Visible Light Wavelength and Colors: Complete Spectrum Guide

The Visible Spectrum

The visible spectrum is the range of electromagnetic wavelengths that the human eye can detect and interpret as color. It lies between ultraviolet (shorter wavelengths) and infrared (longer wavelengths) in the electromagnetic spectrum.

Wavelength Range

The boundaries of visible light are not sharply defined because sensitivity varies between individuals and decreases gradually at the edges. Generally accepted ranges are:

• Violet: 380-450 nm (shortest visible wavelength)
• Blue: 450-495 nm
• Green: 495-570 nm
• Yellow: 570-590 nm
• Orange: 590-620 nm
• Red: 620-700 nm (longest visible wavelength)

The mnemonic "Roy G. Biv" (Red, Orange, Yellow, Green, Blue, Indigo, Violet) helps remember the order from longest to shortest wavelength. Note that the traditional inclusion of indigo as a separate color was Newton's choice to create seven colors, matching musical notes and days of the week.

Frequency and Energy

Using the wave equation (c = fλ) and the photon energy equation (E = hf), we can calculate the frequency and energy associated with each color:

Higher frequency (shorter wavelength) light carries more energy per photon. This is why ultraviolet light, just beyond the violet end of the spectrum, can cause sunburn and damage DNA, while infrared (beyond red) produces heat but less chemical damage.

How We Perceive Color

Color perception is a complex process involving both physics (the wavelength of light) and biology (how our eyes and brain interpret signals).

The Human Eye

The retina contains two types of photoreceptor cells:

• Rods: Approximately 120 million cells that detect light intensity (brightness) but not color. Active in low light conditions (scotopic vision).
• Cones: Approximately 6-7 million cells that detect color. Active in bright light conditions (photopic vision).

Trichromatic Vision

Humans have three types of cone cells, each most sensitive to a different range of wavelengths:

The brain interprets the relative stimulation of these three cone types to perceive the full range of colors. This is why displays and printers use three primary colors (RGB for light, CMY for pigments) to create millions of colors.

Color Mixing

When multiple wavelengths reach the eye simultaneously, the brain perceives a combined color:

• Additive mixing (light): Red + Green = Yellow; Red + Blue = Magenta; Green + Blue = Cyan; All three = White
• Subtractive mixing (pigments): Yellow + Cyan = Green; Yellow + Magenta = Red; Cyan + Magenta = Blue; All three = Black

White light, such as sunlight, contains all visible wavelengths in roughly equal proportions. A prism separates white light into its component wavelengths, creating the familiar rainbow spectrum.

Detailed Wavelength-Color Reference

Here is a more detailed breakdown of wavelengths and their corresponding colors:

Note: Hex codes are approximations since computer displays cannot perfectly represent spectral colors. Pure spectral colors lie outside the gamut of RGB displays.

Spectral Colors vs. Non-Spectral Colors

Not all colors we perceive correspond to single wavelengths. Colors can be divided into two categories:

Spectral Colors

These are "pure" colors corresponding to single wavelengths in the visible spectrum. They appear in rainbows and can be produced by prisms or diffraction gratings. Examples include:

• Monochromatic red light at 650 nm
• Monochromatic green light at 530 nm
• Laser light at specific wavelengths

Non-Spectral Colors

These colors cannot be produced by a single wavelength and require mixing multiple wavelengths. Examples include:

• Magenta: Requires both red (~700 nm) and blue (~450 nm) wavelengths simultaneously
• Pink: Red wavelengths mixed with white light (all wavelengths)
• Brown: Low-intensity orange with context-dependent perception
• White: All visible wavelengths combined
• Gray: Reduced intensity of all wavelengths
• Black: Absence of visible light

Magenta is particularly interesting because it has no corresponding single wavelength. It appears on the "line of purples" connecting the red and violet ends of the spectrum in color space diagrams.

Light Sources and Their Spectra

Different light sources produce different spectral distributions, affecting how colors appear under various lighting conditions.

Incandescent Bulbs

These produce light by heating a filament until it glows. The spectrum is continuous, similar to sunlight but shifted toward longer wavelengths (more red/orange, less blue). Color temperature is typically 2700-3000K, appearing "warm."

Fluorescent Lights

These produce light through phosphor excitation. The spectrum consists of several emission peaks rather than a continuous distribution. This can cause some colors to appear different than under sunlight, a phenomenon called metamerism.

LEDs

Light-emitting diodes produce narrow-band emission. White LEDs typically use a blue LED with yellow phosphor coating, resulting in peaks at blue and yellow wavelengths with a gap in between. This can affect color rendering accuracy.

Common Light Source Wavelengths

Color Temperature and Blackbody Radiation

Color temperature describes the color of light produced by a heated object (blackbody radiator) at a specific temperature, measured in Kelvin (K).

