Problem 7 - Biological Psychology

Question

When a television set is off, its screen appears gray. When you watch a program, parts of the screen appear black, even though more light is actually showing on the screen than when the set was off. What accounts for the black perception?

Step-by-Step Solution

Answer

The 'black' areas block or emit less light, creating a contrast that our brain perceives as black.

Step 1: Understanding The Television Screen

When a television screen is off, it appears gray because the screen is reflecting ambient light in the room. This reflection gives the screen its gray appearance.

Step 2: Analyzing The 'Black' Areas

When the television screen is on and displaying a program, certain parts appear black due to how the screen emits light. LCD and LED screens use pixels to control the color and brightness of the display.

Step 3: Black Pixels Explained

In these pixels, when the screen wants to show black, it actually blocks the light (in the case of LCD, using liquid crystals) or turns off the light (in the case of OLED). Therefore, less light is emitted in these areas, even though the backlight is still on in most LED TVs.

Step 4: Perception of Black Color

The brain perceives these lower light-emission areas as 'black,' because they emit much less light than other parts of the screen. The contrast between those areas and the bright parts of the screen makes them appear blacker than the initial gray of the turned-off screen.

Key Concepts

Television Screen Technology

Television screen technology has come a long way from the bulky cathode ray tubes (CRT) to the sleek LCD and OLED screens we use today. This advancement in technology improves how we perceive images on the screen. LCD screens use liquid crystal displays to modulate light, while OLED screens use organic compounds that emit light when electricity is applied. This allows for a broader range of colors and sharper images.

With LCD technology, a backlight shines through the liquid crystals that arrange to alter the passage of light to form images. In the case of OLED, each pixel is its own light source, creating deeper blacks and a more vivid display. These technologies help the TV screen portray realistic scenes with a higher contrast ratio than older technology.

Light Emission

Light emission plays a crucial role in how we see colors on a television screen. In an LCD television, the backlight (often composed of LED lights) provides the necessary illumination. The liquid crystals modulate this light to display various colors.

In contrast, OLED screens emit light on a pixel-by-pixel basis. This allows for precise control over which areas are illuminated, resulting in deeper blacks and sharper contrasts.

• LCD requires a consistent backlight.
• OLED has individual pixel lighting control.

The control of light in these displays is why they can make dark areas appear much darker, improving the overall viewing experience.

Visual Perception

Our perception of color and 'blackness' on a television screen is shaped by how our brains process visual information. When light is emitted from the screen into our eyes, our brain interprets the signals. We perceive an area on the screen as black if it emits significantly less light compared to other areas, even if some light is still present.

This phenomenon is due to the high contrast between light and dark areas of the screen. The human eye is more sensitive to contrast than to the absolute amount of light, which allows us to perceive detailed colors and shades. The contrast adaptation of our visual perception means that darker screen sections appear blacker when surrounded by brighter areas. This is why even with some light emission, the brain perceives parts of the screen as truly black.