Dec. 04, 2023
Electronic Components & Supplies
It seems as if modern displays have all kinds of different labels: high definition, 3D, smart, 4K , 4K Ultra, the list goes on. The two most common labels are LCD and LED. What’s the difference between the two? Is there a difference? And does this difference make one or the other preferable for certain types of activities like gaming or graphic design?
All LED monitors are LCD monitors. But not all LCD monitors are LEDs. Kind of like all eagles are birds, but not all birds are eagles. While the names might be confusing to those wading through specs to find the best monitor, once you break it down it’s easier to understand than you think.
We’ll explain the tech and the naming conventions, and then highlight some HP monitors that might be the perfect fit for your needs. Let’s figure out exactly what LCD and LED monitors are and how to pick the right one for you.
Both types of displays use liquid crystals to help create an image. The difference is in the backlights. While a standard LCD monitor uses fluorescent backlights, an LED monitor uses light-emitting diodes for backlights. LED monitors usually have superior picture quality, but they come in varying backlight configurations. And some backlight configurations create better images than others.
Until 2014, plasma displays were the most commonly manufactured displays. But then the LCD took over. LCD stands for liquid crystal display. We’ll go over what that means in a minute. But first, it’s important to note that an LED also uses liquid crystals, so the name is somewhat misleading. Technically, an “LED monitor” should really go by the name, “LED LCD monitor.”
First, let’s go over how LCD and LED monitors utilize liquid crystals. The science behind this stuff features an incredibly complicated mix of optics, electrical engineering, and chemistry. But we’ll explain it in layman’s terms.
The key term here is “liquid crystal.” In high school, you might have been taught that there are three states of matter: solids, liquids, and gases. But there are some substances that are actually a strange blend of different states. A liquid crystal is a substance that has properties of both a solid and a liquid. When you get to the upper tiers of science, you begin to discover that everything you once knew is wrong.
Solid properties: The molecules in the liquid crystal can form a simple, highly geometric shape
Liquid properties: The molecules in the liquid crystal can also have a fluid, unstructured shape
Typically, the molecules in a liquid crystal are bunched up in a very dense and unstructured arrangement. But when the liquid crystal is exposed to electricity, the molecules suddenly expand into a very structured, interconnected shape [1].
Pixels are the basic building blocks of a digital image. A pixel is a small dot that can emit colored light. Your display is composed of thousands of pixels, and they’re in a variety of different colors to give you your computer interface and the webpage that you’re currently reading. It works like a mosaic, but each individual piece is much less noticeable.
Every pixel is composed of three color filters, which are called “subpixels.” There’s a red, blue, and green subpixel for every pixel [1].
Every pixel is composed of two glass sheets, and the outermost sheet has the subpixels. The liquid crystals are sandwiched between the two sheets.
LCD monitors have backlights behind the screen that emit white light, and the light can’t pass through the liquid crystals while they’re in their liquid arrangement. But when the pixel is in use, the monitor applies an electric current to the liquid crystals, which then straighten out and allow light to pass through them [2].
Every pixel has three separate backlights which can shine through the red, blue, or green color filter – that’s how a pixel can emit a specific color.
Here’s how an LCD is structured from the back (furthest from you) to the front (closest to you):
Backlights
Sheet #1
Liquid Crystal
Sheet #2, with color filters
Screen
While both LCD and LED monitors make use of liquid crystals, it’s the backlighting that really makes them different from one another [2].
Standard LCD monitors employ “cold cathode fluorescent lamps,” also known as CCFLs as backlights. These fluorescent lights are evenly placed behind the screen so that they deliver consistent lighting across the display. All regions of the picture will have similar brightness levels.
LED monitors don’t use fluorescent lamps. Instead, they use “light-emitting diodes,” which are extremely small lights. There are two methods of LED backlighting: full-array backlighting and edge lighting.
Full-array backlighting
With full-array backlighting, the LEDs are placed evenly across the entire screen, similar to an LCD setup. But what’s different is that the LEDs are arranged in zones. Each zone of LED lights can be dimmed (also known as local dimming).
Local dimming is a very important feature that can dramatically improve picture quality. The best images are ones that have a high contrast ratio; in other words, images that have both very bright pixels and very dark pixels simultaneously.
When there’s an area of the picture that needs to be darker (a night sky, for instance), the LEDs in that region of the picture can be dimmed to create a truer black. This is not possible on standard LCD monitors, where the entire picture is lit evenly throughout.
With local dimming, the monitor can create more precise illumination, which results in greater picture quality.
