Protanopia · protan dichromacy
Protanopia (red-blind)
Without the long-wavelength L cones, red, green, brown, and orange are hard to tell apart, and red looks darker than it is.
- Missing cones
- L (long wavelength, red)
- Inheritance
- X-linked recessive
- Prevalence
- Men ~1.0% · women ~0.02%
- Neutral point
- ~492 nm (blue-green) looks gray
How it works
In protanopia, the L-cone photopigment (OPN1LW gene) is not produced or does not work, so color is judged with only two cone types, M and S — a form of dichromacy.
L cones also contribute heavily to the sense of brightness. That is why red light looks dimmer than it really is to someone with protanopia: deep red can look almost black, and red LEDs or brake lights can seem relatively faint.
Around 492 nm in the spectrum (blue-green) lies a neutral point that cannot be distinguished from white or gray.
What you see
Red, orange, yellow, and green collapse into similar yellowish-brown tones that differ only in brightness. Blue and purple look like nearly the same blue, because the red component of purple drops out.
The table below shows the same colors through a protanopia simulation. Notice how red and green, and blue and purple, move closer together.
| Color | Normal vision | Protanopia (red-blind) |
|---|---|---|
| Red | #D7263D | #5F583C |
| Orange | #F28C28 | #AB9712 |
| Yellow | #F2CD37 | #E3C915 |
| Green | #2E9E44 | #A0903B |
| Teal | #1A9E9A | #94959A |
| Blue | #2F6BD8 | #2578DC |
| Purple | #7E3FB2 | #005CB6 |
| Pink | #E86FA6 | #7F8AA8 |
| Brown | #8B5A2B | #695E26 |
| Gray | #8C8C8C | #8C8C8C |
Simulation: Machado, Oliveira & Fernandes (2009) matrices at 100% severity. Results may differ from reality depending on your monitor and individual differences.
How common is it?
It is reported in about 1.0% of men and about 0.02% of women of European ancestry (Sharpe et al., 1999). Because it is X-linked, men vastly outnumber women.
The overall rate of red-green deficiency varies across populations and is among the highest in men of European ancestry, at around 8% (Birch, 2012).
Easily confused colors
- Red ↔ green ↔ brown ↔ orange (especially when muted or dark)
- Blue ↔ purple, pink ↔ gray
- Deep red ↔ black (a hallmark of protan vision, in which red looks dark)
Everyday tips
- Red warning lights and laser pointers may be hard to see. When presenting, use a green laser or a highlighted cursor.
- Turning on the protan correction in your phone's color filters (iPhone “Accessibility → Display & Text Size → Color Filters,” Android “Accessibility → Color correction”) can make some colors easier to tell apart.
- When color names matter (clothes, cables, charts), making a habit of using labels or patterns helps. Everyday life guide