Gobo lighting: what a gobo is and how to make one in Blender

What is a gobo?

A gobo is a stencil or template placed inside or in front of a light source to control the shape of the light it emits and of the shadow it casts. In a theatre fixture, the gobo sits in the gate, at the point of focus between the lamp and the lenses, usually in an ellipsoidal reflector spotlight or a moving head. Sitting in the focal plane is what gives the projection its crisp, sharp-edged pattern. Studio photographers use the word more loosely, for any device that casts a shadow, such as a black panel set between a light and the subject.

Stage gobos come in three materials. Steel gobos are the sturdiest, but the design often needs small bridges added to display correctly, and those bridges can show in the projected image. Glass gobos are clear glass with a partial mirror coating that blocks the light: they need no bridges, carry more intricate images and color, and give the best image fidelity, at the price of being the most fragile. Plastic gobos, used in LED ellipsoidal spotlights, can be full color as well.

Where the word comes from

According to Wikipedia, "gobo" started as a shortening of "go between" in Thomas Edison's phonograph recording process. Some of the people who worked on those recordings also worked in the Edison film studio, where they put patterns between the new electric lights and the scenery, and the word moved to lighting because the pattern "goes between" the light and the scenery. It seems to have become standard in cinema studios in the 1930s. Readings of the word as an acronym, such as "goes before optics", are recent.

Gobo, cookie or flag

A stencil placed after the optics no longer gives a finely focused image, and the more precise names for it are flag or cucoloris, "cookie" for short. Cookies are used farther from the fixture than gobos and generally give softer edges. The distinction carries over to Blender: a cut-out card in front of a light behaves like a cookie, while an image inside the light itself is closer to a true gobo.

What gobo lighting is used for

On stage and at events, gobo lighting covers a wide range of jobs:

• Breakup: a pattern of leaves on a stage floor, or light that seems to come through a leafy canopy. Breaking up the light from a man-made source gives a more natural look.
• Logos and text: a company logo projected on a wall, a couple's names at a wedding, artwork at a corporate event.
• Moving patterns: automated fixtures in nightclubs and music venues throw moving shapes; simpler setups project stars or leaves onto a ceiling.
• Architecture: gobos also serve in architectural lighting.

In CG, the usual suspects are the shadow of a window frame across a floor, leaves breaking up a wall, and any pattern that keeps a large, even light from looking flat. You could model the window or the tree that would cast the shadow, but it often sits outside the frame, and a gobo lets you place the pattern exactly where the shot needs it without moving the set. The guide to lighting in Blender covers the light types this builds on. Blender settings below are checked against the Blender 5.2 manual.

Method 1: a gobo card between the light and the scene

This method works in Cycles and in EEVEE, with a Spot or an Area light.

1. Set up the light. Add a Spot light and aim it at the area to pattern. In Object Data Properties > Light > Beam Shape, open the Angle until the cone covers the area, and tick Show Cone to see it in the viewport.
2. Add the card. Add a plane between the light and the scene and scale it so it fills the whole cone: any part of the cone that misses the card lets unshaped light through.
3. Build the material. Add an Image Texture with the stencil and plug its Alpha output into the Factor of a Mix Shader, with a Transparent BSDF in the first Shader socket and a dark Diffuse BSDF in the second. A Factor of 0 picks the first shader, so the transparent parts of the image become holes. The Principled BSDF's Alpha input does the same job in one node; the manual notes it is usually linked to the Alpha output of an Image Texture. If the stencil is a black-and-white image with no alpha channel, plug its Color output into the Factor instead, swap the two shaders so white lets light through, and set the image's Color Space to Non-Color.
4. Hide the card. In Object Properties > Visibility > Ray Visibility, untick Camera, and in Cycles Glossy as well, so the card shows neither in the frame nor in reflections. Leave Shadow ticked: it is the option that lets the object cast shadows, so it is what draws the pattern.

How Cycles treats the card

The Transparent BSDF passes light straight through the surface as if there were no geometry, and the manual calls it useful with alpha maps. Its Color input is the probability, for each wavelength, that light passes straight through, so feeding it a colored image tints the light that goes through the holes: the CG version of a glass gobo. Only pure white is completely transparent, so make sure the open parts of the stencil really reach white. If you stack several cards in front of one light, keep an eye on Render Properties > Light Paths > Max Bounces > Transparent, the maximum number of transparency bounces.

How EEVEE treats the card

In Material Properties > Settings, keep Transparent Shadows ticked. The manual describes it as transparent shadows for a material that contains a Transparent BSDF, and says turning it off renders faster but does not give accurate shadows, which for a gobo means losing the point of the card. With the Dithered render method, shadows behave like the former Alpha Hashed mode. If the stencil has soft or noisy edges, the manual's alpha clip setup, a Math node set to Greater Than on the alpha, snaps it to 0 or 1.

The detail of the pattern then depends on the shadow maps. In Object Data Properties > Light > Shadow, Resolution Limit is the minimum size of a shadow map pixel, so a lower value keeps a fine stencil readable at the cost of memory. Filter blurs shadow aliasing, and Jitter increases shadow precision with a high performance cost, since the shadow map can no longer be cached.

Method 2: a textured Spot light (Cycles only)

In Cycles, a light can be fully defined with shader nodes, and an Image Texture in its node tree projects a picture with no card in the scene. It is the closer match to a theatre gobo, since the pattern comes from the light itself, and there is nothing to hide from the camera or from reflections.