Edge lighting
Some LED monitors have edge lighting. This is where LEDs are placed along the edge of the screen rather than behind it. The LEDs can be placed:
Along the bottom of the screen
Along the top and bottom of the screen
Along the left and ride sides of the screen
Along all four sides of the screen
There are no local dimming capabilities in edge-lighted displays, so they can’t create pictures that are as high-quality as those created by full-array LEDs. However, edge lighting enables manufacturers to create extremely thin displays that don’t cost as much to produce - and which are better for a tight budget.
When it comes to picture quality, full-array LED monitors are almost always superior to LCD monitors. But bear in mind that only full-array LEDs are superior. Edge-lit LEDs may actually be inferior to LCD monitors.
A full-array LED monitor should be your number one choice for gaming. Steer clear of its edge lighting. The problem with edge lighting is that you’ll have fewer optimal viewing angles with which to play games. That’s not an issue if you prefer to sit directly in front of the screen while you’re gaming. But if you like to kick back in your chair or view from different angles, you’ll find that an edge-lit LED loses visibility as you move away from the center viewing angle.
But even if you play while you’re directly in front of the monitor, edge-lit LEDs have more issues with glare than full-array LEDs do. That’s because of the uneven lighting (very bright around the edges, darker as you approach the center of the display). Because the pixels are evenly lit, LCD monitors tend to have better viewing angles and anti-glare than edge-lit LEDs.
Edge-lit LEDs do have two big advantages. If you have a very tight space in which to fit your monitor, you’ll like having an edge-lit LED because they’re usually thinner than the other types. They’re also less expensive to manufacture, which make them easier on the wallet.
When you’re shopping for a new display, don’t forget to review all of its specs. While the backlighting type is important, you should also take the resolution and refresh rate into account.
Resolution refers to how many pixels are displayed on the monitor. Remember, the more pixels you have, the more dynamic your composition of colors can be. The highest-quality monitors have resolutions of at least 1920x1080.
Refresh rate refers to how quickly your monitor updates the display with new information from your computer’s GPU. If you’re a gamer, it’s important that you get a monitor with a very fast refresh rate (30 Hz to 60 Hz) so you won’t suffer from screen tearing - a nasty visual effect that happens when your monitor can’t keep pace with the GPU.
Because LED monitors create better pictures than LCD monitors, nearly all of HP’s displays are built with LED backlights. When you’re browsing through the HP LED monitors, you might notice that some of them are equipped with either “IPS” or “AHVA” technology. These refer to the types of liquid crystal panels that are used. Both are fantastic, although they have some minor differences:
IPS: Better color production and viewing angles
AHVA: Better refresh rates and contrast ratios
Still, many consumers believe that there is little to no discernible difference between the two [3].
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You’ll also see that some monitors have “TN” LED backlights. This is the oldest form of liquid crystal technology. It’s still very effective, but TN panels are typically used in small, work-oriented monitors that are made to be mounted or used in the field.
These top-of-the-line HP LED monitors are among the best of the best. Give them a quick look if you’re in the market for a new display.
For the gamer
For the digital artist
If you’re a digital illustrator, video editor, photo editor, or special effects wiz, you should give the HP EliteDisplay S270n 27-inch 4K micro-edge monitor a look. When you’re creating digital art, you need the most expansive resolution and highest-quality color production possible, and that’s what you’ll get with this IPS-equipped monitor. The micro edge screen makes it easy to use dual monitors , but the 27-inch screen alone gives you a wide interface to work on.
For the working professional
If you’re a business person, try one our HP EliteDisplay monitors , like the HP EliteDisplay E243 23.8-inch monitor . The IPS LED display is gorgeous and will give you a crisp and clear picture no matter what software you’re using. The micro edges make it perfect for a dual monitor setup, and the 23.8-inch size is wide, but not too large to accommodate a second monitor or to fit into tighter workstations.
There are some up-and-coming technologies that are making LED displays even better. OLED and QLED displays are bound to become more commonplace in the future.
“OLED” stands for “organic light-emitting diode.” What makes an OLED unique is that each pixel has a light source that can be individually shut off. On an LED monitor, the only way to keep a pixel from emitting light is to keep the liquid crystal closed. It’s effective, but not perfect - a small portion of light will always seep through. On an OLED monitor, each pixel’s light can be entirely shut off, so no light at all will emanate through the liquid crystal. These means you can get truer blacks, which means deeper contrast ratios and better image quality.
There are two additional advantages. First, OLED monitors can be made even thinner than LED monitors because there’s not a separate layer of LEDs behind the pixels. Second, these monitors are more energy efficient because the pixels will only draw power when their light is turned on. One of the downsides, though, is that pixel burn-in will be more noticeable since some pixels will inevitably be used more than others [4].
“QLED” stands for “quantum light-emitting diode.” In a QLED monitor, each pixel has a “quantum dot.” Quantum dots are tiny phosphor particles that glow when you shine a light upon them [5].
