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 1 Solving 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 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 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 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.