Red-cone color vision difference
Short answer
Protan color blindness affects the red-sensitive cone signal. Reds may appear darker and some red-green differences become harder to distinguish.
Online mild or strong labels are estimates, not clinical diagnoses.
In detail
Protan color blindness is a red-green color vision difference involving the long-wavelength-sensitive L-cone photopigment. Protanomaly changes its response; protanopia lacks a separate functioning L-cone signal.
Both can make red-green differences harder to distinguish, and reds can appear less bright. The type and degree suggested by an online test are estimates, not a clinical assessment.
Protan vision does not usually mean a black-and-white world. Some reds, greens, browns and oranges become harder to separate. The exact confusion depends on the shades, their brightness, the background and the individual. A color name alone cannot predict whether a particular object will be distinguishable.
Dark red against black can be especially difficult because protan vision reduces sensitivity to long-wavelength light. In a chart or interface, add labels, symbols or different line styles instead of relying on a red-green distinction. Our color blindness simulator illustrates possible confusions; it cannot reproduce every person's experience.
Protan involves the long-wavelength L-cone signal; deutan color blindness involves the medium-wavelength M-cone signal. Both belong to the red-green family. Reduced red brightness is more characteristic of protan, but it is not enough to identify your type yourself.
Use protan vs deutan for a side-by-side comparison. This page explains protan on its own; the red-green guide covers the wider family.
A result such as mild protan, moderate protan or strong protan describes how you performed on that particular test. It is not a universal scale: different tests use different tasks and cutoffs, and an uncalibrated screen adds uncertainty. Read it as an estimate rather than a precise measure of everyday ability.
A strong label does not establish protanopia, and a mild label does not confirm protanomaly. Those names describe different color-vision mechanisms, not simply adjacent score bands. An online score cannot tell you whether a cone photopigment is absent.
If two tests disagree, compare their methods and viewing conditions rather than choosing the label you prefer. Keep your usual prescription lenses on, remove tinted lenses, and turn off display color filters. An eye-care professional can investigate an uncertain result with appropriate tests; an online label cannot determine eligibility for a job or license. See protan vs deutan for the distinction between the two families.
An online plate or arrangement test can provide a starting point for a conversation with an eye-care professional. A clinician can choose color plates, hue-arrangement tasks or an anomaloscope when a result needs clarification. A browser test on an uncalibrated display does not establish a clinical subtype.
Inherited red-green differences are generally lifelong. A new or noticeable change in color vision should be assessed rather than assumed to be inherited protan deficiency. For driving or work, use the relevant authority's required examination, not an online mild or strong label. Our career guide links to role-specific information.
Explore a possible color vision difference, then discuss an uncertain result with an eye-care professional.
Your screen and viewing conditions affect results. This is not a clinical or occupational examination.
Last reviewed October 22, 2026. Educational information, not a diagnosis. Online type and severity labels are estimates.