1. Select the Spot light and open a Shader Editor: it shows the light's nodes, by default an Emission shader connected to a Light Output. The same tree appears in Object Data Properties > Nodes. There is no Use Nodes switch to tick: in Blender 5.2 a light always uses its nodes.
2. Add a Texture Coordinate, a Mapping and an Image Texture node. Connect Normal to the Mapping node's Vector, then the Mapping output to the Image Texture's Vector. The manual states that the Normal output can be used on Point and Spot lights and takes the rotation of the light into account, so the pattern turns with the light.
3. Connect the image's Color to the Emission Color for a colored slide, or to its Strength for a black-and-white stencil, with the image in Non-Color.
4. Set the Image Texture's Extension to Clip. Outside the 0 to 1 range of the image, pixels become transparent black instead of repeating the picture across the cone.
5. Center and size the pattern with the Mapping node's Location and Scale. The Normal output is a direction, whose X and Y run from -1 to 1, while the image only covers 0 to 1, so expect to shift and scale it before it sits in the middle of the cone.

The light's Power, color, Angle and Blend still apply, because the basic light settings are applied on top of the Light Output node. Two limits matter. Only Emission-based shading contributes to lighting, so a BSDF in a light's tree has no effect. And EEVEE ignores light node trees altogether: its limitations page states that lights can only have one color, so a textured light renders as a plain spot there.

Light settings that change the projection

Distance matters as much as size. Wikipedia's articles on gobos and cookies give the rule from both ends: the closer the gobo is to the subject, the sharper the shadow, and the closer it is to the light, the softer and less defined. A card in Blender behaves the same way once the light has a size, so a crisp window pattern wants a small light, a card near the lit surface, or both. In EEVEE, the manual also lists a smaller light shape among the fixes for light leaking in soft shadows.

Visible beams: gobo projection through a volume

On stage, the pattern on the floor is only half the effect: in haze, the beam shows too, and each opening in the gobo becomes its own shaft. In Blender the light needs something to scatter in. The Volume Scatter shader lets light scatter as it passes through the volume, and the manual names fog as its typical use. Density sets how much of the light interacts with the volume. Anisotropy sets the direction: 0 scatters evenly, positive values mostly forward, negative values mostly backward. The volumetric lighting guide walks through the setup.

Put the volume on an object surrounding the scene, or just the beam, rather than in the world. The manual warns that with a world volume shader, the world surface shader and sun lights have no effect, which takes an HDRI out of the lighting. In Cycles, volume bounces are zero by default, which gives single scattering. EEVEE supports single scattering only and ignores light node trees, so if the beam has to work in EEVEE, the card is the only one of the two methods available; volume quality is set in Render Properties > Volumes, where Resolution and Steps trade video memory for quality.

Render time and noise

The direct pattern is the easy part for Cycles: shadow rays aim at the light and pass through the card, and the manual points out that the Transparent BSDF lets shadows find light sources straight through surfaces. The cost sits around it.

• Bounce light from bright patches. The manual's page on reducing noise says very bright spots are mostly a problem for indirect lighting. Clamping only indirect light, in Render Properties > Light Paths > Clamping > Indirect Light, trims fireflies and leaves what the camera sees directly untouched; set too low, it loses highlights.
• Volumes. Unbiased rendering of scattering can be noisy, so a hazy gobo shot needs more samples than the same shot in clean air. Raising the Step Rate in Render Properties > Volumes shortens the render at the cost of volume detail.
• EEVEE. Light Jitter has a high performance impact, Volumetric Shadows in Render Properties > Sampling > Shadows is very computationally expensive, and turning Transparent Shadows off is faster but loses the pattern's accuracy.

Extra samples add up over an animation. Once a hazy test frame gives you its minutes per frame, the render time calculator turns that figure and the frame count into a total.

Common mistakes

• The pattern is blurry. The light is too large for the distance: lower the Spot light's Radius, or the Area light's Size and Spread, or move the card toward the lit surface. Lowering Blend will not help, since it only acts on the cone's edge. In EEVEE, also check the Filter and Resolution Limit of the light's shadow.
• The card shows in the render. It is still visible to camera or glossy rays, or in EEVEE it is captured by light probes: untick Light Probes > Sphere and Plane in Object Properties > Visibility. Unticking Shadow instead removes the pattern along with the card.
• The card darkens the other lights. It blocks every light, not only the gobo light. On each of the other lights, Object Properties > Shading > Shadow Linking can exclude it from the blockers, though shadow linking can make renders slower.
• Wrong color space. A stencil read as sRGB goes through a color conversion its gray levels should not get. The manual says stencil maps should never have a color conversion applied, so set them to Non-Color; keep sRGB for a colored slide.
• A glass gobo made with a Glass BSDF. Light focused through refractive glass is a caustic, a well-known source of fireflies, and with caustics turned off, glass shadows may come out too dark. A Transparent BSDF fed with a colored image tints the light without refraction; the caustics guide covers the cases where you do want refraction.
• The textured light does nothing. Either the scene renders in EEVEE, which ignores light node trees, or the tree uses a BSDF, which has no effect on a light. Only Emission counts.
• The pattern repeats across the cone. The Image Texture's Extension is still on Repeat; set it to Clip.