Diffraction of Light at a Single Slit

Short answer

• When light passes through a single narrow slit, it does not simply form a bright image of the slit on a screen. It spreads out and produces a diffraction pattern: a broad, bright central maximum in the middle, flanked on both sides by dimmer secondary maxima separated by dark bands called minima. The dark minima appear at angles given by the formula a sin theta equals m lambda, where a is the slit width, lambda is the wavelength of the light, theta is the angle from the straight ahead direction, and m is a whole number 1, 2, 3, and so on. The central maximum is twice as wide as each secondary maximum, and the first secondary maximum carries only about 4.5 percent of the central maximum intensity. The pattern is one of the clearest demonstrations that light behaves as a wave, because rays alone cannot explain why light appears in places that straight line geometry says should be dark, or why darkness appears where light should fall.

What Diffraction Means

Diffraction is the spreading and bending of a wave when it passes through an opening or around the edge of an obstacle. It is a property of all waves, not only light. Sound waves entering a room through an open door can be heard by a listener standing in a part of the room that straight line rays could never reach. Ocean waves passing through a gap in a breakwater spread out across the sheltered water inside. In each case the wave does not keep to a narrow beam. It bends around the edges of the opening and fills in the space behind it.

Light does the same thing, but the effect is usually hard to notice in everyday life. The reason is scale. Diffraction becomes easy to observe when the opening is comparable in size to the wavelength of the wave passing through it. Sound has wavelengths of centimeters to meters, so ordinary doorways diffract sound plainly. Visible light has wavelengths of only about 390 to 770 nanometers, according to OpenStax University Physics Volume 3, so most everyday openings are far too wide to diffract light noticeably. A slit only a few times wider than the wavelength of light is a different matter. There the spreading becomes obvious, and the pattern it produces can be measured with simple equipment.

That measurement is the subject of this article. A single slit is the simplest aperture that shows the full diffraction pattern, and it is the starting point for understanding diffraction gratings, the resolution limits of telescopes and microscopes, and the way light behaves whenever it meets a small opening.

The Setup: One Slit, One Screen

The classic single slit experiment uses a small number of parts. A source of light of one color, called monochromatic light, shines through a narrow rectangular slit and onto a screen placed some distance away. A laser is the usual modern source because its light is nearly all one wavelength and its beam is narrow and steady. In a classroom version, a slide with a slit a fraction of a millimeter wide is placed in front of a laser pointer, and the pattern is projected onto a wall a few meters away.

Three quantities describe the setup. The slit width, written a, is the width of the opening. The wavelength, written with the Greek letter lambda, is the wavelength of the light. The distance from the slit to the screen, usually written D, sets how large the pattern appears. When the screen is far from the slit compared with the slit width, the rays heading toward any one point on the screen are nearly parallel, and the pattern takes the simple form described by the Fraunhofer diffraction formulas in this article. HyperPhysics notes that reasonable Fraunhofer results are obtained when the screen distance D is much larger than the slit width a, with the additional condition that D is much larger than a squared divided by lambda.

If white light is used instead of light of one color, each wavelength forms its own pattern at a slightly different scale, so the maxima smear into colored bands. That is why the cleanest demonstrations, and all the formulas in this article, use light of a single wavelength. The colored version is still instructive, and it is discussed later in this article, but it is not the pattern the minima formula describes.

What You See on the Screen

The pattern on the screen has a shape that surprises anyone who expects a simple bright bar. In the center there is a broad, bright band: the central maximum. On either side of it there are dark bands, the minima, where almost no light arrives. Between the dark bands there are fainter bright bands, the secondary maxima, which grow dimmer and narrower as they get farther from the center.

OpenStax describes the pattern in the same terms. The central maximum is larger than the maxima on either side, and the intensity decreases rapidly on either side. The side maxima are much less intense and not as wide as the central maximum. In the textbook diagram, the central maximum is drawn at only one sixth of its true height, because drawing it to scale would make the side maxima almost invisible. That single fact tells you how much of the light ends up in the middle of the pattern.

Three features of the pattern are worth fixing in mind before the explanation begins. First, the central maximum is the brightest part by a large margin. Second, the central maximum is twice as wide as any secondary maximum. Third, the dark minima are evenly spaced in a specific mathematical sense: their positions follow the formula a sin theta equals m lambda. Each of these features has a reason, and each reason follows from the wave nature of light.