Color Temperature Scale

Peak Wavelength Calculation

Wien's displacement law relates the peak emission wavelength to temperature:

Example: The Sun's surface temperature is approximately 5778K:

λ_peak = 2,898,000 / 5778 = 501 nm (green light)

This explains why human eyes evolved peak sensitivity in the green region; it matches the Sun's peak output.

Rainbows and Natural Color Phenomena

Natural phenomena demonstrate the relationship between wavelength and color in beautiful ways.

Rainbows

Rainbows form when sunlight is refracted and reflected inside water droplets. Different wavelengths refract at different angles, separating the colors:

• Red light (longer wavelength): refracts less, appears on the outside of the arc (about 42 degrees from the antisolar point)
• Violet light (shorter wavelength): refracts more, appears on the inside (about 40 degrees)

Secondary rainbows occur from double reflection inside droplets, appearing outside the primary rainbow with reversed color order.

Sunsets and Sunrises

The sky's color changes throughout the day due to Rayleigh scattering. Shorter wavelengths (blue, violet) scatter more than longer wavelengths (red, orange):

• Midday: Blue light scatters in all directions, making the sky appear blue
• Sunrise/Sunset: Light travels through more atmosphere, scattering away most blue light and leaving red/orange

Why the Sky Isn't Violet

Although violet light scatters even more than blue, the sky appears blue because: (1) sunlight contains less violet than blue, (2) our eyes are more sensitive to blue than violet, and (3) some violet is absorbed by the upper atmosphere.

Iridescence

Thin-film interference creates iridescent colors in soap bubbles, oil slicks, and butterfly wings. When light waves reflect from the top and bottom surfaces of a thin film, they interfere constructively or destructively depending on wavelength and viewing angle, producing shifting color patterns.

Applications of Visible Light Wavelengths

Display Technology

Modern displays use combinations of red, green, and blue light to create images:

• LCD: Uses white backlight filtered through color pixels, typically red (630 nm), green (530 nm), blue (450 nm)
• OLED: Each pixel emits its own light, allowing deeper blacks and wider viewing angles
• Quantum dot: Uses nanoparticles to produce precise, saturated colors

Photography and Cinematography

Understanding wavelength helps photographers:

• Match white balance to lighting conditions
• Use color filters to enhance or reduce certain wavelengths
• Select appropriate lighting for accurate color reproduction
• Understand why certain color combinations work well together

Medical Applications

Different wavelengths have specific medical uses:

• Blue light (420-480 nm): Treatment of jaundice in newborns, acne therapy
• Green light (500-570 nm): Laser treatment of vascular conditions, enhanced visualization during surgery
• Red light (620-700 nm): Photobiomodulation therapy, wound healing promotion
• Near-infrared (700-1000 nm): Deep tissue therapy, photodynamic therapy

Plant Growth

Plants use specific wavelengths for photosynthesis:

• Blue light (400-500 nm): Absorbed by chlorophyll a, important for vegetative growth
• Red light (600-700 nm): Absorbed by chlorophyll b, crucial for flowering and fruiting
• Green light (500-600 nm): Mostly reflected (why plants appear green), some contribution to photosynthesis

LED grow lights are designed to emit primarily red and blue wavelengths, optimizing energy efficiency for plant growth.

Optical Communications

While fiber optic communications typically use infrared (1310 nm, 1550 nm), visible light communication (VLC) or "Li-Fi" uses visible wavelengths for short-range data transmission using LED lighting.

Color Vision Deficiencies

Approximately 8% of men and 0.5% of women have some form of color vision deficiency, affecting how they perceive wavelengths.

Types of Color Blindness

Color blindness is inherited through genes on the X chromosome, explaining why it's more common in males (who have only one X chromosome). People with color vision deficiencies can often still distinguish colors by brightness differences.

Measuring Wavelength: Spectroscopy

Spectroscopy is the study of how matter interacts with light at different wavelengths, enabling precise wavelength measurement.

Spectrometer Components

• Light source: Provides illumination (broadband or specific wavelengths)
• Dispersive element: Prism or diffraction grating separates wavelengths
• Detector: Measures intensity at each wavelength (photodiode, CCD, photomultiplier)

Emission and Absorption Spectra

Every element has a unique spectral "fingerprint":

• Emission spectra: Heated elements emit light at specific wavelengths (bright lines on dark background)
• Absorption spectra: Cool elements absorb specific wavelengths from continuous light (dark lines on bright background)

Notable Spectral Lines

Wavelength Calculations

Example 1: Converting Wavelength to Frequency

Problem: What is the frequency of orange light at 600 nm?

Solution:

f = c / λ = (3 × 10⁸ m/s) / (600 × 10⁻⁹ m) = 5 × 10¹⁴ Hz = 500 THz

Example 2: Calculating Photon Energy

Problem: Calculate the energy of a blue photon (450 nm) in electron volts.