Why would you need a glowing particle over each pixel? Because LEDs aren’t very good at emitting bright light. The brightest color is white. But an LED doesn’t emit white light – it emits blue light. Each LED is given a yellow phosphor coating to make it appear less blue and more white, but it’s still not true white. The “blueness” of LEDs negatively impacts the red, blue, and green colors on LED displays. LED monitors have automatic features that adjust the RGB colors to compensate for the blue light, but it can’t compensate for the weaker light intensity.
That’s where the quantum dots come in. The pixels are overlayed by a sheet of red and green quantum dots (there is no blue because blue light is already being emitted by the LED). When the light shines through the liquid crystals, the quantum dots glow, and you’re given a bright, vivid, and lovely spectrum of RGB colors.
QLED monitors are capable of creating pictures that are both dynamic and bright, and which have stellar contrast ratios.
Displays are a complicated science, right? But next time you’re shopping for monitors at the store or on our HP Store site, you’ll be a true expert and will be able to pick out exactly the right display for you.
Zach Cabading is a contributing writer for HP® Tech Takes. Zach is a content creation specialist based in Southern California, and creates a variety of content for the tech industry.
The use of liquid crystal displays (LCDs) in user interface assemblies is widespread across nearly all industries, locations, and operating environments. Over the last 20 years, the cost of LCD displays has significantly dropped, allowing for this technology to be incorporated into many of the everyday devices we rely on.
The odds are high you are reading this blog post on a laptop or tablet, and it’s likely the actual screen uses LCD technology to render the image onto a low-profile pane of glass. Reach into your pocket. Yes, that smartphone likely uses LCD technology for the screen. As you enter your car, does your dashboard come alive with a complex user interface? What about the menu at your favorite local drive-thru restaurant? These are some everyday examples of the widespread use of LCD technology.
But did you know that the U.S. military is using LCD displays to improve the ability of our warfighters to interact with their equipment? In hospitals around the world, lifesaving medical devices are monitored and controlled by an LCD touchscreen interface. Maritime GPS and navigation systems provide real-time location, heading, and speed information to captains while on the high seas. It’s clear that people’s lives depend on these devices operating in a range of environments.
As the use of LCDs continues to expand, and larger screen sizes become even less expensive, one inherent flaw of LCDs remains: LCD pixels behave poorly at low temperatures. For some applications, LCD displays will not operate whatsoever at low temperatures. This is important because for mil-aero applications, outdoor consumer products, automobiles, or anywhere the temperature is below freezing, the LCD crystal’s performance will begin to deteriorate. If the LCD display exhibits poor color viewing, sluggish resolution, or even worse, permanently damaged pixels, this will limit the ability to use LCD technologies in frigid environments. To address this, there are several design measures that can be explored to minimize the impact of low temperatures on LCDs.
Most LCD displays utilize pixels known as TFT (Thin-Film-Transistor) Color Liquid Crystals, which are the backbone to the billions of LCD screens in use today. Since the individual pixels utilize a fluid-like crystal material as the ambient temperature is reduced, this fluid will become more viscous compromising performance. For many LCD displays, temperatures below 0°C represent the point where performance degrades.
Most LCD displays utilize pixels known as TFT (Thin-Film-Transistor) Color Liquid Crystals, which are the backbone to the billions of LCD screens in use today. Since the individual pixels utilize a fluid-like crystal material as the ambient temperature is reduced, this fluid will become more viscous compromising performance. For many LCD displays, temperatures below 0°C represent the point where performance degrades.
Have you tried to use your smartphone while skiing or ice fishing? What about those of you living in the northern latitudes - have you accidently left your phone in your car overnight where the temperatures drop well below freezing? You may have noticed a sluggish screen response, poor contrast with certain colors, or even worse permanent damage to your screen. While this is normal, it’s certainly a nuisance. As a design engineer, the goal is to select an LCD technology that offers the best performance at the desired temperature range. If your LCD display is required to operate at temperatures below freezing, review the manufacturer’s data sheets for both the operating and storage temperature ranges. Listed below are two different off-the-shelf LCD displays, each with different temperature ratings. It should be noted that there are limited options for off-the-shelf displays with resilience to extreme low temperatures.
Item Symbol Condition Min. Max. Unit Operating Temperature Range TOP Absolute Max 0 +50 °C Storage Temperature Range TST Absolute Max -20 +60 °C
Item Symbol Condition Min. Max. Unit Operating Temperature Range TOP Absolute Max -20 +70 °C Storage Temperature Range TST Absolute Max -30 +80 °C
For many military applications, in order to comply with the various mil standards a product must be rated for -30°C operational temperature and -51°C storage temperature. The question remains: how can you operate an LCD display at -30°C if the product is only rated for -20°C operating temperature? The answer is to use a heat source to raise the display temperature to an acceptable range. If there is an adjacent motor or another device that generates heat, this alone may be enough to warm the display. If not, a dedicated low-profile heater is an excellent option to consider.