Why the Pattern Forms: Huygens Wavelets

The explanation starts with a principle stated by the Dutch scientist Christiaan Huygens in the seventeenth century. Huygens principle says that every point on a wavefront acts as a source of secondary wavelets that spread out in all directions. When light reaches the slit, the wavefront inside the slit is a row of such sources, all starting in step with one another.

Straight ahead, toward the center of the screen, the wavelets from every part of the slit travel nearly the same distance. They arrive in step, crest matching crest, and they add together. That constructive addition is the bright central maximum. The center is bright for the simplest possible reason: nothing cancels there.

At an angle to one side, the story changes. Wavelets from different parts of the slit now travel different distances to reach the same point on the screen, so they arrive out of step. At some angles, the out of step arrival is complete enough that every wavelet finds a partner that cancels it exactly. The result is darkness: a minimum.

OpenStax explains the first minimum with a pairing argument that is easy to follow. Divide the slit mentally into two equal halves. Consider a wavelet from the top edge of the slit and a wavelet from the middle of the slit, which is the top edge of the lower half. At the angle of the first minimum, the wavelet from the bottom edge has traveled exactly one wavelength farther than the wavelet from the top edge. The wavelet from the middle has therefore traveled exactly half a wavelength farther than the one from the top, so the two arrive exactly out of step and cancel. The same pairing works for every other pair of points separated by half the slit width, one from the upper half and one from the lower half. Every wavelet is canceled by a partner, and the screen is dark at that angle. By symmetry, the same thing happens at the same angle on the other side.

The second minimum works the same way with four parts instead of two. Divide the slit into four equal quarters. At the angle of the second minimum, wavelets from corresponding points in neighboring quarters are half a wavelength out of step, and again every wavelet finds a canceling partner. The third minimum divides the slit into six parts, and so on. Each minimum corresponds to dividing the slit into an even number of equal parts and pairing them off so that everything cancels.

The secondary maxima sit between the minima, at angles where the cancellation is only partial. At those angles most wavelets still find canceling partners, but a small leftover group does not, and that leftover group produces a faint bright band. Because the leftover group gets smaller as the angle grows, the secondary maxima get dimmer farther from the center. That is why the pattern fades quickly on either side of the central maximum.

The Minima Formula, in Plain Language

The pairing argument leads directly to the central formula of single slit diffraction. The minima occur at angles theta that satisfy:

a sin theta equals m lambda, for m equals 1, 2, 3, and so on.

Each symbol has a plain meaning. The letter a is the slit width, the width of the opening the light passes through. The letter lambda is the wavelength of the light. The angle theta is measured from the straight ahead direction, the direction the light was traveling before it reached the slit. The number m is the order of the minimum: m equals 1 for the first minimum on either side of the center, m equals 2 for the second, and so on.

Note what m equals 0 would mean. Setting m to 0 gives theta equal to 0, the straight ahead direction, which is the center of the central maximum, not a minimum at all. That is why the minima formula starts at m equals 1. There is no zeroth minimum. The central maximum occupies the space between the first minimum on the left and the first minimum on the right.

The formula also explains the most useful qualitative fact about the pattern: a narrower slit makes a wider pattern. If a gets smaller, sin theta must get larger to keep a sin theta equal to m lambda, so the minima move to larger angles and the pattern spreads out. If a gets larger, the minima move to smaller angles and the pattern narrows. When the slit is much wider than the wavelength, the pattern collapses into a narrow bright bar that looks almost like the geometric image of the slit, which is why diffraction is invisible in ordinary wide openings. When the slit width approaches the wavelength itself, the first minimum moves toward 90 degrees and the central maximum fills the whole screen.

Wavelength matters in the opposite direction. Longer wavelengths, red light rather than violet light, produce larger angles for the same slit, so the pattern spreads wider. Shorter wavelengths produce a narrower pattern. This is why the pattern made by red light is visibly wider than the pattern made by blue or green light through the same slit.

Worked Example: Finding the Minima

A worked example makes the formula concrete. It uses the numbers from OpenStax University Physics Volume 3, Example 4.2, so that every step can be checked against that source. Light of wavelength 550 nanometers, which is green light in the middle of the visible range, passes through a slit of width 2.00 micrometers. A micrometer is one millionth of a meter, so 2.00 micrometers is 2.00 times 10 to the power of minus 6 meters, and 550 nanometers is 550 times 10 to the power of minus 9 meters.

For the first minimum, m equals 1. Rearranging the minima formula gives sin theta equals m lambda divided by a, which is 550 times 10 to the power of minus 9 meters divided by 2.00 times 10 to the power of minus 6 meters. That ratio is 0.275. The angle whose sine is 0.275 is about 16.0 degrees. So the first minimum sits 16.0 degrees to either side of the center.

