the wash out of display by adding films, using a different polarizer, or increasing the brightness of the display’s backlight. (increasing brightness is the most popular option, but draws more power and may not be the best choice for products meant to have low power consumption).
Nits is the measure of brightness of the LCD’s backlight.
One Nit is equal to the candela per square meter (cd/m 2). Many non-sunlight readable LCDs use a bright backlight to overpower the sun and make the display readable in direct sunlight. To do this, the backlight’s brightness must be a minimum of 700 Nits. Many designs use a 1K Nit backlight to compete with the sun.
The brighter the backlight, the more power needed and the higher power consumption is.
If power consumption is critical, think about using a monochrome LCD where the display is readable in sunlight.
Many displays contain a backlight to make the display readable in the dark. Most backlights are made with light-emitting diodes (LEDs).
Half-life is the amount of time it takes to reduce an LED to half its brightness.
If an LED has a rated half-life of 70K hours, the display will be half as bright after being on for 70K hours. It will then be half as bright again at 140K hours. This process will continue.
A factor that reduces an LED’s half-life is overdriving the LED with too much current to increase brightness and operating in excessive heat.
End of Life (EOL) is the dreaded phrase feared by most OEMs. It means that a component of their product will no longer be manufactured.
The OEM must find a new supplier for a drop-in replacement for this component before they run out of inventory of a component and their production line goes down.
When sourcing a new LCD, ask the supplier what the expected production lifetime of the display is. Make sure you are not purchasing surplus displays from a broker because once the stock is gone, then you are out of luck.
Monochrome displays have the least probability of obsolesce.