Browse Prior Art Database

Measurement of Flicker Produced by Visual Display Units

IP.com Disclosure Number: IPCOM000059921D
Original Publication Date: 1986-Feb-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Chaplin, R: AUTHOR [+2]

Abstract

In order to provide a method for measuring the flicker level present in visual display units (VDUs), a peripheral aggravation index is derived from sampling individuals' vision. The index so found is then used as a datum for a scale of peripheral aggravation. Certain parameters of flicker perception in humans are common and can be described by a characteristic shape in terms of frequency and magnitude. Other environmental variables such as time average luminance and spatial factors of the field of view are controlled by the technique described below. First, a percentile of population for the limit of flicker perception is created in the same environment that will later be used to carry out VDU flicker level measurements.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 45% of the total text.

Page 1 of 3

Measurement of Flicker Produced by Visual Display Units

In order to provide a method for measuring the flicker level present in visual display units (VDUs), a peripheral aggravation index is derived from sampling individuals' vision. The index so found is then used as a datum for a scale of peripheral aggravation. Certain parameters of flicker perception in humans are common and can be described by a characteristic shape in terms of frequency and magnitude. Other environmental variables such as time average luminance and spatial factors of the field of view are controlled by the technique described below. First, a percentile of population for the limit of flicker perception is created in the same environment that will later be used to carry out VDU flicker level measurements. From this datum, a set of lines of equivalent perception are drawn at intervals of population percentile (i.e., 80%, 90%, 95%) and this is used as the index. When a Fourier transform is performed on measurements of VDU output, the peaks of the transform can be matched against the index, and so each VDU can be classed by this population index number. A special photodetector and AGC (automatic gain control) amplifier are used to convert the VDU luminance modulation into a signal that can be output to a frequency analyzer. The peripheral aggravation index is created upon the following facts derived from experimental results. The characteristic which bounds the perception of flicker is the same for all persons. There are differences between individuals, which cause this characteristic to be shifted in the frequency domain, but it is possible to generalize about the population. For any individual the perception of flicker at constant time average luminance is proportional to the Fourier fundamental of PK-PK modulation. For the purposes of creating a peripheral aggravation index, the responses of controlled samples of the population are measured in order to establish the population distribution and the datum lines are constructed to form the index. In order that other variables affecting the perception of flicker remain constant, such that the characteristic datum can be correlated to the measurement devices, the following parameters are fixed. The average luminance of the experimental flicker source is the same as that used during VDU flicker level measurement, and is also that typically used under office conditions. In order that a measurement device may be calibrated to the flicker source, the source area is larger than that seen by the measurement device due to its acceptance angle. This requirement is met by using an optical system having a two-degree acceptance angle. Because sensitivity to flicker is worst when viewed peripherally, it is this characteristic which is used to create the index. The flicker source is composed of a 10 cm.sq. block of LEDs (light-emitting diodes) 1 representing 1/4 of an average graphic screen (Fig. 1). A current driver 2 is used...