Comparing CRT, LCD, LED, and Plasma displays reveals distinct technologies used to create images, each with its own strengths and weaknesses.
These display types differ fundamentally in how they generate light and color to form the picture you see.
CRT: The Classic Tube Display
- How it Works: Cathode Ray Tube (CRT) displays use an electron beam fired onto a phosphor-coated screen. The electron beam scans across the screen, illuminating the phosphors, which glow to create the image. Different phosphors emit red, green, or blue light.
- Characteristics: Known for excellent motion handling and contrast, but are very large, heavy, and consume significant energy.
LCD: The Liquid Crystal Barrier
- How it Works: Liquid Crystal Displays (LCDs) use a layer of liquid crystals sandwiched between two polarized glass panels. A backlight provides the light source (typically CCFLs - Cold Cathode Fluorescent Lamps, in older models). The liquid crystals act like shutters, twisting or untwisting to block or allow light from the backlight to pass through color filters, creating the pixels.
- Characteristics: Thinner and lighter than CRTs, more energy efficient than CRTs and Plasma. Performance can vary greatly depending on the panel type (TN, VA, IPS) regarding viewing angles, color accuracy, and response time.
LED: LCD with an Improved Backlight
- How it Works: Light Emitting Diode (LED) displays are essentially a type of LCD display that uses LEDs instead of CCFLs as the backlight. As noted in the reference, "LED (Light Emitting Diodes) - each pixel is 3 little LED lamps" (referring to the underlying light source structure), offering improvements over traditional LCDs. The light from these LEDs is then filtered by liquid crystals and color filters, just like a standard LCD.
- Characteristics: Offer improved brightness, contrast, and color accuracy compared to CCFL-backlit LCDs. According to the reference, LED displays are also "Brighter, less energy [than CRT]". They are very thin and have become the dominant consumer display technology.
Plasma: The Tiny Fluorescent Lamps
- How it Works: Plasma displays use millions of tiny cells filled with an inert gas mixture. An electric current excites the gas, causing it to release ultraviolet (UV) light. This UV light then stimulates red, green, and blue phosphors on the inside walls of the cells, making them glow and create visible light for each pixel. As highlighted in the reference, "Plasma - each pixel is a little flourescent lamp."
- Characteristics: Known for deep blacks, high contrast ratios, wide viewing angles, and excellent motion handling. However, they can consume more energy than LCD/LED, can be susceptible to screen burn-in, and contain glass panels which can be reflective and heavy.
Key Differences Compared
Here's a breakdown of the primary distinctions between these display technologies:
How Images Are Created
- CRT: Electron beam striking phosphors.
- LCD/LED: Backlight filtered by liquid crystals. (LED uses LED backlight).
- Plasma: Gas cells containing phosphors emitting light. (Reference: "Plasma - each pixel is a little flourescent lamp.")
Energy Consumption
- CRT: Very high.
- LCD: Moderate.
- LED: Low, less energy than CRT, as stated in the reference.
- Plasma: High (can vary based on content, darker images use less power).
Brightness and Contrast
- CRT: Good brightness, high contrast.
- LCD: Moderate brightness and contrast (dependent on panel type and backlight).
- LED: High brightness, often better contrast than traditional LCDs (especially with local dimming), and as the reference notes, Brighter than CRT.
- Plasma: High brightness, excellent contrast (especially black levels).
Motion Handling & Viewing Angle
- CRT: Excellent motion handling, wide viewing angles.
- LCD/LED: Good motion handling (can vary), viewing angles can be limited on some panel types (like TN).
- Plasma: Excellent motion handling, wide viewing angles.
Size, Weight, and Design
- CRT: Large, heavy, bulky.
- LCD/LED: Thin, lightweight, flat panel.
- Plasma: Relatively thin and flat, but often heavier than comparable LCD/LED screens due to glass panels.
Lifespan and Practical Considerations
- CRT: Decent lifespan, but bulky and obsolete for new manufacturing.
- LCD/LED: Long lifespan, immune to burn-in (though image retention is possible). Dominant modern technology.
- Plasma: Decent lifespan, but susceptible to screen burn-in (though less of an issue with modern models), contains mercury, and production has largely ceased for consumer TVs.
Quick Comparison Table
| Feature | CRT | LCD | LED | Plasma |
|---|---|---|---|---|
| Image Source | Electron Beam on Phosphor | Backlight filtered by LC | LED Backlight filtered by LC | Gas Cells with Phosphors |
| Pixel Basis | Phosphor dots illuminated | LC blocking/passing light | LC blocking/passing light | Gas discharge exciting phosphor ("little flourescent lamp") |
| Energy Use | Very High | Moderate | Low ("Less energy than CRT") | High |
| Brightness | Good | Moderate | High ("Brighter" than CRT) | High |
| Contrast | High | Moderate | Good to High | Excellent |
| Motion Hdl. | Excellent | Good | Good | Excellent |
| Viewing Angle | Wide | Variable | Variable | Wide |
| Size/Weight | Bulky/Heavy | Thin/Light | Thin/Light | Thinner/Heavier than LED |
| Burn-in | No | No (Image Retention possible) | No (Image Retention possible) | Yes (Susceptible) |
| Current | Obsolete | Largely replaced by LED | Dominant Consumer Tech | Largely Obsolete for Consumer |
Conclusion
In summary, the difference between CRT, LCD, LED, and Plasma lies in their core technology for generating images. CRTs used electron beams, LCDs and LEDs use a backlight filtered by liquid crystals (with LED using more efficient and brighter LEDs as the backlight, consuming less energy than CRT), and Plasma uses gas-filled cells that excite phosphors ("a little flourescent lamp" per pixel) for light emission. While CRT and Plasma offered excellent image quality in their prime, their energy consumption, size/weight, and susceptibility to burn-in (Plasma) led to the rise of the more energy-efficient, thinner, and versatile LCD/LED technologies, which now dominate the display market.
