Light isn’t a single color or a single “thing.” It’s a spread of electromagnetic waves with different wavelengths and frequencies. When people ask, “what is spectrum of light,” they’re really asking how that spread is organized and how we make sense of it. In plain terms, the spectrum of light is the way we describe light’s energy distributed across wavelengths. Separate those wavelengths and you’ll see distinct colors in the part our eyes can detect—what we call the visible light spectrum.

In this guide, we’ll define the light spectrum, show how white light splits into its component colors, place visible light within the broader electromagnetic spectrum, outline the major regions from gamma rays to radio waves, clarify the order of visible colors with approximate wavelength ranges, explain the three classical types of spectra (continuous, emission, absorption), and cover how spectra are measured in practice—wavelengths in nanometers and spectral distribution plots you’ll encounter in labs and engineering work. We’ll close with a brief look at why all of this matters across science and technology.

What Is the Spectrum of Light

Definition of the Light Spectrum

The spectrum of light is the distribution of electromagnetic radiation as a function of wavelength or frequency. In other words, it tells you how much light energy is present at each wavelength. Within the segment our eyes can sense—the visible band—each wavelength corresponds to a perceived color. Encyclopedic references define “spectrum” this way and place visible light as a narrow band within the broader continuum of electromagnetic radiation. For an authoritative overview, see the succinct definition in Britannica’s entry on the spectrum in physics and its overview of light as electromagnetic radiation.

Put simply: the light spectrum is the “fingerprint” of light’s energy across wavelengths. Show that fingerprint as a graph and you’ll see peaks, valleys, and sometimes narrow lines—clues to what produced the light and what it passed through.

How Light Can Be Separated Into a Spectrum

White light contains many wavelengths. When it passes through a prism, those wavelengths bend by slightly different amounts because the refractive index of glass depends on wavelength (a phenomenon called dispersion). Shorter wavelengths (violet/blue) bend more than longer wavelengths (red), so the beam spreads into a rainbow. Newton’s classic experiments in the 1660s demonstrated this clearly: he dispersed sunlight with a prism and then recombined the colors to show they were already present in the light, not created by the glass. A clear, accessible treatment of dispersion and prism behavior appears in Physics LibreTexts on dispersion and prisms/25:_Geometric_Optics/25.05:Dispersion-_Rainbows_and_Prisms).

Prisms aren’t the only tools. Diffraction gratings—tiny, evenly spaced lines—also separate wavelengths, producing spectra with high resolution that scientists use in spectrometers. Whether you use a prism or a grating, the idea is the same: different wavelengths take different paths and land in different places, so you can “see” the spectrum.

The Electromagnetic Spectrum Explained

What Is the Electromagnetic Spectrum

All light is electromagnetic radiation. The electromagnetic spectrum is the full range of these waves, from extremely short wavelengths (gamma rays) to extremely long ones (radio waves). Wavelength and frequency are inversely related through the speed of light, so as wavelength gets shorter, frequency and photon energy go up. That’s why violet light (shorter wavelengths) carries more energy per photon than red light (longer wavelengths). For a compact tour across the bands with visuals and ranges, see NASA’s educational pages on the electromagnetic spectrum and university texts like Physics LibreTexts on the EM spectrum/16:_Electromagnetic_Waves/16.06:_The_Electromagnetic_Spectrum).

Major Categories of the Electromagnetic Spectrum

Engineers and scientists usually refer to these broad regions (boundaries are approximate and can vary slightly by source):

• Gamma rays: very short wavelengths, typically shorter than about 0.01 nm.
• X-rays: roughly 0.01–10 nm.
• Ultraviolet (UV): approximately 10–400 nm.
• Visible light: about 400–700 nm (detailed just below).
• Infrared (IR): about 700 nm–1 mm.
• Microwaves: roughly 1 mm–1 m.
• Radio waves: about 1 mm up to many kilometers.

The important intuition is simple: moving from gamma to radio, wavelengths increase while frequencies and photon energies decrease. These ranges are summarized consistently in resources like NASA’s Tour of the Electromagnetic Spectrum and Physics LibreTexts/16:_Electromagnetic_Waves/16.06:_The_Electromagnetic_Spectrum).

