Illuminating a 25' W x 10' D choral riser requires precise photometric planning. This technical case study demonstrates a dual 45-degree frontal lighting strategy at a 20ft mounting height to achieve a uniform 50+ foot-candle (f.c.) intensity. By applying the Inverse Square Law and 3D cross-lighting, we optimize Color Rendering Index (CRI) and eliminate facial shadows, meeting the rigorous standards for both live performance and 4K video capture.
1. The Challenge: Engineering Light for a 25ft Choral Riser
This church lighting project was approached with a focus on photometric precision. The goal was to provide a professional-grade environment for a community choral group.
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Target Area: A choral riser system measuring 25 ft wide by 10 ft deep.
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Elevation: Tiered seating rising from floor level to 4 ft high.
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Constraints: High 20ft ceiling; truss mounting only; no high-center lighting position available.
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The Benchmark: Maintain a minimum horizontal illuminance of 50 foot-candles (f.c.) across all tiers to ensure performers can read complex sheet music without eye strain.
2. Technical Calculation: From Lumens to Foot-Candles
To guarantee 50 f.c. At the target, we must account for the Inverse-Square Law and the Cosine Effect of the 45-degree angle.
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Vertical Height: 20 ft.
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Diagonal Throw Distance (d): At a 45-degree vertical angle, d = √(20² + 20²) ≈ 28.3ft
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Required Luminous Intensity ($I$): Using the formula E = (I × cosθ) / d², to achieve E = 50 f.c. , the source must output approximately 55,000 Candelas.
The Layout Strategy: Rather than relying on a single source, we implemented a symmetrical 45-degree cross-lighting technique.
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Horizontal Positioning: Fixtures are placed 45° off-center to provide three-dimensional depth.
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Vertical Angle: The 20ft height creates the ideal 45° downward angle, reaching the back row (4ft elevation) while minimizing direct glare for the front row.
3. Recommended Equipment: Precision Over Power
For church applications, "brightness" is secondary to "accuracy." We selected fixtures that balance high CRI with professional-grade optics.
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Primary Wash (The Workhorse):
KP2 18*15W Ultra Thin LED Par Light RGBW 4 in 1
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Performance: Capable of delivering 60,000+ Candela within a 25° beam angle.
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Uniformity: By utilizing four units in a cross-configuration, the beam overlap ensures that the illuminance variance across the 25ft width remains within ±10% .
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Frontal Floor Fill:
KBL1 200W COB Bi-color LED Audience Blinder
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The "Shadow Killer": Two low-intensity fixtures placed at floor level to fill chin and eye-socket shadows often missed by high-angle truss lighting.
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4. Engineering Insights: Beyond the Lumens
From a technical perspective, transitioning to high-efficiency LED systems offers two major advantages:
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Total Connected Load: Six 200W fixtures draw only 1.2 kW—less than 10% of a standard 20A church lighting circuit capacity.
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Flicker-Free Dimming: This is critical for the church’s digital ministry, ensuring 4K video recording remains clear and artifact-free at any dimming level.
5. FAQ
Q: What does 50 foot-candles (f.c.) mean for a stage?
A: 50 f.c. is equivalent to the illumination of a high-end drafting room. It is the professional standard for choral groups to ensure music readability and clear facial expressions for HD cameras.
Q: How many lights are needed for a 25ft wide choir?
A: For a 20ft mounting height, we recommend a 4-to-6 fixture configuration. Four high-output LED PARs provide the primary 45° wash, while two floor-level units eliminate lower-facial shadows.
Q: Why use a 45-degree angle for church lighting?
A: The 45° angle is the "Golden Rule" of stage lighting. It mimics natural sunlight, providing the most flattering facial features while preventing harsh glare from affecting the performers' vision.