This guide teaches you how to make light hurt enemies in Unreal Engine 4 using dynamic lighting and blueprint scripting. You’ll learn to detect light exposure, apply damage over time, and customize effects for immersive gameplay.
Key Takeaways
- Use dynamic lights: Static lights won’t trigger events, so use movable or stationary lights with movable components.
- Leverage blueprint scripting: Create logic to detect when an enemy is in light and apply damage over time.
- Implement line traces: Use line traces to check if light reaches the enemy without obstructions.
- Add visual feedback: Include particle effects, sound cues, and screen flashes to enhance the experience.
- Optimize performance: Use timers and efficient checks to avoid performance drops in large scenes.
- Test thoroughly: Adjust light intensity, damage rate, and detection range for balanced gameplay.
- Customize for different enemies: Apply varying damage levels or effects based on enemy type or resistance.
Introduction: Why Light Should Hurt Enemies
Imagine a stealth horror game where sunlight burns vampires, or a sci-fi shooter where UV beams fry alien creatures. Making light hurt enemies in Unreal Engine 4 adds a layer of strategy and immersion. It’s not just about visuals—it’s about gameplay mechanics that respond to the environment.
In this guide, you’ll learn how to make light hurt enemies in Unreal Engine 4 using a combination of lighting, blueprint scripting, and collision detection. Whether you’re building a survival game, a puzzle platformer, or a narrative-driven experience, this system can elevate your design.
We’ll walk through setting up dynamic lights, detecting when enemies are exposed, applying damage over time, and adding visual feedback. By the end, you’ll have a fully functional system you can expand and customize.
Step 1: Setting Up Your Project
Visual guide about How to Make Light Hurt Enemies Unreal Engine 4
Image source: numerama.com
Before diving into logic, make sure your project is ready.
Create a New Project
Open Unreal Engine 4 and create a new Blueprint project. Choose the “Third Person” template for simplicity, or start with a blank project if you prefer. Enable “Starter Content” to access basic materials and meshes.
Set Up the Level
Place a few basic meshes like cubes or spheres to act as your enemies. You can also import character models later. Add a directional light (like the sun) and a few point lights around the level. These will be your light sources.
Enable Movable Lights
Static lights bake into lightmaps and can’t trigger events. To make light hurt enemies, you need dynamic lighting. Select your lights and in the Details panel, set Mobility to “Movable.” This allows them to interact with gameplay systems.
Create an Enemy Blueprint
Right-click in the Content Browser, go to Blueprint Class, and choose “Character” or “Pawn.” Name it “BP_Enemy.” This will be your base enemy that reacts to light.
Open BP_Enemy and add a Capsule Component for collision. You can also add a Skeletal Mesh if you have one. For now, a simple shape works.
Step 2: Detecting Light Exposure
Now we need to detect when an enemy is in light. We’ll use a combination of line traces and light intensity checks.
Understanding Light Detection
Unreal Engine doesn’t have a built-in “is in light” function. So we simulate it. The idea: from the enemy’s position, shoot a line toward the light source. If the line reaches the light without hitting anything, the enemy is exposed.
Add a Line Trace in Blueprint
Open BP_Enemy and go to the Event Graph. Right-click and add an Event Tick node. This runs every frame.
From Event Tick, drag out and add a Line Trace By Channel node. Set the Trace Channel to “Visibility” or create a custom one.
Set the Start to the enemy’s location. You can get this with Get Actor Location.
Set the End to the light’s location. You’ll need a reference to the light actor. One way is to use a Tag or Actor Reference variable.
Get Light Location
To get the light’s location, you can use a Get All Actors Of Class node. Search for “PointLight” or “DirectionalLight.” Then use a For Each Loop to check each light.
Alternatively, assign a Tag like “LightSource” to your lights. Then use Get All Actors With Tag and loop through them.
Check for Obstructions
The Line Trace will return a Hit result. If Hit Actor is not the light itself, something is blocking the light (like a wall). Only if the trace hits the light or nothing at all is the enemy exposed.
Use a Branch node: if the trace hits the light (or nothing), proceed. Otherwise, skip.
Check Light Intensity
Even if the trace reaches the light, it might be too dim to hurt. Use Get Light Brightness or Get Intensity on the light component.
Compare it to a threshold (e.g., 500). Only apply damage if brightness is above that.
Step 3: Applying Damage Over Time
Once we detect light exposure, we need to hurt the enemy.
Create a Damage Timer
In BP_Enemy, add a Timer Handle variable. Use Set Timer by Function Name to call a custom function every 0.5 seconds (or your preferred interval).
Name the function “CheckLightDamage.”
Implement the Damage Function
Create a new function called CheckLightDamage. Inside, repeat the line trace and brightness check from earlier.
If the enemy is in bright light, apply damage.
Use the Take Damage node. Set the damage amount (e.g., 10) and damage type (create a custom one if needed).
Track Health
Add a Float variable called “Health” and set default to 100.
In the Take Damage event, subtract the damage from Health.
Add a Branch: if Health <= 0, destroy the enemy or play a death animation.
Prevent Constant Damage
To avoid spamming damage every frame, use a boolean flag like “IsInLight.” Only apply damage when the state changes from not in light to in light.
