Yellow light is composed of a range of wavelengths in the visible light spectrum. When white light passes through a yellow filter, only certain wavelengths are transmitted while others are absorbed. This results in the perception of the color yellow. Understanding the composition of yellow light helps explain why certain objects appear yellow while others do not.
The Visible Light Spectrum
Visible light is part of the electromagnetic spectrum that can be detected by the human eye. The visible spectrum ranges from violet light with short wavelengths of around 380-450 nanometers to red light with longer wavelengths of around 620-750 nanometers. In between these extremes are all the colors of the rainbow.
The wavelength of light determines its color. Light at the red end of the spectrum has longer, lower frequency wavelengths while violet light has shorter, higher frequency wavelengths. Yellow light falls in the middle of the visible spectrum with dominant wavelengths generally between 570-590 nanometers.
Composition of Yellow Light
When white light encounters a yellow filter, the filter selectively absorbs all wavelengths except those around 570-590 nm. This stimulates the eye’s cone cells responsible for perceiving yellow hues. While yellow light is dominated by wavelengths around 580 nm, it also contains smaller amounts of adjacent wavelengths:
| Color | Wavelength range |
|---|---|
| Green | 495-570 nm |
| Yellow | 570-590 nm |
| Orange | 590-620 nm |
So technically, yellow light is not composed of a single wavelength but includes yellow-green, yellow, and yellow-orange wavelengths. The yellow component overwhelms the small amounts of green and orange light to give the appearance of monochromatic yellow.
Why Objects Appear Yellow
The color an object appears depends on which wavelengths of light it absorbs and which it reflects. A lemon appears yellow because it absorbs violet, blue, green, orange, and red light while reflecting predominantly yellow wavelengths.
When white light shines on a lemon, the lemon’s surface pigments absorb all colors except yellow. This reflected yellow light enters our eyes, stimulating yellow color perception in the brain. A lemon appears yellow regardless of the light source because its pigments selectively reflect yellow wavelengths.
However, not all yellow objects contain yellow pigments. Mixing red and green light creates the perception of yellow, even though the object emitting this light may lack yellow pigments. Computer screens and other light sources produce yellow through the additive mixture of red and green wavelengths.
Why the Sky and Sun Appear Yellow
During sunrise and sunset, the sun and sky often take on a yellowish hue even though the sunlight itself contains all visible wavelengths. This occurs due to the interacting effects of scattering and absorption in the atmosphere.
As sunlight enters Earth’s atmosphere at a low angle during twilight hours, the shorter wavelength violet and blue components get scattered and removed from the direct beam of light. This greater scattering of short wavelengths leaves behind more long-wavelength yellow and red light.
In addition, the low sun angle means the light must travel through more air mass. This gives atmospheric particles and gas molecules more opportunity to preferentially absorb the scattered violet and blue light.
The combined scattering and absorption filters out much of the blue light, allowing the yellow and red wavelengths to pass through. The dominance of these long wavelengths makes the sun and sky appear yellow or reddish rather than white during twilight.
Why Yellow Dominates Other Light Colors
When multiple colors of light mix, the resulting color is often skewed towards yellow. This is because yellow stimulates both the medium and long wavelength cone cells in the eye while other colors like blue only stimulate short wavelength cones.
The dual stimulation of cone cells makes yellow overpower colors like blue and violet when lights mix. For example, blue and green light shone together appears greenish-yellow rather than turquoise because yellow overwhelms blue in the color balance.
Yellow also dominates in the mixing of paint pigments. Mixing blue and red paint produces purple rather than an even blend. This is because paint absorbs certain colors rather than emitting light, so mixing paint colors follows different rules than mixing colored light.
Pure Yellow Light vs. Yellow Objects
It’s important to distinguish pure single-wavelength yellow light from yellow objects. Monochromatic yellow light ranging from 570-590 nm only stimulates the medium wavelength cones in our eyes without activating short or long wavelength cones.
But yellow objects contain hue mixtures and illuminate surroundings by reflecting light across many wavelengths. Pure yellow light is rare compared to the yellow hues we perceive from objects and multi-colored light sources.
Even sources like sodium vapor lamps that emit narrowband yellow light still produce some spread of wavelengths centered around 589 nm rather than a single precise yellow wavelength. Real-world yellow light is always composed of wavelengths spanning adjacent spectral bands that blend to be perceived as yellow.
Color Perception Under Yellow Light
Since yellow light contains a mixture of wavelengths, it illuminates surroundings differently than pure yellow monochromatic light. Under yellow light, objects that reflect yellow wavelengths well will appear closest to their true color. But surfaces reflecting mostly violet, blue, and green wavelengths may start to take on a dull or brownish cast since those colors are diminished in yellow light.
Yellow light mutes purple hues the most since it lacks the short wavelength blue components. Reds, oranges, and yellows come through more accurately under yellow lighting while blues and purples are subdued and shifted toward green or brown undertones.
This effect is evident under yellow-tinted streetlights. Yellow light suppresses the bluish wavelengths that normally brighten white surfaces at night. This can cause pale surfaces to appear dingy and yellowed rather than cleanly white.
Psychological Effects of Yellow Light
Extensive exposure to pure yellow light can have subtle psychological effects due to the lack of color contrast and visual stimulation. Studies suggest prolonged exposure to monochromatic yellow environments may induce boredom, feelings of isolation, and loss of concentration.
However, yellow light in more typical mixed lighting environments has positive psychological connotations. Yellow evokes cheerfulness, warmth, and energy without the overstimulating properties of shorter wavelength hues. The balance of stimulation from yellow light can create uplifting moods associated with sunshine and optimism.
But most psychological impacts of yellow spaces come from associations with yellow objects and settings rather than the wavelengths of yellow light itself. More research is needed on how exposure to narrowband vs. broadband yellow light influences emotions and performance.
Applications of Yellow Light
Yellow light serves an array of practical uses:
– Traffic lights – Yellow warns drivers to slow down in preparation for a red light. Yellow contrasts against both the red stop light and green go light for high visibility.
– Bug zappers – Insects are attracted to ultraviolet and yellow wavelengths. Bug zappers mimic these hues to lure insects toward the trapping wire grid.
– Safety lights – Yellow hazard lights provide high contrast against most environments without excessive glare. Yellow grabs attention while maintaining visibility better than bright white light.
– Underwater lighting – Since water absorbs long red wavelengths, yellow light penetrates to greater depths while allowing humans to see colors better than under blue light.
– Security lighting – Low-pressure sodium yellow lights preserve night vision and visual acuity better than higher intensity white lighting.
– Signage – Yellow captures attention and stands out against most backdrops. Black text on a yellow background gives optimal contrast for visibility.
Conclusion
Yellow light spans a narrow band of the visible spectrum around 570-590 nanometers. It contains traces of green and orange hues but is dominated by yellow wavelengths. This composition allows yellow to overpower other light colors in perception and gives yellow objects their characteristic color under white illumination. While pure yellow light is rare compared to multi-wavelength lighting, understanding yellow’s place in the spectrum helps explain many phenomena of color vision.