Made of an etched layer of steel and enveloped in an electrically insulating material, a flat flexible polyimide heater is an excellent option where space and power are limited. These devices behave as resistive heaters and can operate off a wide range of voltages all the way up to 120V. These heaters can also function with both AC and DC power sources. Their heat output is typically characterized by watts per unit area and must be sized to the product specifications. These heaters can also be affixed with a pressure sensitive adhesive on the rear, allowing them to be “glued” to any surface. The flying leads off the heater can be further customized to support any type of custom interconnect. A full-service manufacturing partner like Epec can help develop a custom solution for any LCD application that requires a custom low-profile heater.
Example of a Polyimide flexible heater.
With no thermal mass to dissipate the heat, polyimide heaters can reach temperatures in excess of 100°C in less than a few minutes of operation. Incorporating a heater by itself is not enough to manage the low temperature effects on an LCD display. What if the heater is improperly sized and damages the LCD display? What happens if the heater remains on too long and damages other components in your system? Just like the thermostat in your home, it’s important to incorporate a real-temp temperature sensing feedback loop to control the on/off function of the heater.
The first step is to select temperature sensors that can be affixed to the display while being small enough to fit within a restricted envelope. Thermistors, thermocouples, or RTDs are all options to consider since they represent relatively low-cost and high-reliability ways to measure the display’s surface temperature. These types of sensors also provide an electrical output that can be calibrated for the desired temperature range.
The next step is to determine the number of temperature sensors and their approximate location on the display. It’s recommended that a minimum of two temperature sensors be used to control the heater. By using multiple sensors, this provides the circuit redundancy and allows for a weighted average of the temperature measurement to mitigate non-uniform heating. Depending on the temperature sensors location, and the thermal mass of the materials involved, the control loop can be optimized to properly control the on/off function of the heater.
Another important consideration when selecting a temperature sensor is how to mount the individual sensors onto the display. Most LCD displays are designed with a sheet metal backer that serves as an ideal surface to mount the temperature sensors. There are several types of thermally conductive epoxies that provide a robust and cost-effective way to affix the delicate items onto the display. Since there are several types of epoxies to choose from, it’s important to use a compound with the appropriate working life and cure time.
For example, if you are kitting 20 LCD displays and the working life of the thermal epoxy is 8 minutes, you may find yourself struggling to complete the project before the epoxy begins to harden.
Before building any type of prototype LCD heater assembly, it’s important to carefully study the heat transfer of the system. Heat will be generated by the flexible polyimide heater and then will transfer to the LCD display and other parts of the system. Although heat will radiate, convect, and be conducted away from the heater, the primary type of heat transfer will be through conduction. This is important because if your heater is touching a large heat sink (ex. aluminum chassis), this will impact the ability of the heater to warm your LCD display as heat will be drawn toward the heat sink.
Insulating materials, air gaps, or other means can be incorporated in the design to manage the way heat travels throughout your system on the way toward an eventual “steady state” condition. During development, prototypes can be built with numerous temperature sensors to map the heat transfer, allowing for the optimal placement of temperature sensors, an adequately sized heater, and a properly controlled feedback loop.
Before freezing the design (no pun intended) on any project that requires an LCD display to operate at low temperatures, it’s critical to perform low temperature first. This type of testing usually involves a thermal chamber, a way to operate the system, and a means to measure the temperature vs time. Most thermal chambers provide an access port or other means to snake wires into the chamber without compromising performance. This way, power can be supplied to the heater and display, while data can be captured from the temperature sensors.
The first objective of the low-temperature testing is to determine the actual effects of cold exposure on the LCD display itself. Does the LCD display function at cold? Are certain colors more impacted by the cold than others? How sluggish is the screen? Does the LCD display performance improve once the system is returned to ambient conditions? These are all significant and appropriate questions and nearly impossible to answer without actual testing.
Temperature vs. time graph: 5 channels monitored with chamber at -35 degrees Celsius.
As LCD displays continue to be a critical part of our society, their use will become even more widespread. Costs will continue to decrease with larger and larger screens being launched into production every year. This means there will be more applications that require their operation in extreme environments, including the low-temperature regions of the world. By incorporating design measures to mitigate the effects of cold on LCD displays, they can be used virtually anywhere. But this doesn’t come easy. Engineers must understand the design limitations and ways to address the overarching design challenges.
A full-service manufacturing partner like Epec offers a high-value solution to be able to design, develop, and manufacture systems that push the limits of off-the-shelf hardware like LCD displays. This fact helps lower the effective program cost and decreases the time to market for any high-risk development project.
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