Solution:

E = hc / λ = (6.626 × 10⁻³⁴ J·s × 3 × 10⁸ m/s) / (450 × 10⁻⁹ m)

E = 4.42 × 10⁻¹⁹ J = 2.76 eV

Example 3: Color Temperature to Peak Wavelength

Problem: A light source has a color temperature of 4000K. What is its peak wavelength?

Solution:

λ_peak = 2,898,000 / T = 2,898,000 / 4000 = 724.5 nm (near-infrared, appearing warm white)

Example 4: Refraction in Glass

Problem: Blue light (450 nm) enters glass (n = 1.52). What is its wavelength in the glass?

Solution:

λ_glass = λ_vacuum / n = 450 / 1.52 = 296 nm

Note: The color perception remains blue because frequency (and thus photon energy) is unchanged.

Digital Color Representation

Digital systems represent colors using numerical values, but these don't correspond directly to wavelengths.

RGB Color Model

Computer displays use red, green, and blue channels, each with values from 0-255:

• Pure red: RGB(255, 0, 0)
• Pure green: RGB(0, 255, 0)
• Pure blue: RGB(0, 0, 255)
• White: RGB(255, 255, 255)
• Black: RGB(0, 0, 0)

Limitations of Digital Color

Digital displays cannot produce spectral colors directly. Instead, they create metameric matches by combining three primary wavelengths to simulate the appearance of other colors. The gamut (range of reproducible colors) is limited and doesn't include highly saturated spectral colors like pure yellow or cyan.

Wavelength to RGB Approximation

Converting a spectral wavelength to RGB requires algorithms that approximate human color perception. Simple linear interpolation doesn't work because the relationship between wavelength and perceived color is complex and non-linear.

Detailed Visible Light Spectrum Reference

The following comprehensive table provides detailed physical properties for specific wavelengths across the entire visible spectrum. For each wavelength, the table includes the perceived color, approximate hex color code for digital displays, frequency, photon energy in both electron volts and joules, and the momentum of a single photon. This reference is useful for physics calculations, optical engineering, and understanding the energetics of visible light.

The photon momentum values, while extremely small, are physically measurable and form the basis for radiation pressure. Solar sails, for example, exploit the cumulative momentum of billions of photons to propel spacecraft. The energy difference between violet (3.26 eV) and red (1.77 eV) photons is nearly a factor of two, which explains why shorter-wavelength photons are significantly more effective at driving photochemical reactions and why UV light causes sunburn while red light does not.

Common Light Sources and Their Characteristic Wavelengths

Different light sources emit at specific wavelengths determined by their physical mechanism of emission. The following detailed reference table covers lasers, LEDs, gas discharge lamps, and other sources commonly encountered in laboratories, industry, and everyday life.

The sodium D-line doublet at 589.0 nm and 589.6 nm has been one of the most important wavelengths in the history of optics. It serves as the standard wavelength for measuring refractive indices (the "D" in n_D), and the distinctive yellow-orange glow of sodium street lamps comes from this emission. The green laser pointer at 532 nm appears about 30 times brighter to the human eye than a red 650 nm laser of equal power, because 532 nm is very close to the peak sensitivity of human scotopic (low-light) vision.

Color Temperature Reference: From Candlelight to Blue Sky

Color temperature, measured in Kelvin, describes the color appearance of light emitted by a blackbody radiator at a given temperature. It is widely used in photography, cinematography, display calibration, and architectural lighting design. The following table provides a comprehensive reference from the warmest artificial sources to natural daylight conditions.

The peak wavelength column shows the wavelength at which the blackbody spectrum is brightest, calculated from Wien's displacement law. Note that at 2700 K, the peak is at 1073 nm (near-infrared), meaning most of the energy from incandescent bulbs is emitted as heat rather than visible light, explaining their poor energy efficiency of only 2-5%. LED and fluorescent sources are not true blackbodies; their "correlated color temperature" (CCT) describes which blackbody they most closely resemble in appearance.

The CRI (Color Rendering Index) column indicates how faithfully a light source reveals the colors of objects compared to an ideal reference. Incandescent and halogen sources achieve CRI 100 by definition, while LEDs range from about 80 to 97+ depending on quality. For critical color work in photography, art galleries, and retail, a CRI above 90 is recommended.

Summary

Understanding the relationship between visible light wavelengths and colors is fundamental to many fields:

• Visible spectrum: 380-700 nm, from violet to red
• Inverse relationship: Shorter wavelengths = higher frequency = higher energy
• Trichromatic vision: Three cone types (S, M, L) enable full color perception
• Spectral vs. non-spectral: Some colors (magenta, brown) require mixed wavelengths
• Color temperature: Describes light color based on blackbody radiation
• Applications: Displays, photography, medicine, agriculture, communications

Use our wavelength calculator to convert between wavelength, frequency, and energy for any visible or invisible light.

Frequently Asked Questions