For the second minimum, m equals 2. The sine of the angle is 2 times 550 nanometers divided by 2.00 micrometers, which is 0.550. The angle whose sine is 0.550 is about 33.4 degrees. The second minimum sits 33.4 degrees from the center on each side.

Two features of these numbers deserve attention. First, the central maximum extends 16.0 degrees on either side of the center, so its total angular width is about 32 degrees. Second, the gap between the first and second minima is 33.4 degrees minus 16.0 degrees, which is 17.4 degrees. The second maximum, which sits between those two minima, is therefore only about half as wide as the central maximum. That matches the general rule: the central maximum is twice as wide as each secondary maximum.

The same example can be run in reverse. OpenStax Example 4.1 gives visible light of wavelength 550 nanometers producing its second diffraction minimum at an angle of 45.0 degrees, and asks for the slit width. Rearranging the formula gives a equals m lambda divided by sin theta, which is 2 times 550 nanometers divided by sin 45.0 degrees. Sin 45.0 degrees is about 0.707, so the slit width is about 1.56 times 10 to the power of minus 6 meters, or 1.56 micrometers. The slit is only about three times wider than the wavelength of the light, which is exactly the regime where diffraction is strong. The first minimum for that slit sits at about 20.7 degrees, so the central maximum spans about 41 degrees in total.

How Wide Is the Central Maximum on a Screen

Angles are useful for theory, but in a laboratory the pattern is usually measured as distances on a screen. For small angles, the distance y from the center of the pattern to the mth minimum is approximately D times m lambda divided by a, where D is the distance from the slit to the screen. The width of the central maximum, the distance between the first minima on either side, is therefore approximately 2 D lambda divided by a.

A worked example shows the scale. Take green light of wavelength 550 nanometers, a slit of width 0.10 millimeters, and a screen 2.0 meters away. The distance from the center to the first minimum is D lambda divided by a, which is 2.0 meters times 550 times 10 to the power of minus 9 meters, divided by 0.10 times 10 to the power of minus 3 meters. That gives 0.011 meters, or 1.1 centimeters. The full width of the central maximum is twice that, 2.2 centimeters. The pattern is a few centimeters across on a screen two meters away: large enough to measure with a ruler, small enough to fit comfortably on a sheet of paper.

The same formula shows how each change affects the pattern. Doubling the screen distance doubles the width of the pattern. Halving the slit width doubles it as well. Switching from green light to red light, with a wavelength near 650 nanometers, widens it by about a fifth. These proportional changes are the reason the formula is worth remembering in words as well as symbols: the pattern grows with wavelength and screen distance, and shrinks with slit width.

The Intensity Pattern: Why the Sides Fade So Fast

The minima formula tells where the dark bands fall, but it does not say how bright the bright bands are. For that, the full intensity formula is needed. OpenStax gives the intensity at an angle theta as I equals I0 times the square of sin beta divided by beta, where beta equals pi times a sin theta divided by lambda, and I0 is the intensity at the center of the pattern. You do not need to evaluate that formula by hand to understand what it says. Its shape is what matters: a tall central peak, zeros at the minima, and rapidly shrinking bumps in between.

The numbers are striking. The first secondary maximum, the brightest of the side bands, has an intensity of only about 4.5 percent of the central maximum. The second secondary maximum has an intensity of only about 1.6 percent of the central maximum. OpenStax derives both figures from the phasor analysis: the first from a phase difference of about 3 pi radians, giving about 0.045 times I0, and the second from about 5 pi radians, giving about 0.016 times I0. After the second secondary maximum, the remaining bands are so faint that they are hard to see without a dark room and a sensitive detector.

This rapid falloff explains a common observation. In a classroom demonstration, most people see the bright central band and perhaps one faint band on each side, and they may miss the rest entirely. The pattern is genuinely there, but the light in the outer bands is a small fraction of the light in the center. Photographs of diffraction patterns often exaggerate the side bands by overexposing the central maximum, which is why textbook diagrams warn that the central peak is drawn much shorter than its true height.

The intensity formula also confirms the positions of the minima. The intensity is zero whenever sin beta is zero while beta is not zero, which happens when beta equals m pi for whole numbers m. Substituting the definition of beta gives pi times a sin theta divided by lambda equals m pi, which simplifies to the minima formula a sin theta equals m lambda. The two formulas agree, as they must, because they describe the same pattern.

