Farnsworth Lantern
I don't have a link, but the procedures I use are:
Operation of the Test. Points on the operation of the lantern are as follows:
(1) It is important that the FALANT be used through the step-down transformer supplied and not plugged directly into a 240 V power outlet.
(2) The test should be performed in a normally lighted room. The room should be screened from glare and exclude sunlight. The applicant should not face the source of room illumination.
(3) Only one applicant should be tested at a time (others should not be allowed to watch).
(4) The applicant should be positioned 2.5 metres from the lantern.
(5) The applicant may stand or sit. If glasses are used for distance, they should be worn. The aperture of the lantern should be directed at the head of the applicant and the adjusting screw should be tightened to hold the lantern in this position.
(6) The examiner must be CP1.
Conduct of the test. The test is to be conducted as follows:
(1) The examiner should inform the applicant that, ‘the lights you will see in this lantern are red, green or white. They look like signal lights at a distance. Two lights are presented at a time in any combination, one above the other. Call out the colours as soon as you see them, naming the colour at the top first and then
the colour at the bottom. Remember, only three colours, red, green and white—and top first’.
(2) The examiner should turn the knob at the top of the lantern to change the lights. To expose the lights, the button in the centre of the knob should be depressed. The examiner should maintain regular timing of about two seconds per exposure.
(3) The lights should be exposed in random order, starting with an RG (red, green) or GR (green, red) combination (Nos 1 or 5), continuing until each of the nine combinations has been exposed.
(4) If the applicant says ‘yellow’, ‘pink’, etc. the examiner should remind them that ‘there are only three colours—red, green and white’.
(5) If the applicant takes a long time to respond, the examiner should inform them ‘as soon as you see the lights, call them’.
Scoring of the test. The test is to be recorded and scored
as follows:
(1) An error is considered the miscalling of one or both of a pair of lights.
(2) If no errors are made on the first run of nine pairs of lights, the applicant is passed.
(3) If any errors are made on the first run, discard the results of the first run and give two more complete runs.
(4) Add the errors of these last two runs. Two errors or less represents a pass (CP2), more than two errors a fail (CP3).
Hope this helps.
Cheers,
BM