Lighting Calculations

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# Lighting Calculations - PowerPoint PPT Presentation

Chapter 20. Lighting Calculations. Lighting Calculations . Lumen Method – determines average light levels in large open areas Point Calculations – determines light levels at a specific point on an object or surface. Lumen Method Calculations.

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Presentation Transcript
Chapter 20

### Lighting Calculations

Lighting Calculations
• Lumen Method – determines average light levels in large open areas
• Point Calculations – determines light levels at a specific point on an object or surface
Lumen Method Calculations
• 1 foot candle (FC) = 1 Lumen (Lms) divided by 1 square foot (area / A)
• 1 FC = 1 LM ÷ A
• Illuminance (E) (amount of light falling onto an object measured in foot candles) = Lumens divided by Area (in sq. ft.)
• E = Lms ÷ A (sq. ft.)
Lumen Method Example 1Solving for Illuminance(E) Level
• Room 10’ x 15’
• 5 down lights
• 1000 Lumens each down light
• E = Lms ÷ A
• Illuminance = Lumens divided by Area
• A = 10’ x 15’ = 150 sq. ft.
• 1000 Lumens x 5 down lights = 5000 lumens
• E = 5000 Lms ÷ 150 sq. ft.
• E = 37.5 Lms per sq. ft.
• E = 37.% foot candles (FC)
• Room 10’ x 15’ (A = 150 sq. ft.)
• Illuminance level (E) = 60 foot-candles
• Need Lumens / Luminaires
• E = Lms ÷ A - original equation
• Lumens needed = Illuminance x Area
• Lms = E x A
• Lms = 60 E x 150 sq. ft.
• Lms = 9000 Lumens
• Lumens needed = Illuminance x Area
• Lms = E x A
• Lms = 60 E x 150 sq. ft.
• Lms = 9000 Lumens
• 550 lumens = per luminaire
• Luminaires needed = Lumens needed divided by Lumens per luminaire
• Luminaires (X) = 9000 (lumens) ÷ 550 Lumens per Luminaire
• 9000 ÷ 550 = 16.36
• Always round up with any point.
• Luminaires needed = 17
Lumen Method Safety Factors
• Light loss factor (LLF) – light loss due to deteriorating lamps
• Industry standard of .85 for a light loss factor
• Coefficient of Utilization (CU) – effectiveness of luminaires working on surfaces of the space to deliver light to the target surface.
• Direct fixture or downlight – CU = 85% (0.85)
• Indirect fixture – CU = 50% (0.50)
• Spot or Accent – CU = 95 (0.95)
• Wash or ambient – CU = 75% (0.75)
Lumen Method Calculations with Safety Factors
• Illuminance = Lumens ÷ Area
• Illuminance = (Lumens x LLF x CU) ÷ Area
• Lumens needed = Illuminance target x Area
• Lumens needed = (Illuminance target x Area) ÷ (LLF x CU)
The Point Calculation Method
• Estimate location of lighting equipment
• Light density = Candle power = Candela
• Candela information given by Manufacturer
• Center Bean Candle Power – CBCP – center of a directional light
• Illuminance = Candela value ÷ Distance (squared)(in feet)
• E = CD ÷ D2
Point Calculation Example 1
• 10’-0” ceiling
• Accent Fixture
• Above a plate on a table 3; above the finished floor (A.F.F.)
• Illuminance = Candela value ÷ Distance2
• E = CD ÷ D2
• CD = 10,000 Candelas
• D2 = 7 ft 2 = 49 square feet (units get squared too)
• E = 10,000 CD ÷ 49 sq.ft.
• E = 204 Foot-candles
Point Calculation Example 2
• 10’-0” ceiling
• Accent Fixture
• Above a plate on a table 3; above the finished floor (A.F.F.)
• Candela value needed = Illuminance level desired x distance squared
• CD = E x D2
• E = 150 Foot-candles
• D2 = 7 ft2 = 49 sq. ft.
• CD = 150FC x 49 sq. ft.
• Candela value needed = 7350 Candelas
Luminaire and Lamp Type
• Candela represented in form of a distribution diagram
• Provided by manufacturers
• When sources is not perpendicular (90 degree angle to surface)
• Candela value needed = (Illuminance level desired x distance squared) ÷ cosine of the angle
• CD = (E x D2) ÷ cosine of angle
• E = (CD x cosine of angle) x D2
Point Calculation Example 3
• 10’-0” ceiling
• Accent Fixture
• Above a plate on a table 3; above the finished floor (A.F.F.)
• 30 degree angle for fixture
• 100 foot-candles
• Candela value needed = (Illuminance level desired x distance squared) ÷ cosine of angle
• CD = (E x D2) ÷ cosine of angle
• E = 100 FC (foot-candles)
• D2 = 8.1 feet = 65 sq. ft.
• Cosine of angle = cosine of 30 degrees = 0.87
• CD = (100 FC x 65 sq. ft.) ÷ 0.87
• Candela value needed = 7471 Candelas.