Whether you draw technical illustrations or expressive artwork in Adobe Illustrator, the influence of light and shade play a role in how you depict your subject matter. Along with applying blends, gradients and meshes to add dimensionality and realism, you can use the program's effects and blending modes to simulate the impact of bright light sources illuminating your work. Instead of building these effects directly into object fills, start with a basic geometric shape that models the beam from a searchlight, flashlight or lamp.
Draw an object above your artwork, either on the same or a different layer. Placing this object on its own layer gives you greater flexibility in how you adjust and review your work. Use the Pen tool to create a freeform shape, or the Rectangle or Ellipse tools to draw a geometric object.
Set the fill color of the object to 255, 255, 255 in an RGB document or 0, 0, 0, 0 in a CMYK file. Use the Color or Control panel, or the foreground swatch in the Tools panel, to assign color. Alternatively, set the "Color" panel to "HSB" mode and set "B," for brightness, to 100 percent. Set the stroke color to "None."
Press "Shift-Ctrl-F10" to open the "Transparency" panel if it isn't already visible. Set the object's blending mode to "Overlay" for a bright light or "Soft Light" for a dimmer appearance. To reduce the influence of the object, lower its opacity to 55 percent.
Open the "Effect" menu's "Blur" submenu and choose "Gaussian Blur." Increase the blur radius until the edges of the object soften enough to create the illusion of distance between the light source and the objects it illuminates. The greater the distance between the light and the object, the softer the edges of the light beam.
Unlike Adobe Photoshop, Adobe Illustrator assigns blending modes to objects, not to document layers. Unless you explicitly assign appearance properties to an object, it does not take on any of the characteristics of other objects assigned to the same layer.
Select your light object and create a Graphic Style to pass its properties on to the style preset so you can apply the same appearance to other objects with a single click.
The Flare tool creates a prefabricated lens flare that adds the illusion of light interacting with camera optics. Apply the tool directly on your artboard or double-click the tool in the Tools panel to view the Flare Tool Options dialog box, in which you can size and adjust the center, halo, rays and rings of the flare effect, and omit either or both the rays and rings. The Flare tool's output combines transparency and blending modes to create its effect. Open the "Object" menu and choose "Expand" to access the individual objects within a flare and examine their properties.
Blur effects rely on pixels to create their soft edges. Open the "Effect" menu and choose "Document Raster Effects Settings" to adjust the resolution at which Adobe Illustrator creates these effects. Make the resolution consistent with how you intend to use your work: 72 pixels per inch for Web graphics or 300 ppi for print production. Otherwise, your file may look superb in the application and as an onscreen graphic, but appear pixelated when you print it.
The impact of effect settings varies depending on the size of your artwork and the viewing percentage at which you examine your work.
Information in this article applies to Adobe Illustrator CC 2014, Adobe Illustrator CC and Adobe Illustrator CS6. It may differ slightly or significantly with other versions or products.