Color vision

760, 380 nm

Light Waves & Vision: Light is made

up of energy waves that range from

__ to __ nm. These waves

stimulate the retina, sending signals

to the brain to create the sensation of

sight.

white light

When all these lightwaves are combined, we see ___

grating

When light passesthrough a prism or ___, it splitsinto different colors, forming the light spectrum

835 nm under ideal conditions.

Helmholtz observed wavelengths up to ___

Glancy and Graham

found the lower limit to be 320 nm, but seeing

this far into violet requires very intense light.

eye's lens, retina

The _____ and ____ can shift short wavelengths into longer ones, creating a lavender effect.

1. The eye absorbs certain wavelengths from sunlight.

2. Only 8% of visible light is absorbed.

3. Infrared rays are barely absorbed.

How the Eye Absorbs Light: (3)

1. Cornea absorbs wavelengths below 315 nm and completely blocks anything under 297 nm.

2. Lens starts absorbing at 400 nm and blocks everything below 300 nm.

3. Sunlight does not go beyond 290 nm.

Absorption by Eye Structures: (3)

1. Aging and cataracts can increase lens discoloration, making white light appear yellowish.

2. In cataracts, absorption may begin as early as 440 mu.

3. Short wavelengths between 400 and 350 mu are

   normally transformed by fluorescence into longer visible wavelengths.

Effects of Aging & Cataracts

Ludvigh, McCarthy (1938)

According to _____ and _____, only 10%

of violet light entering the human eye reaches the

retina. This partially prevents the harmful effects of

ultraviolet rays

• Hue

• Brightness

• Saturation

Color has (3) three main qualities:

Red, Orange, Yellow, Green, Blue (Indigo), and Violet.

Most people recognize 6-7 main hues. What are these?

intermediate shades

Colors gradually blend into one another, creating _____

5-7

With enough light and dispersion, a trained eye can detect many hues, but most people only distinguish around how many?

1. Recalling exact shades is difficult.

2. Everyday life doesn’t require naming many colors beyond the basics.

3. People often misidentify colors, like calling orange "yellow" or "reddish."

Why Do We Use Limited Color Names? (3)

discrimination, training, methodology

The number of colors one can distinguish depends on color _____, _____, and _______

more than 29 monochromatic patches

Edridge-Green: No individual could distinguish __________ in the spectrum.

55 distinct hues

Other studies: Up to ______ may be seen.

Koenig

Calculated 165 hues.

L. Jones

Identified 128 hues.

Laurens and Hamilton

Observed 207 hues.

approximate values

For easier recall, _______ are often used.

wavelength (nm)

In scientific work, colors are identified by their _______ for accuracy.

400, 800 trillion

Light waves range from ___ to _____ vibrations per second

all wavelengths of visible light

Light from the Sun (or any star) contains ______—this forms a continuous spectrum (like a rainbow).

outer layers of the Sun, Fraunhofer lines

As light passes through the _______, certain elements absorbspecific wavelengths, preventing thosecolors from reaching us. This creates dark lines in the spectrumwhere the absorbed light is missing—these are called ____

Hue discrimination

refers to the ability of the human eye to distinguish between different colors (hues). It is how well we can tell one color from another when they are very similar.

blue light

S-cones: Detect short wavelengths (____)

green light

M-cones: Detect medium wavelengths (____)

red light

L-cones: Detect long wavelengths (___)

two wavelengths are very close together, separate colors

Our brain processes the signals from these cones to interpret colors.

If _________, the brain struggles to tell them apart.

If they are farther apart, the brain easily distinguishes them as ______.

• Light intensity

• Color contrast

• Age

• Color vision deficiency (colorblindness)

Factors That Affect Hue Discrimination (4):

hue discrimination

Factors That Affect Hue Discrimination:

In dim light _____ decreases.

Light intensity, hue discrimination

Factors That Affect Hue Discrimination:

________

In dim light _____ decreases.

Color contrast, it’s harder to tell them apart

Factors That Affect Hue Discrimination:

________

If two similar hues are placed next to each other,

_________.

Age, blue colors

Factors That Affect Hue Discrimination:

________

As people age, their lens yellows, making ______ harder to distinguish.

Color vision defciency (colorblindness), red, green

Factors That Affect Hue Discrimination:

________

People with colorblindness have difficulty discriminating between certain hues (especially ___ and ____).

1. Size of retinal image.

2. Retinal region stimulated.

3. Condition of the retina.

4. Duration of stimulation.

5. Intensity of the light.

6. Purity, or saturation, of the color.

Factors Influencing Hue (6)

shades of gray, 0.25 meter-candle

How Light Intensity Affects Color Vision:

In low light, the eye sees everything in _____(no color).Color is only seen when light reaches at least _____

Achromatic Threshold

The minimum light needed to see anything (scotopic

vision).

Chromatic Threshold

minimum light needed to see color (photopic

vision).

Photochromatic Interval

The gap between these two levels of light

intensity. (chromatic and achromatic threshold)

achromatic threshold, photochromatic interval

In dark adaptation, the ______ lowers, making the ______ longer.

