Learn how to Create Light Rays and Dust Particles Using a Custom Brush in Photoshop.

How to Create Light Rays and Dust Particles Using a Custom Brush in Photoshop

A beam of light through a window looks even better with visible dust floating in the air and streaks of light catching that dust, even when neither came through straight out of camera. This tutorial builds a custom brush specifically designed to scatter believably, then uses that same brush for both floating dust particles and motion-blurred light rays.

Why the Default Brush Scattering Falls Short

Photoshop’s built-in Scattering option ties how far particles spread to the brush’s own size, which keeps a small brush’s particles clustered too close together to look like real floating dust.

1. Try Painting Dust With a Regular Brush

   Select a regular round brush and try painting a few dots to represent dust particles.

2. Turn On Shape Dynamics and Scattering

   Go to Window > Brush to open the Brush panel, raise Size Jitter under Shape Dynamics, and raise the Scattering value.

3. Notice the Particles Stay Too Close Together

   Notice that even with scattering turned up, particles from a small brush only spread within a small area, since scattering distance is tied to brush size.

Building and Testing a Custom Brush Canvas

A brush built from a small document with two dots, one large and visible and one tiny and far away, tricks Photoshop into treating the whole canvas as the brush size while only showing one small dot.

4. Create a New 500 by 500 Pixel Document

   Press Cmd/Ctrl+N and create a new document at 500 by 500 pixels.

5. Paint a Dot in One Corner

   Choose a regular round brush and paint a black dot in the bottom right corner of the canvas.

6. Paint a Tiny Dot in the Opposite Corner

   Switch to a much smaller brush and paint a tiny dot in the top left corner of the canvas.

7. Define the Brush Preset

   Go to Edit > Define Brush Preset and name the new brush.

8. Shrink the Brush Size to Hide the Extra Dot

   Switch to the working document, select the new brush, and shrink its size down until only the corner dot remains visible.

Why a Second, Distant Tiny Dot Makes the Trick Work

Because Photoshop treats the entire 500 by 500 canvas as the brush’s true size, scattering spreads particles across that full area rather than a tiny, cramped one. Shrinking the brush down afterward keeps the visible dot small while preserving that same large underlying scatter radius, which is exactly what makes the particles spread out convincingly.

Maximizing Randomness in the Brush Settings

Pushing Shape Dynamics and Scattering to their extremes on this new brush produces particles that no longer look like an obviously repeated stamp.

9. Raise Size Jitter and Lower Minimum Diameter

   Under Shape Dynamics, raise Size Jitter and lower the minimum diameter so particle sizes vary widely.

10. Raise Angle Jitter

    Raise Angle Jitter as well so each particle’s rotation also varies randomly.

11. Increase and Break Up Scattering

    Click on Scattering, raise the amount significantly, and turn on Both Axes so particles spread widely in every direction rather than along a single line.

Painting Multiple Dust Layers at Different Scales

Painting the same custom brush across several separate layers, at different sizes and opacities, builds up dust that reads as naturally varied rather than uniform.

12. Paint a Layer of Dust

    Create a new layer and paint dust across it with the custom scatter brush.

13. Change the Layer to Soft Light

    Change that layer’s blend mode from Normal to Soft Light so the dust blends into the image’s existing light and color.

14. Lower the Opacity

    Reduce the layer’s opacity so the dust reads as subtle rather than overwhelming.

15. Repeat With Different Brush Sizes

    Create additional new layers, adjusting the brush size larger or smaller each time, and change each new layer to Soft Light as well.

Why Multiple Layers at Different Opacities Look More Convincing

Real floating dust naturally varies in size, brightness, and density depending on distance and lighting, which a single flat layer of identical particles can’t capture. Building up several separate layers, each at a different particle size and opacity, recreates that same natural variation instead of one obviously uniform effect.

Sampling Color From the Image for the Dust

Sampling a light color directly from the photo, rather than using plain white, keeps the dust particles’ color consistent with the rest of the scene.

16. Sample a Light Color From the Photo

    Press B for the Brush tool, hold Option/Alt, and sample a light color already present in the image.