What Changes the Pattern

Five changes cover almost everything that can happen to a single slit pattern. Each follows directly from the formulas above, and each can be checked by changing one thing at a time in a demonstration.

First, narrowing the slit widens the pattern. The minima move to larger angles, the central maximum grows broader, and the total light reaching the screen falls because less light gets through the narrower opening. Widening the slit does the opposite: the pattern narrows, brightens, and moves toward the simple geometric image of the slit.

Second, increasing the wavelength widens the pattern. Red light spreads more than violet light through the same slit. This is a direct consequence of the minima formula, where a larger lambda needs a larger sin theta for the same order m.

Third, moving the screen farther away enlarges the whole pattern in proportion to the distance. The angular positions of the minima do not change, because they depend only on the slit width and the wavelength, but the distances between features on the screen grow with D.

Fourth, using white light instead of light of one color replaces each sharp band with a smeared rainbow. Each wavelength forms its own pattern at its own scale, and the patterns overlap. The center stays white, because all wavelengths have their central maximum in the same place, straight ahead. Away from the center, the colors separate: violet, with the shortest wavelength, stays closest to the center, and red spreads farthest out. The dark minima of one color may be filled in by the bright maxima of another, so the colored pattern looks washed out compared with the crisp bands of laser light.

Fifth, changing the shape of the aperture changes the shape of the pattern. A circular aperture produces a bright central disk surrounded by faint rings, called the Airy disk, instead of the straight bands of a slit. A rectangular aperture produces a cross shaped pattern. The single slit is the simplest case, but the same wavelets and cancellation reasoning applies to every aperture shape.

Single Slit Versus Double Slit: Do Not Confuse Them

Single slit diffraction and double slit interference are related, and they are often taught in the same chapter, but they are different phenomena, and confusing them is the most common mistake students make with this topic. The distinction is worth stating plainly.

In single slit diffraction, the pattern comes from interference between wavelets originating in different parts of the same slit. There is one opening, and the light from one side of it interferes with the light from the other side. The result is a broad central maximum with rapidly fading side bands, and the minima follow a sin theta equals m lambda.

In double slit interference, the pattern comes from interference between light passing through two separate slits. The two slits act as two sources, and their light adds constructively or destructively depending on the path difference between the slits. The result is a set of evenly spaced, nearly equally bright fringes. The bright fringes of a double slit pattern are much more uniform in brightness than the side maxima of a single slit pattern, and they are much narrower relative to their spacing.

In practice, a real double slit experiment shows both effects at once. Each slit is itself narrow enough to diffract, so the single slit pattern acts as an envelope that limits how bright the double slit fringes can be at each angle. Fringes near the center of the envelope are bright, and fringes farther out are dimmer, following the single slit intensity curve. Some double slit fringes can even disappear entirely where they coincide with a single slit minimum. Understanding the single slit pattern is therefore a precondition for understanding the double slit pattern, but the two patterns are not the same thing, and their formulas describe different geometry: slit width in the single slit case, slit separation in the double slit case.

A related distinction matters for the vocabulary. Interference is the general name for waves adding together, constructively or destructively. Diffraction is what happens when waves spread after passing an aperture or around an obstacle. Single slit diffraction is interference happening inside one slit, but it is conventionally called diffraction because the spreading through the aperture is the phenomenon being studied. Keeping the two labels straight helps when reading textbooks, which sometimes use the words loosely.

Fraunhofer and Fresnel Diffraction

The formulas in this article describe Fraunhofer diffraction, the pattern observed when the screen is far from the slit. Fraunhofer diffraction is the far field case: the wavefronts arriving at the screen are effectively plane waves, and the pattern depends only on angle, not on the exact distance to the screen beyond the overall scale. The conditions are that the screen distance D is much larger than the slit width a, and also much larger than a squared divided by lambda. In most classroom demonstrations both conditions are easily met.

When the screen is close to the slit, the pattern is described by Fresnel diffraction instead. The Fresnel pattern is more complicated: the wavefronts are still curved when they reach the screen, the pattern changes shape as the screen moves, and the simple minima formula does not apply directly. Fresnel diffraction is important in optics design and in near field imaging, but it is a separate topic from the far field pattern covered here. If a demonstration produces a pattern that does not match the minima formula, the first thing to check is whether the screen is far enough away for the Fraunhofer conditions to hold.

