Anomaloscope
An anomaloscope or spectral color mixer is an optical instrument with which the color differentiation in red-green vision can be assessed and thus red-green color visual impairment can be diagnosed. It is also used for proficiency testing for bus drivers , train drivers , pilots , police officers , boat drivers , electricians and other professions.
The test person looks with one eye through an eyepiece at the test field, on which a circle divided horizontally into two halves is shown. On the lower half (yellow field), a spectral yellow (589.3 nm, middle of the two yellow Na lines) is presented as a reference field. On the upper half (mixed field) a spectral red (671 nm, Li line) and a spectral green (546.1 nm, Hg line) can be mixed by turning a fine drive, so that the color-savvy person in the mixed field has one with the Comparison field can set or “accept” a matching yellow tint, so that a completely yellow circle is created.
The green weak ( deuteranomal ) will add too much green in the upper semicircle, a red weak ( protanomal ) will add too much red.
There are various manufacturers of anomaloscopes, but they all work on the principle of the spectrometer .
The specifications for an anomaloscope were regulated by DIN standard 6160. However, this standard was withdrawn.
In addition to anomaloscopes for red-green assessment - the most common and most important from a safety point of view (traffic lights, railway signals) - there are also anomaloscopes that measure blue vision.
Nail anomaloscope
With the Willibald Nagel anomaloscope, the red gap for the mixed field is closed and the green gap is fully open when the position is “0”. With a position of “73”, the red gap is opened to the maximum and the green gap is closed. The yellow comparison scale is normally set to 15 graduation lines and is used to regulate the brightness of the yellow comparison field. The color-savvy sets a value of about 40 on the fine drive, the protanomal more, the deuteranomal much less.
Anomaly quotient
A quantitative measure results in an anomaly quotient (AQ, also: anomaly quotient ), which is calculated from the mean value of repeated settings (P) of the test subject (Vp) compared to the settings (N) of color-savvy people (No) according to the Rayleigh equation : AQ = [(73 - P) / P]: [(73 - N) / N]
This corresponds to the relationship: AQ = green component Vp x (red component No [= 40]) / red component Vp x (green component No [= 33])
Color-savvy people are in a range of AQ = 0.7–1.4. For protanomals an AQ of 0.1–0.6 results with P values> 40. For Deuteranomals an AQ of 2–20 with P values <40 results with a mean value of 3.0. In the case of color anopsies , specifying an anomaly quotient is meaningless; purely mathematically, it can assume all values from 0 to infinity.
In the case of protanopes, lights in the wavelength range of 500 nm excite the two remaining components in roughly the same way, which is why the sensation is colorless or gray. In the even longer-wave spectral range, only one component is excited to a different extent. The color differentiation is then only made according to the brightness. The curve of the spectral sensitivity is shifted towards the short-wave side. The maximum perception is not yellow, but more in the yellow-green range.
In the case of deuteranopes, the sensitivity curve for brightness is not shifted, and there is no restriction in the red range.
Some rules of thumb apply, including changes to the yellow setting:
- The so-called mean standard equation (40/15 = mixed field / yellow field) is assumed not only for normal trichromats but also for protanopes and deuteranopes.
- An end equation (pure green = 0 in the mixed field or pure red = 73 in the mixed field) is assumed by protanopes and deuteranopes in contrast to color-savvy people with variation of the yellow screw:
- Protanopes set a lighter yellow (G about 30–40) than deuteranopes in the green field (setting 0 in the mixed field).
- Protanopes set a darker yellow (G = 1–4) in the red field (setting 73 in the mixed field) than deuteranopes, the loss of brightness towards red is characteristic of protanopia.
- Deuteranopes leave the yellow screw area largely at 14-17.
- Anomalous trichromatism (deuteranomaly, protanomaly): Anomalous trichromats reject the mean standard equation.
- Rule of thumb for Deuter anomalies = 20/15.
- Rule of thumb for protanomals = 60/10.