The Visible Light Spectrum

Wavelength Range of Visible Light

The visible light spectrum is the slice of the electromagnetic spectrum detectable by the human eye. It’s commonly standardized to about 400–700 nanometers (nm). Some sources cite slightly wider limits, such as 380–750 nm, because the eye’s sensitivity fades gradually at the edges and varies among individuals. For a concise overview of this range and its perceptual context, see Britannica’s explanation of the visible spectrum and NASA’s page on visible light.

A nanometer is one-billionth of a meter. That unit matches the scale where human vision and common spectrometers operate, which is why you’ll see visible wavelengths reported in nm across engineering documents and lab software.

Colors Within the Visible Light Spectrum

Within the visible band, the colors follow a consistent order from shorter to longer wavelengths:

• Violet: roughly 380–450 nm
• Blue: about 450–495 nm
• Green: about 495–570 nm
• Yellow: about 570–590 nm
• Orange: about 590–620 nm
• Red: about 620–750 nm

Keep in mind these boundaries are approximate. Real-world sources usually aren’t “pure” single wavelengths—they’re blends. But the order is dependable: shorter wavelengths look violet/blue; longer wavelengths look orange/red.

If you want to compare how different spectrum combinations perform in real growing environments, see our guide on red blue vs white grow lights.

For growers evaluating stem elongation, flowering response, or crop morphology control, our far-red LED grow light guide explains how far-red can be used in commercial production.

Different Light Spectrums Explained

Practitioners often encounter three canonical patterns when looking at spectra. Because many searchers use the phrase “different light spectrums,” we’ll use that wording here once, then return to the standard plural, spectra.

Continuous Spectrum

A continuous spectrum includes all wavelengths within a range without gaps. Hot, dense objects tend to emit such broadband light. Sunlight arriving at Earth’s surface, once you remove atmospheric effects, is a good example: it shows a smooth distribution across the visible and into the infrared. Incandescent filaments are another everyday source with a nearly continuous output. Authoritative explainers on continuous spectra, such as entries in Britannica on electromagnetic radiation, discuss how dense matter produces these smooth distributions.

What you see on a plot: a gently varying curve that rises and falls across wavelengths. Superimposed features may appear if the light passes through gases or filters.

Emission Spectrum

An emission spectrum from a low-density gas shows bright, narrow lines at specific wavelengths. Those lines correspond to electron transitions in atoms or molecules. Because each element has unique allowed transitions, its emission lines form a distinctive “barcode.” A classic laboratory reference is hydrogen’s Balmer series in the visible; the prominent H-alpha line appears near 656.28 nm, as tabulated by NIST’s hydrogen line data. Neon signs are another intuitive example: the striking orange-red glow arises from strong emission lines of neon in the orange/red part of the spectrum. University texts like Physics LibreTexts on spectral lines/05:_Radiation_and_Spectra/5.05:_Formation_of_Spectral_Lines) explain how these lines form and why their wavelengths are element-specific.

What you see on a plot: a dark baseline with sharp, bright spikes at particular wavelengths—like a city skyline at night.

Absorption Spectrum

An absorption spectrum occurs when broadband light passes through a cooler gas or absorbing medium that removes specific wavelengths. The result is a continuous background with narrow dark lines—“missing” light—at those absorbed wavelengths. The solar spectrum famously shows thousands of such lines, called Fraunhofer lines, which helped scientists identify elements in the Sun’s atmosphere by matching line positions to laboratory data. For background and significance, see Britannica’s article on Fraunhofer lines.

What you see on a plot: a smooth curve crossed by narrow dips at precise wavelengths—like a ribbon with carefully snipped notches.

How Light Spectrum Is Measured

Wavelength and Nanometers

Spectra are commonly labeled in wavelength (λ), measured in nanometers for the visible range. One nanometer equals one-billionth of a meter (10⁻⁹ m). Using nm keeps numbers in a convenient range (hundreds rather than fractions of micrometers) and aligns with instrument displays and standards. It also makes it easy to relate bands to color perception—for instance, a noted line near 656 nm (H-alpha) falls in the red.

