Sunday, June 19, 2011

TEST FOR COLOUR BLINDNESS FOR GARNER TEST

GARNER  TEST :
                           Some principles to be followed in devising a test sufficiently sensitive to detect such differences have been described by the author 13 else where .These principles have since been used to construct a test which detects qualitatively and quantitatively differences in colour vision which exist amongst for example foreman dyers of proved ability in colour matching .Representative points on a colour triangle the corners of which are red yellow and blue are dyed with dyes which possess reflection spectra such that they tend to go greener in artificial light whilst test patterns are dyes in such a way that they go redder in artificial light.
  A match obtained by a normal person in north daylight on this test is not valid to him in any other light and the test is therefore of use in evaluating lamps put forward as suitable for colour matching. In one experiment a difference in the colour of the light from two commercial daylight matching lamps of the same make and supposedly identical was detected and found to be due to a difference in the age for the electric bulb in the two lamps.
          The reflectance spectra of two patterns which in this test match in north daylight to normal eyes differ in the red and green regions of the spectrum . Therefore a person who is colour weak with respect to green or red sees a difference in depth where the normal eye sees identity this difference in depth in depth is regather by the colour weak person as a difference in colour. The test detects cases of red green colour weakness which are mild enough to escape such tests as the Ishmael test .  It is also by its nature able to detest departures from normal due to yellowing of the lens or abnormal oracular pigmentation .
           The normal or mean match positions in the light of the Sc standard north daylight of the C I E 1,2 have been ascertained and are recorded on a chart for reference purposes . The test is issued together with would be obtained by a normal observer have been assessed and noted.
           The deviations from normal found by examination of a considerable number of individuals have been calculated into terms of standard deviation and a circle wotha radius of twice the standard deviation drawn round the mean match positions on the chart may be used in assessing the suitability or otherwise of an individual for employment as a colour matcher.