Beam Angle
Definition, Function, and Choosing the Right Beam for Marine Lighting
Plain-English Definition
A beam angle is the width of a light’s output pattern, measured in degrees. It defines how far and wide light spreads from a fixture.
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Narrow beam (10–30°) focuses light into a tight cone for long-distance visibility.
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Wide beam (60–120°) spreads light over a broad area for general coverage.
In simple terms, beam angle determines whether a light is designed for reach or coverage.
Why Beam Angle Matters on a Boat
Beam angle directly affects how light performs in marine settings:
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Narrow beam: Great for spotlighting, forward-facing searchlights, or highlighting specific features like flags or tower tops.
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Medium beam: Ideal for deck or cockpit lighting where you want brightness without harsh glare.
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Wide beam: Best for flood lighting, underwater illumination, or general area coverage around docks and transoms.
Choosing the right beam angle ensures visibility, safety, and energy efficiency while minimizing glare for you and nearby vessels.
How to Measure Beam Angle
Beam angle is the angle between points on either side of the light beam where intensity drops to 50% of the peak brightness.
For example:
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A 20° beam concentrates light into a tight spotlight.
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A 90° beam spreads light broadly with softer edges.
Applications by Beam Type
| Beam Type | Typical Angle | Ideal For | Example Use |
|---|---|---|---|
| Spot Beam | 10–30° | Distance and precision | Searchlights, masthead lights |
| Flood Beam | 40–90° | Wide coverage | Deck, engine room, underwater lights |
| Diffuse Beam | 100°+ | Ambient illumination | Cabins, courtesy lighting |
Choosing the Best Beam Angle
When selecting marine LED lights, consider:
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Purpose: Navigation, deck lighting, underwater display, or cabin ambience
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Mounting height and distance: Higher mounts benefit from wider beams
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Surface color: Light reflects differently on white gelcoat vs. dark hulls
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Brightness (lumens): A narrow beam will appear brighter even with fewer lumens
For underwater or dock lighting, pairing wide-angle LEDs with high-lumen output provides the best coverage and visual effect.
DRSA-Recommended Lighting Examples
Lumitec SeaBlazeX2 Underwater Light – 90° Beam
Balanced spread ideal for transom coverage with deep-water penetration.
DRSA Pacific G4 Engine Room Light – 120° Beam
Ultra-wide pattern for full utility lighting inside tight spaces.
OceanLED X8 Colours – Dual Beam System
Combines focused projection with wide peripheral light for maximum visual impact.
Quick Reference
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Narrow beam: Long distance, focused light
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Wide beam: Short distance, broader coverage
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Measured in degrees (°): The higher the number, the wider the light spread
Example in a Sentence
“The captain switched to a wide 90-degree beam angle to illuminate the entire swim platform while docking at night.”
Related Marine Lighting Terms
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Lumens – The total light output or brightness
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Candela – The measure of light intensity in a single direction
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Color Temperature – Determines the warmth or coolness of light color
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IP Rating – Indicates waterproofing and dust resistance
Shop Related Categories
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Marine LED Flood Lights
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Underwater Dock & Transom Lights
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Engine Room & Utility Lighting
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Navigation & Deck Illumination