Or, use the timer to apply damage at intervals, not every tick.
Step 4: Enhancing with Visual and Audio Feedback
Gameplay feels better with feedback. Let’s add effects.
Add Particle Effects
When the enemy is hurt by light, spawn a particle system. Use a Niagara or Cascade effect like sparks, smoke, or glowing cracks.
In the CheckLightDamage function, after applying damage, use Spawn Emitter at Location.
Place it at the enemy’s location or on specific bones if using a skeleton.
Play Sound Cues
Add a Sound Cue that plays when damage is applied. Use Play Sound at Location.
Choose a sizzle, scream, or energy zap sound. Adjust volume and attenuation.
Screen Flash (Optional)
For first-person games, add a brief screen flash when the player uses a light weapon.
Use a Post Process Material with a white overlay. Trigger it via Blueprint when light hits an enemy.
Light Flicker Effect
Make the light flicker when it hits an enemy. In the light’s blueprint, use a Timeline to vary intensity.
Or, use a Material Parameter Collection to control brightness globally.
Step 5: Optimizing Performance
Checking every enemy every frame can be costly. Let’s optimize.
Use Timers Instead of Tick
Avoid heavy logic in Event Tick. Use timers with longer intervals (e.g., 0.3–0.5 seconds).
This reduces CPU load, especially with many enemies.
Limit Light Checks
Only check lights within a certain radius. Use Get All Actors Within Distance.
Or, assign lights to a specific layer and check only those.
Disable Checks When Not Needed
If an enemy is dead or far from any light, stop the timer.
Use a boolean like “ShouldCheckLight” to control the timer.
Use Event-Driven Updates
Instead of constant checks, trigger updates when the enemy moves or the light changes.
Use On Actor Begin Overlap and End Overlap with light volumes (see next section).
Step 6: Using Light Volumes (Alternative Method)
Another approach is to use invisible volumes that detect when enemies enter lit areas.
Create a Light Volume
Add a Box Collision component to an empty actor. Name it “LightVolume.”
Set it to overlap only with Pawns or your enemy class.
Detect Overlap
In the LightVolume blueprint, use On Actor Begin Overlap and End Overlap.
When an enemy enters, start a timer to apply damage.
When it exits, stop the timer.
Link to Light Source
Attach the volume to a light actor. Or, place it manually where light should hurt.
This method is simpler but less precise than line traces.
Combine Both Methods
Use volumes for broad detection and line traces for accuracy.
For example, only run line traces when the enemy is inside a light volume.
Step 7: Customizing for Different Enemies
Not all enemies should react the same way.
Create Enemy Subclasses
Make child blueprints of BP_Enemy: BP_Vampire, BP_Alien, BP_Robot.
Each can have different health, damage resistance, or reactions.
Adjust Damage Based on Type
In the damage function, check the enemy class.
Use a Switch on Class node to apply different damage amounts.
Or, use a Float variable “LightResistance” and multiply damage by (1 – Resistance).
Add Unique Effects
Vampires could turn to dust. Aliens might mutate. Robots could short-circuit.
Use different particle effects, sounds, and animations.
Implement Weaknesses and Immunities
Some enemies might be immune to certain lights (e.g., UV vs. infrared).
Use an Enum to define light types and check compatibility.
Step 8: Testing and Debugging
Now test your system thoroughly.
Test in Different Lighting Conditions
Move enemies in and out of light. Check if damage applies correctly.
Use different light intensities and colors.
Debug with Print Strings
Add Print String nodes to show health, light status, and trace results.
This helps identify issues quickly.
Check for False Positives
Ensure enemies aren’t damaged when behind walls or in shadows.
Adjust line trace length and channel settings.
Profile Performance
Use the Stat Unit command in the console to check CPU and GPU usage.
If performance drops, reduce timer frequency or limit active checks.
Troubleshooting Common Issues
Even with careful setup, problems can arise.
Light Doesn’t Hurt Enemies
Check: Is the light Movable? Are line traces hitting the light? Is the timer running?
Ensure the enemy blueprint has the correct logic and variables.
Damage Applies Too Fast or Too Slow
Adjust the timer interval and damage amount.
Use a Float variable for damage per second and calculate accordingly.
Performance Issues with Many Enemies
Reduce check frequency. Use spatial partitioning or disable distant enemies.
Consider using C++ for heavy logic if blueprints lag.
Line Traces Hit Wrong Objects
Set the correct Trace Channel. Use “Visibility” or create a custom one.
Exclude certain objects from the trace using collision settings.
Effects Don’t Play
Verify particle systems and sounds are properly referenced.
Check if the spawn location is valid and not inside geometry.
Conclusion: Light Up Your Game Design
Making light hurt enemies in Unreal Engine 4 opens up creative possibilities. You’ve learned to detect light exposure using line traces, apply damage over time with blueprints, and enhance the experience with effects and feedback.
This system isn’t just for horror games. Think about puzzles where players must shine light to weaken foes, or stealth sections where avoiding beams is key. The mechanics are versatile and scalable.
Remember to test often, optimize for performance, and customize for your game’s needs. With these tools, you can turn something as simple as light into a powerful gameplay element.
Now go create something brilliant—and make those enemies fear the sun.