I. What is a monochrome display?
 
A monochrome display is a type of screen that can only show one colour and different levels of brightness. The most important idea is to control how much light is emitted from each pixel to create a range of shades from dark to bright using a single primary colour (most commonly green, amber, and red), rather than displaying a "pure colour without gradation".
 
From a technical perspective, early monochrome displays mostly used CRT (cathode ray tube) technology, which used an electron beam to bombard a monochromatic phosphor on a fluorescent screen to emit light, such as the classic green screen terminal. Modern monochrome displays mainly use technologies such as LCD and OLED, which limit the output of a single color through filters while retaining brightness adjustment functionality. Its core characteristic is: a single color dimension, but the brightness dimension can be adjusted in multiple gradients, not just displaying a pure binary image of "black and white."
 
Monochrome displays are used in many situations. They are good for situations where the colour is not important, but clarity and battery life are. They have some good points. They are simple, they do not use much power, they are very stable and they are cheap. Some examples of this are early computer terminals, the displays of cash registers, industrial control panels, some electronic dictionaries, and older calculators.
 
II. Which is better, a grayscale display or a monochrome display? 

To determine whether one is "better," the core factor depends on the usage scenario and needs—they are not absolutely superior or inferior, but rather differentiated choices based on different requirements. Let's first clarify the core attributes of grayscale displays, and then compare them from key dimensions:
 
1. The core definition of a grayscale display
 
A grayscale display is an "advanced form" of a monochrome display. Strictly speaking, all grayscale displays belong to monochrome displays, but not all monochrome displays possess rich grayscale performance. Its core advantage lies in achieving finer brightness gradients (i.e., "grayscale levels") on a single primary color basis, such as the common 16, 64, and 256 grayscale levels. This allows for more accurate representation of the light and dark levels in an image, approaching the display effect of a black and white photograph.
 
For example, in scenarios such as X-ray display in the medical field and image analysis in industrial inspection, it is necessary to distinguish details through differences in light and dark. In these cases, high grayscale monochrome displays become a necessity.
 
2. Core Dimension Comparison (with Selection Suggestions)
 

Comparison Dimensions	Monochrome display (low grayscale / no grayscale)	Grayscale display (high grayscale)	Selection Recommendation
Display effect	Only a single color, with few levels of light and dark (e.g., only two levels: "light" and "dark").	It uses a single color, but has a rich gradient of light and dark (up to 256 levels), with clear details.	To display image depth and detail, select a grayscale monitor; to display only text/simple symbols, select a monochrome monitor.
Technology costs	Simple structure, low price, and low power consumption	An additional grayscale control chip is needed, which increases the cost and slightly increases power consumption.	Limited budget, low power consumption: Choose a monochrome monitor; Ample budget, attention to detail: Choose a grayscale monitor.
Applicable Scenarios	Text terminal, calculator, simple industrial indicator lights, POS machine	Medical imaging (X-ray, ultrasound), industrial inspection, black and white monitoring, professional drawing preview	In scenarios requiring high detail, such as medical and testing applications, grayscale displays are preferred; for displaying basic information, monochrome displays are preferred.
Visual experience	Low visual impact, less eye strain during prolonged viewing (e.g., green screens)	It has strong detail, but the single color makes it visually monotonous.	Long-term text processing → monochrome display; image detail analysis → grayscale display

 
3. Summary: There is no "absolutely better," only "more suitable." 

If your needs are for basic information display (such as text, numbers, and simple icons), and you prioritize low cost, low power consumption, and stability, then a monochrome monitor is a better choice, as it can meet your core needs at the lowest cost.
 
If your needs are for detailed presentation (such as medical images and industrial inspection images), requiring the differentiation of image layers through differences in brightness and darkness, then a grayscale monitor is more suitable. Its high grayscale level can accurately reproduce details and avoid information loss.
 
III. Supplement: "Monochrome" and "Grayscale" in Modern Display Technology 

As colour display technology has become more popular, monochrome and greyscale monitors have slowly disappeared from the consumer market, but they are still very useful in professional areas. Some modern "monochrome monitors" now have basic grayscale functionality (such as 16 levels of greyscale) as part of the standard setting. This makes the difference between them and traditional grayscale monitors less clear. When buying, look at the "grayscale level" setting. The higher the level, the clearer the image and the more expensive it will be.  
 
In specialised fields like the military and aerospace, monochrome/grayscale displays are still very useful. This is because they can resist interference and can be used in extreme environments like very high or very low temperatures or strong radiation. Their "single color" design can actually reduce visual interference and improve information reading efficiency.