Where Single Slit Diffraction Matters

Single slit diffraction is not only a classroom demonstration. It sets a limit on how sharply any optical instrument can form an image. Every lens, mirror, and aperture diffracts the light passing through it, so the image of a point of light is never a perfect point. It is a small diffraction pattern, and two points that are too close together blur into one. This is the diffraction limit, and it is why larger telescopes can resolve finer detail than smaller ones: a larger aperture produces a narrower diffraction pattern. The same limit applies to microscopes, cameras, and the human eye. The single slit is the simplest geometry that shows the effect, and the circular aperture version of the same reasoning gives the Airy disk and the Rayleigh criterion used to quote the resolving power of real instruments.

Diffraction also matters in measurement. Because the pattern depends on wavelength and slit width in a known way, it can be run in reverse: measure the pattern, and infer the wavelength of the light or the width of the slit. Spectrometers use diffraction gratings, which are many slit systems, to separate light by wavelength and identify the composition of stars, lamps, and laboratory samples. The single slit version of the same idea is used in teaching laboratories to measure the wavelength of a laser or the width of a narrow opening from the pattern it produces.

Everyday life offers a glimpse of the effect without any equipment. Hold two fingers close together in front of a bright light and look through the narrow gap between them, and a pattern of light and dark lines appears, running parallel to the fingers. The gap between the fingers is acting as a slit, and the lines are the diffraction pattern. The same effect produces the colored fringes sometimes seen around a bright street light on a foggy night, where tiny water droplets act as small apertures. These are not laboratory curiosities. They are the same physics, visible wherever light meets an opening close to its own wavelength in size.

The effect also explains something about the design of optical instruments. A camera stopped down to a very small aperture gains depth of field, but if the aperture becomes too small, diffraction begins to soften the image. Photographers call this diffraction limited imaging. There is a trade off between the sharpness gained by a small aperture and the softness imposed by diffraction, and the best aperture for a given lens sits between the two extremes. The single slit pattern is the reason the trade off exists at all.

Common Misconceptions

Several misunderstandings recur whenever this topic is taught, and each is worth correcting directly.

The first is the idea that the dark minima are places where no light reaches the screen. Light does reach those points. Wavelets from different parts of the slit arrive there, but they arrive out of step and cancel. Darkness in a diffraction pattern is not an absence of light. It is light canceling light. This is the same point that makes interference surprising in general: adding more light to a place can make it darker.

The second is the idea that the secondary maxima are as bright as the central maximum, or nearly so. They are not. The first is about 4.5 percent as intense, and the rest are dimmer still. Diagrams that draw the side bands at similar heights to the central peak are misleading, and they are usually drawn that way only so that the side bands can be seen at all.

The third is the idea that a wider slit makes a wider pattern. It is the reverse. A wider slit makes a narrower pattern, and a narrower slit makes a wider pattern. The inverse relationship is one of the most reliable facts in wave physics, and it is also one of the least intuitive. It follows from the minima formula, and it can be checked in seconds by changing the slit width in a demonstration.

The fourth is the confusion between single slit and double slit patterns described above. If a pattern has evenly spaced fringes of nearly equal brightness, it is a double slit interference pattern, possibly modified by a single slit envelope. If it has one dominant central band with rapidly fading side bands, it is a single slit diffraction pattern. The shape of the pattern identifies the geometry that made it.

The fifth is the idea that diffraction proves light is a wave and nothing else. Diffraction proves that light behaves as a wave in this experiment, and it was historically one of the decisive pieces of evidence for the wave theory of light. Light also shows particle like behavior in other experiments, such as the photoelectric effect, and modern physics describes light as having both wave and particle aspects. The single slit pattern establishes the wave aspect. It does not settle the whole nature of light on its own.

Seeing It Yourself

The finger gap demonstration described above is the simplest way to see single slit diffraction without equipment. Hold your index and middle fingers close together, leaving a gap of a fraction of a millimeter, and look through the gap at a bright, small light source such as a distant street light or a bare bulb. Dark and bright lines appear across the gap. Widening or narrowing the gap changes the spacing of the lines, showing the inverse relationship between slit width and pattern width in real time.

A laser pointer and a slit slide give a cleaner result. Shine the laser through the slit onto a wall a few meters away in a darkened room, and the central maximum and the first secondary maxima appear clearly. Measure the distance from the center to the first minimum and the distance from the slit to the wall, and the minima formula gives the slit width if the wavelength is known, or the wavelength if the slit width is known. This is a standard school and university laboratory exercise, and the numbers come out close to the nominal values when the measurements are made carefully.

