Updated 25 September 2026
To ensure lighting consistency, you must explicitly define the primary light source’s position and intensity in every prompt and use a reference image to lock that geometry in place. This approach prevents the AI from randomly repositioning shadows between frames, creating a cohesive visual narrative that feels intentional rather than accidental.
Lighting is not merely about brightness; it is about geometry. When you generate multiple images for a storyboard, each iteration is essentially a new calculation by the model. Without strict constraints, the model often chooses the most aesthetically pleasing lighting for each individual frame, which usually means front-facing, flat illumination. This breaks continuity. To fix this, you must treat lighting as a fixed architectural element rather than a decorative choice. You are building a stage, not painting a portrait. The following methods help you impose that discipline on the generation process.
Defining a Fixed Light Source in Your Initial Prompt
The most common mistake is describing lighting qualitatively ("bright," "warm," "soft") without specifying spatial relationships. Qualitative terms are subjective and vary significantly between generations. Instead, you must use directional vectors and spatial anchors. Start every prompt by establishing the horizon and the primary light angle relative to the subject.
Use clear, directional language. Phrases like "light coming from the upper left at a forty-five-degree angle" provide a coordinate system that the model can interpret more reliably than "nice lighting." If your subject is facing forward, specify if the light is frontal, side-lit, or back-lit. Decide on one dominant direction and repeat this exact phrase in every prompt for the sequence. Consistency in wording leads to consistency in output.
Consider the environment as a container for light. If the scene is outdoors, specify the time of day relative to the sun's position, such as "mid-morning sun from the east." If indoors, describe the window placement relative to the camera view. For example, "large window on the left side of the frame casting shadows to the right." By tying the light to physical objects in the scene, you create a logical constraint that the model is less likely to violate. Avoid abstract adjectives. Do not say "beautiful light." Say "hard directional light from the north-west." The more geometric your description, the more stable the result.
Using Reference Images to Anchor Lighting Geometry
Text descriptions alone are often insufficient for complex lighting scenarios because they rely on the model’s internal interpretation of words. Reference images provide concrete visual data that anchors the lighting geometry. When you upload a reference image, you are telling the model to mimic not just the style, but the physical behavior of light within that specific scene setup.
Select a reference image that has simple, clear lighting cues. Avoid images with multiple competing light sources unless your scene requires them. A single-source setup is easier to replicate across frames. When using a reference, instruct the model to match the shadow direction and intensity. Some interfaces allow you to weight the reference image higher than the text prompt. Do this. Let the visual geometry dominate the textual description.
If you are generating a sequence of different angles for the same subject, keep the reference image consistent. Do not change the reference between shots unless you intend to change the lighting setup. This creates a visual anchor. The model uses the reference to understand how shadows fall on objects of different shapes. For instance, if the reference shows a sharp shadow from a sphere, the model learns to apply similar sharpness to other objects in subsequent generations. This reduces the "drift" that occurs when relying solely on text. Ensure your reference image has high contrast, as this makes the light direction unmistakable to the algorithm.
The Role of 'Key Light' and 'Fill Light' Terminology in Prompts
Professional lighting terminology provides a shorthand for complex setups. Using terms like "key light," "fill light," and "rim light" helps the model understand the hierarchy of illumination. The key light is the primary source that defines the shape and direction of shadows. The fill light softens those shadows without changing their direction. The rim light separates the subject from the background.
In your prompts, specify which light is dominant. For example, "strong key light from the left, minimal fill light from the right." This tells the model exactly how much contrast to expect. If you omit the fill light description, the model might default to high-contrast noir lighting, which may not match your previous frames. By explicitly stating the relationship between key and fill, you control the contrast ratio.
Use these terms consistently. If you start with a "soft key light," continue to use that descriptor. Switching between "soft," "diffused," and "gentle" can yield slightly different results. Standardize your vocabulary. Create a small glossary for your project and stick to it. This reduces variability. Additionally, specify the color temperature if relevant. "Warm key light" versus "cool key light" can drastically change the mood and perceived time of day. Keep this consistent across the sequence to maintain atmospheric continuity.
Checking for Shadow Consistency Across Frames
After generating your images, you must audit them for continuity. Do not assume consistency; verify it. Open your images side-by-side and look only at the shadows. Ignore the colors and details for a moment. Focus on the direction and hardness of the shadows. Are they falling in the same direction? Do they have similar edge softness?
If shadows drift, adjust your prompt to reinforce the direction. For example, if the shadow moved slightly to the center, add "strictly side-lit" to the next prompt. Check for color shifts as well. Sometimes the model changes the white balance between frames, making one look warmer than the other. This can break immersion. Adjust your color temperature descriptors if needed.
Look at the highlights. Highlights should appear on the same side of the subject in every frame. If the highlight moves, the light source has moved. Correct this immediately. It is easier to fix early in the sequence than to regenerate the entire set later. Keep a log of successful prompts. Note which combinations of directional words produced the most stable results. This builds a reliable toolkit for future projects.
Workflow: Generating a Base Lighting Setup Before Adding Details
Do not attempt to generate a fully detailed image from scratch. Start with a minimalist approach. Generate a base image with simple shapes and clear lighting. Focus only on establishing the light direction and shadow behavior. Use simple geometry: spheres, cubes, cylinders. These shapes reveal lighting flaws clearly.
Once you have a base image with the correct lighting geometry, use it as the foundation. Generate subsequent shots by adding details to this established light setup. Keep the lighting prompt identical while expanding the subject matter. This layered approach separates the technical aspect of lighting from the creative aspect of composition. It reduces the cognitive load on the model.
Iterate on the base until it is perfect. Then, use that base as the reference for all subsequent frames. This ensures that every shot inherits the same lighting logic. You are building a system, not just generating images. The system provides stability. The details are added on top of this stable foundation. This method is slower initially but saves time in post-processing and ensures a professional result.
This guide is most useful for designers and illustrators who need predictable, repeatable results for storyboards and sequential art. It assumes you are comfortable with basic prompt engineering and value consistency over artistic surprise. If you prefer spontaneous, one-off artistic expressions where each image stands alone, this rigid methodology may feel restrictive, and you might find more value in guides focused on abstract style mixing.