Module 4 Part 1: Light - The Physical Stimulus

Why Does Vision Matter in Human Factors?

Much of the information people use to interact with systems is presented visually.

3 Reasons Why Vision Matters in Human Factors

1. Detect: can the user see it?

2. Interpret: can the user understand it?

3. Find: can the user locate what matters?

5 Stages from Light to Visual Search

1. Light/Physical Stimulus.

2. Eye: detect & transduce.

3. Perception: organize & interpret.

4. Attention: select information.

5. Visual Search: find what matters.

Definition: Light

a wave of electromagnetic energy, represented as a point on the visible spectrum.

Fill in the blank: BLANK (nm) determines BLANK (color).

Wavelength (nm) determines hue (color).

T/F: Physical Stimulus does not equal Perceptual Experience.

T

What are the 2 characteristics associated with Physical Characteristics (of the stimulus)?

1. Wavelength (nm).

2. Intensity (amount of energy).

What are the 2 characteristics associated with Perceptual Experience (of the observer)?

1. Hue (color).

2. Brightness (how bright it appears).

Definition: Psychophysics

the study of the relationship between the physical properties of a stimulus and the perceptual experience it produces.

What are the 3 measurements of lights and their units?

1. Luminous Flux (lumens; lm).

2. Illuminance (lux; lx).

3. Luminance (candelas per m², cd/m²).

Definition: Luminous Flex (measured in lumens; lm)

quantifies the total amount of visible light emitted by a source.

What are the 3 measurements and their relationship to light?

1. Luminous Flux (lumens; lm) → source

2. Illuminance (lux; lx) → surface

3. Luminance (candelas per m², cd/m²) → eye

What are the 3 descriptions of light and their definitions?

1. Source: emits light.

2. Surface: receives light.

3. Eye: sees reflected/emitted light.

Definition: Illuminance (measured in lux; lx)

how much light is hitting a surface.

Definition Luminance (measured in candelas per m²; cd/m²)

amount of light emitted or reflected from a surface and perceived by the eye.

What is the main difference between Illuminance and Luminance?

illuminance (lx) is about the light arriving at a surface, while luminance (cd/m²) about the light leaving a surface and reaching your eyes.