Two safety notes apply. Never look directly into a laser beam, and never point a laser at anyone eyes. The pattern should always be viewed on a screen or a wall, never by looking back along the beam. Second, the finger gap demonstration should use a distant light, not the Sun. Never look at the Sun through a narrow gap or any other aperture.

Why the Pattern Convinced Physicists

The single slit pattern mattered historically because it is hard to explain without waves. If light traveled only in straight rays, a narrow slit would produce a narrow bright bar on the screen, with darkness everywhere else. Instead, light appears in the region that ray geometry says should be dark, and darkness appears inside the region that ray geometry says should be bright. No arrangement of straight rays can produce that. Waves, which spread and interfere, produce it naturally.

The same reasoning applies to the light around us every day. When you hear sound around a corner, you are experiencing diffraction. When you see light spread after passing a narrow gap, you are experiencing the same phenomenon at a much smaller scale. The single slit experiment isolates that phenomenon in its cleanest form, with one opening, one wavelength, and one screen, so that the pattern can be predicted exactly and checked against measurement. That combination of a simple prediction and a measurable result is why the experiment remains a standard part of physics teaching, and why the minima formula is worth learning rather than merely memorizing.

For readers who want to place this topic in the wider picture of light, our guide to what the electromagnetic spectrum is explains where visible light sits among radio waves, infrared, ultraviolet, and X rays, and how wavelength determines the behavior of each band. The bending of light at a boundary between materials is a different effect with its own rules, covered in our guide to what refraction is. Diffraction, refraction, and interference are distinct phenomena, and telling them apart is the key to reading any optics textbook with confidence.

Frequently Asked Questions

What is diffraction of light at a single slit?

Diffraction of light at a single slit is the spreading of light into a pattern of bright and dark bands when it passes through one narrow opening. The pattern has a broad, bright central maximum, dark minima on either side, and dimmer secondary maxima between the minima. It happens because wavelets from different parts of the slit interfere with one another, adding together in some directions and canceling in others.

What is the formula for single slit diffraction minima?

The minima occur where a sin theta equals m lambda, with m equal to 1, 2, 3, and so on. Here a is the slit width, lambda is the wavelength of the light, theta is the angle from the straight ahead direction, and m is the order of the minimum. The first minimum on each side has m equal to 1, the second has m equal to 2, and the central maximum lies between the two first minima.

Why is the central maximum twice as wide as the secondary maxima?

The central maximum stretches from the first minimum on one side to the first minimum on the other side, a total angular span of about 2 lambda divided by a for small angles. Each secondary maximum sits between two neighboring minima, which are about lambda divided by a apart in angle. The central maximum therefore covers twice the angular width of any secondary maximum.

Why does a narrower slit produce a wider diffraction pattern?

The minima formula requires a sin theta to equal m lambda. If the slit width a gets smaller, sin theta must get larger to keep the product the same, so the minima move to larger angles and the pattern spreads out. This inverse relationship is a general property of waves: confining a wave to a narrower space makes it spread more widely afterward.

What is the difference between single slit diffraction and double slit interference?

Single slit diffraction comes from interference between wavelets from different parts of the same slit, and it produces one broad central maximum with rapidly fading side bands. Double slit interference comes from interference between light passing through two separate slits, and it produces evenly spaced fringes of nearly equal brightness. A real double slit pattern shows both effects, with the single slit pattern acting as an envelope that dims the fringes farther from the center.

Does white light produce a single slit diffraction pattern?

White light produces a diffraction pattern, but it is not the clean set of sharp bands that light of one color produces. Each wavelength forms its own pattern at its own scale, so the bands overlap and smear into colors. The center stays white because all wavelengths have their central maximum straight ahead, while the colors separate away from the center, with violet closest in and red farthest out.

Sources & references

• OpenStax, University Physics Volume 3, Section 4.1, Single-Slit Diffraction. Read 5 November 2026. https://openstax.org/books/university-physics-volume-3/pages/4-1-single-slit-diffraction
• OpenStax, University Physics Volume 3, Section 4.2, Intensity in Single-Slit Diffraction. Read 5 November 2026. https://openstax.org/books/university-physics-volume-3/pages/4-2-intensity-in-single-slit-diffraction
• HyperPhysics, Georgia State University, Fraunhofer Diffraction. Read 5 November 2026. https://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/fraungeo.html
• HyperPhysics, Georgia State University, Circular Aperture Diffraction. Read 5 November 2026. https://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/cirapp2.html
• NASA Science, Visible Light. Read 5 November 2026. https://science.nasa.gov/ems/09_visiblelight/