17. Paint Larger Particles With That Color

    Increase the brush size and paint a new layer of larger dust particles using that sampled color.

Creating Light Ray Streaks With Motion Blur

The exact same custom brush, painted near a light source and stretched with Motion Blur, can double as the streaked light rays cutting through the dust.

18. Adjust the Brush Settings for Larger Particles

    Lower the Scattering amount slightly and increase the brush size to create larger particles near the light source.

19. Paint Near the Light Source

    Paint a new layer of these larger particles in the area right around the light source, such as near a window.

20. Apply Motion Blur

    Go to Filter > Blur > Motion Blur, choose an angle that matches the direction of the light, and set a distance for the streak length.

Building Up the Streak Effect With the Repeat Filter

Pressing the repeat filter shortcut reapplies the same Motion Blur settings instantly, making it fast to build up progressively stronger light streaks.

21. Paint Another Small Amount of Particles

    Paint a bit more of the particle brush in the same area near the light source.

22. Reapply the Same Blur With a Shortcut

    Press Cmd/Ctrl+F to reapply the exact same Motion Blur settings again without reopening the dialogue.

23. Repeat and Change to Soft Light

    Repeat painting and reapplying the blur across a few layers as needed, then change each of those layers to Soft Light as well.

Why Repeating the Same Filter Beats Reopening the Dialogue

Reopening the Motion Blur dialogue every time risks accidentally choosing a slightly different angle or distance than before, which would make the streaks look inconsistent with each other. The repeat filter shortcut reapplies the identical settings instantly, keeping every additional pass of blur perfectly consistent with the last.

Saving the Custom Brush for Reuse

Saving the final brush settings as a new preset keeps this exact scatter brush available for future images without rebuilding it from scratch.

24. Open the Brush Preset Menu

    Press B for the Brush tool, right-click, and click the gear icon in the panel that appears.

25. Choose New Brush Preset

    Choose New Brush Preset, rather than Save Brushes, since Save Brushes exports the entire brush set instead of just this one.

26. Name and Save the Brush

    Name the new preset something identifiable, such as Scatter Dust, and save it.

Masking the Light Flare Layers Where Unwanted

Grouping the light ray layers and adding a mask keeps the streaked light contained to where it actually makes sense in the frame.

27. Group the Light Ray Layers

    Shift-click the light ray layers and press Cmd/Ctrl+G to group them together.

28. Add a Layer Mask to the Group

    Add a layer mask to the group and paint black with a regular brush around any edges where the effect shouldn’t appear.

29. Group Everything Together

    Group the dust and light ray effects together as a final step, once both are finished.

Why This Approach Works

Building the custom brush from an oversized canvas with a distant second dot is what solves the built-in scattering limitation, giving particles a much larger area to spread across than the brush’s visible size would normally allow. Using layered opacity and varied particle sizes across several passes, rather than one single layer, is what makes the dust read as naturally varied instead of obviously repeated. Reusing the exact same brush for both dust and motion-blurred light rays is what ties the whole atmospheric effect together as one consistent look.

Final Thoughts

A custom brush built once this way keeps paying off on every future image that could use a little floating atmosphere or a beam of light catching visible dust. Saved as a preset, the same brush and blur combination is ready to drop into any photo with a strong light source, no rebuilding required.

Quick Reference: Keys, Menus and Settings

• Brush panelWindow > Brush: Shape Dynamics and Scattering
• Make the brushCmd/Ctrl + N, 500 x 500 px; dot bottom right, tiny dot top left; Edit > Define Brush Preset
• RandomizeSize Jitter all the way up, Minimum Diameter down, Angle Jitter up, Scattering up
• Dust layersSoft Light, lower Opacity; B + Alt/Option-click to sample a light color
• Light raysFilter > Blur > Motion Blur, Angle to match the light; Cmd/Ctrl + F repeats it
• Save the brushB, right-click, gear icon > New Brush Preset
• Contain the raysCmd/Ctrl + G, mask the group, paint black

No AI, no generative credits.