If you prefer frequency, you’ll see units of hertz (Hz). Engineers switch between wavelength and frequency depending on the problem, but for visible light, wavelength in nm is the most common reporting format in spectroscopy, photometry, and colorimetry.

Spectral Distribution

Engineers often visualize spectra using a spectral power distribution (SPD) plot. An SPD shows how much radiant power (absolute or relative) a source emits at each wavelength. It’s the go-to way to characterize a light source in the lab and in many standards documents. The International Commission on Illumination (CIE) defines SPD precisely and provides standard illuminants with published SPDs that underpin colorimetric calculations; see the CIE’s terminology entry for SPD and spectroradiometric measurement guidance.

How to read a basic SPD:

• Broadband vs. line features: A smooth, continuous shape suggests a thermal-like or phosphor-broadened source; narrow spikes indicate line emissions from gases or specific emitters.
• Peaks and valleys: A strong peak around ~450 nm is common in blue-pumped sources; a broad hump spanning green to red can indicate converted emissions. In contrast, a solar-like SPD appears as a smooth continuum with narrow absorption dips (Fraunhofer lines) overlaid.
• Resolution matters: The apparent sharpness of lines depends on instrument resolution and sampling. Higher-resolution spectrometers show narrower, deeper features. If lines look unusually wide or shallow, consider the instrument’s bandwidth and any smoothing used.

What SPDs are used for: color rendering studies, matching to standard illuminants, comparing source characteristics, and linking spectral content to downstream optical effects. For formal definitions and measurement guidance, the CIE documents above are a solid starting point.

Why Understanding the Spectrum of Light Matters

Mastering spectra lets you interpret what light reveals about sources and materials—and design better measurements and systems. A few high-level examples:

• Astronomy and astrophysics: Spectral lines identify elements in stars and galaxies and enable measurements such as redshift. The history of Fraunhofer lines is a foundational example of how absorption patterns unlock composition and conditions in stellar atmospheres.
• Physics and optics: Dispersion, interference, and material optical properties all play out across wavelength. Understanding spectra guides lens and filter choices, coating design, and instrument alignment.
• Medical imaging and diagnostics: X-rays and parts of the ultraviolet/infrared bands support imaging and therapeutic techniques. Knowing where these lie on the electromagnetic spectrum helps set expectations for penetration and detector design.
• Telecommunications and sensing: Microwaves and radio waves occupy longer-wavelength regions with engineering uses from antennas to radar. The wavelength–frequency relationship informs everything from waveguides to propagation models.
• Optical research and metrology: Spectral measurements—especially SPDs—underpin colorimetry, standard illuminants, and characterization of sources and materials in labs and production testing.

Here’s the deal: a spectrum is both a map and a story. It shows where energy sits and hints at how that energy was made or modified. Once you can read the map, you can ask better questions and make better design choices.

Further Reading

• For a concise encyclopedic treatment of visible light and where it sits in the broader electromagnetic spectrum, see Britannica’s explanation of the visible spectrum and its broader discussion of the electromagnetic spectrum.
• For an approachable, diagram-rich tour of each band from gamma rays to radio, explore NASA’s educational pages on the electromagnetic spectrum.
• For a textbook-style walkthrough of dispersion, spectra formation, and band ranges, consult Physics LibreTexts’ modules on the electromagnetic spectrum/16:_Electromagnetic_Waves/16.06:_The_Electromagnetic_Spectrum) and on dispersion and prisms/25:_Geometric_Optics/25.05:Dispersion-_Rainbows_and_Prisms).
• Optional, application-focused reading on lighting: FY LIGHTING Systems’ guide to grow light spectrum (note: this resource is focused on a specific application area and is separate from the general primer above): https://www.fytechsystems.com/grow-light-spectrum-ultimate-guide/

Continue Learning About Vertical Farm

To understand how light spectrum affects fixture selection, crop planning, and vertical farm lighting design, read our full vertical LED grow lights guide for commercial vertical farming.

If you are unsure whether ultraviolet light should be included in your lighting strategy, read our article on .UVB in grow lights

For projects that require flexible light recipes across different crop stages, learn more about adjustable spectrum LED grow lights with multi-channel control.