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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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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
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 1 solving for illuminance e level
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)
lumen method example 2 solving for lumens or luminaires needed
Lumen Method Example 2Solving for Lumens or Luminaires needed
  • 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
lumen method example 2 solving for lumens or luminaires needed1
Lumen Method Example 2Solving for Lumens or Luminaires needed
  • 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
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
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
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
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
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
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
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.