CHAPTER 11: LIST OF EQUATIONS

Determining the Appropriate Luminance Uniformity within an Icon

Perent Element	(Luminance min) - (Luminance max)	(1)
=
Nonuniformity	(Luminance max)
where
Luminance max = the smaller luminance value Luminancemin = the greater luminance value

Determining the Appropriate Contrast within an Icon

We define contrast as a ratio between maximum and minimum luminance values, or:	(2)
Contrast ratio =      Luminance max
	Luminance min
where:
Luminance max = luminance emitted by the area or element of greater intensity Luminance min = luminance emitted by the area or element of smaller intensity

Determining the Appropriate Size of Icon Components

If Known	Use These Formulas for Calculating These Known Years
	Visual Angle	Symbol Height	Distance
Distance and Symbol Height	(3) (4)
Distance and Visual Angle		Distance x [Tangent (Visual Angle)] (5)
Visual Angle and Symbol Height			Symbol Height Tangent (Visual Angle) (6)

where:
Symbol Height = the Height of the symbology
Distance = distance from viewer's eyepoint to the display
Visual Angle = angle in degrees
Height and Distance use the same unit of measure (e.g., meters, yards, etc.)

Determining The Effects of Icon Legibility

S=KO^m

Perceived Urgency of Auditory Signals

Example of Using Steven's Power Law for Producing Urgency Exponents (see references 2 and 3 for more detailed explanations and examples)
S=kOm	(8)

Timing of Auditory Navigation Information

Equations for Determining the Appropriate Timing of an Instruction

---

Previous  | Table of Contents |  Next

FHWA-RD-03-065

---

TFHRC Home | FHWA Home | Feedback United States Department of Transportation - Federal Highway Administration