1. Blue

2. Green

3. Yellow

4. Red (last to appear)

As light gradually increases, colors appear in this order (4):

Duplicity Theory

describes how rods and cones process light differently.

Critical Frequency Method (Flicker Photometry)

Measures brightness by testing how colors flicker at different light intensities.

Direct Comparison Method

A spectral color is compared to white light, adjusting its intensity until they appear equally bright.

Direct Comparison Method, Critical Frequency Method (Flicker Photometry)

Methods to Measure Brightness

1. Yellow

2. Orange

3. Green

4. Red

5. Blue

Heterochromatic Photometry

Brightness Ranking (Highest to Lowest)

Also known as ______.

Flicker Photometry

measures the relative brightness of two colors.

The Photopic Curve

shows how brightness changes across wavelengths.

yellow region

Maximum Brightness: Found at 580 nm (____)

red, violet

Brightness drops sharply in the ___ and ___ ends of the spectrum.

faster

The longer wavelengths (red) fade ____ than the shorter ones.

556 nm (yellow-green)

Energy Requirements for Light Perception

___requires the least energy (~0.0015 watts per lumen).

Red & blue-green

Energy Requirements for Light Perception

___need 10x more energy.

Extreme red & violet

Energy Requirements for Light Perception

___10,000x more energy

yellow, yellow-green

The eye is highly sensitive to ___ & _____light, adapting over time for efficient vision.

brightness

As light intensity decreases, _____ also decreases.

light intensity drops significantly.

The luminosity curve stays the same until _______

610 nm (red-orange) to To 535 nm (green)

When intensity falls below 0.25 meter-candle, the brightness peak shifts from ______ to ____

Red, blue

THE PURKINJE SHIFT

In daylight: ___ appears brighter than ___.

0.25 meter-candle

THE PURKINJE SHIFT

In dim light: Red remains brighter until light drops below ______.

Blue, red

THE PURKINJE SHIFT

In very low light: ____ becomes brighter than ___.

When light increases again

THE PURKINJE SHIFT

______: Red regains its brightness over blue.

fovea

Scotopic vision (low light) is rod-based, requiring rhodopsin, which is absent in the ____.

cone-based

Fovea is mostly _____, so it does not show this effect as strongly.

Saturation

refers to how pure a color is, meaning its freedom from white light.

No white light present

100% Saturation = _____

1. Adding white light to red turns it into pink

2. As more white is added, the color becomes paler.

3. Too much white makes the hue disappear completely.

How White Light Affects Color (3)

solar spectrum

Spectrum Colors in the ____ are not perfectly saturated.

vivid colors

It’s possible to see more ____ than those found in the spectrum.

red

During scotopic vision, all colors (except __) are seen as untoned.

hues, saturation

During photopic vision, ___ appear with increasing light intensity, and ___ increases to a maximum before decreasing again as hues fade into untoned white.

1. Red (first to fade)

2. Yellow

3. Green

4. Blue (last to fade)

As illumination decreases, colors disappear in this order:

440, 565

Wavelengths Saturation peaks at specific light intensities for different wavelengths:

___ nm (blue-violet) → 9 photons of illumination.

___ nm (yellow) → 219 photons of illumination.

fovea, periphery

FieldsThe retina’s sensitivity varies from the ____ to the ____.

Isoptera

Used to map retinal sensitivity to different light intensities.

photochromatic interval

exists between color perception and the peripheral colorless field.

1. Condition of the Retina

2. Intensity of the Light

3. Size of the Test Object

4. Surrounding Field Conditions

Factors Influencing Retinal Sensitivity (4)

Trichromacy

______ or Normal colour vision uses all three types of cone cells which arefunctioning correctly.

anomalous trichromats

People with ‘faulty’ trichromatic vision will be colour blind to someextent and are known as _____.

Severe color blindness

occurs when all three cone cells are absent.

Mild color blindness

happens when all three cone cells are present but one cone cell does not work right.

1. Retinal detachment

2. Eye injuries caused by lasers

3. Some kinds of brain tumors

Some examples of injuries that can lead to color visiondeficiency are: (3)

cataracts

Color vision may also get worse as you get older — often because of ____

Deuteranomaly

is the most common type of red-green color vision deficiency. It makes certain shades of green look more red. This type is mild and doesn’t usually get in the way of normal activities.

Protanomaly

makes certain shades of red look more green and less bright. This type is mild and usually doesn’t get in the way of normal activities.

Protanopia and deuteranopia

both make someone unable to tell the

difference between red and green at all.

Tritanomaly,

Tritanopia

There are 2 types of blue-yellow color vision deficiency:

Tritanomaly

makes it hard to tell the difference between blue and green and between yellow and red.

Tritanopia

makes someone unable to tell the difference between blue and green, purple and red, and yellow and pink.

monochromacy, achromatopsia

If you have complete color vision deficiency, youcan’t see colors at all. This is also called ____ or ____, and it’s rare.