Light Quantity Lighting Metrics Luminous Flux Illuminance

Name: Light Quantity Lighting Metrics Luminous Flux Illuminance
Uploaded: 2017-07-05T06:24:24+00:00
Duration: PTM36S53
Channel: Lindsey Blankenship
Description: Light Quantity Lighting Metrics Luminous Flux Illuminance

Light Quantity Lighting Metrics Luminous Flux Illuminance
Glare vs. Sparkle Lighting Metrics Luminous Flux Illuminance Luminous Intensity Luminance Luminance Exitance

Glare More light is not better.
Uncontrolled bright light in the field of view is glare.

Glare Glare can also be experienced as Veiling Reflection

Glare Knowing the direction of light can reduce the possibility of glare.

Sparkle Sparkle is uncontrolled light that is not visually distracting.

Lighting Metrics

Luminous Flux or how much light does that lamp (light bulb) produce?
watts Notice Lumens 840 Lumens

Luminous Flux Energy In Watts When energy (electricity) flows into a lamp it is converted into light. The total amount of light that flows from the lamp is Luminous Flux. The measure of Luminous Flux is Lumens. Energy Out Lumens (Light)

Luminous Flux or how much light does that lamp (light bulb) produce?
(PHI) = Luminous Flux The measurement of Luminous Flux is Lumens The 60 Watt Soft White Lamp Produces 840 Lumens = 840 Lumens

Luminous Flux If you are looking for the lamp that produces the most amount of light you look for the one with the most lumens. Designers must also be concerned with the energy efficiency of light. A lamp that produces a small amount of light and uses a lot of energy is not efficient. With everything else equal, you want to get the most amount of light for the least energy. Energy=$$

Efficacy = (Lumens) Watts Luminous Flux
By dividing the number of lumens produced by the amount of energy used you can determine the energy efficiency or efficacy of the lamp. (Lumens) Efficacy = Watts What is the Efficacy of the Above Lamp?

Efficacy = = 840 Lumens Watts = 60 840 Lumens 60 Watts Luminous Flux
For every watt of energy used this lamp produces 14 lumens. *Always use nomenclature in all calculations.

Luminous Flux We can use this calculation (efficacy) to compare different types of lamps to compare energy efficiency. The rated lumens of lamps can be found in lamp manufacturer catalogs. Lamp catalogs can be downloaded at: General Electric (general web site Philips (general web site Sylvania (

Luminous Flux Compact Fluorescent Efficacy = Efficacy =
Why Mean Lumens? Some lamps create more light when they are new. The mean number of lumens takes into account the light loss over time. Watts = 14 Lumens = 745 745 Lumens Efficacy = 14 watts Efficacy = 53.2 Lumens/Watts

Luminous Flux HID Metal Halide Efficacy = Efficacy =
Watts = 100 Lumens =6200 6200 Lumens Efficacy = 100 watts Efficacy = 62 Lumens/Watts

Luminous Flux Summary of Efficacy
60 Watt ‘A’ Incandescent = 14 Lumens/Watt 14 Watt Compact Fluorescent = 53.2 Lumens/Watt 100 Watt HID Metal Halide = 62 Lumens/Watt The fluorescent is 3.8 times more energy efficient than the incandescent and the HID lamp is 4.4 time more energy efficient than the incandescent.* *Efficacy is just one of many factors to be taken into account when comparing lamps. CCT, CRI, and the ability to optically control the lamp are other important considerations.

Illuminance How much light do you need to eat pizza, read a newspaper, or prepare food? All these tasks require different amounts of light to complete. You know that you need more light to read a newspaper than to eat pizza. But do you need more or less light to cook a pizza than read a newspaper? These questions are ones which ask how much light falls on a surface. The surface may be a pizza, a newspaper, or the counter in a kitchen. When you want to measure the amount of light needed to complete a task, you will need to understand illuminance.

Illuminance The light that strikes an object is illuminance. In the illustration to the right, the light is striking the light meter. The light meter measures illuminance levels. The units for illuminance are footcandles. (fc). As a designer, you will be designing spaces with different tasks. Each of these tasks will require different illuminance levels.

Illuminance To determine recommended Illuminance levels IES (Illuminating Engineering Society) researches and provides guidelines. You can find more information IES at:

Illuminance The guidelines start with broad categories that range from general lighting through detailed tasks. Lux = Lumens per square meter. Footcandles = Lumens per square foot.

6 - Provide Higher level over food service or selection areas.

Illuminance - IES Recommendations
Eating Pizza = Illuminance Category B ( fc) Reading Newspaper = Illuminance Category D ( fc) Cooking a Pizza = Illuminance Category E ( fc)

E = Illuminance Illuminance
Illuminance can be expressed as the following: E = Illuminance (incident luminous flux*) E = Area (square feet) *Incident luminous flux is the flow of light that strikes a surface.

E = E = = 100 fc Illuminance (Incident luminous flux) = 1500 lumens
If 1500 lumens fall on a desk that is 36” X 60” what is the illuminance level on the desk? (Incident luminous flux) = 1500 lumens Area = 3’ x 5’ = 15 square feet E = Area 1500 Lumens E = = 100 fc 15 square feet

Luminous Intensity Area = 3' * 5' = 15 square feet
Luminous Intensity is the force generating the luminous flux, or the force behind the flowing light. An analogy is water flowing from a hose. The pressure of the water in the hose is similar to luminous intensity. It is important to consider both the direction and force when considering luminous intensity. Area = 3' * 5' = 15 square feet

To represent the intensity and the direction of light we use a candle power distribution curve or intensity distribution diagram. Area = 3' * 5' = 15 square feet The candle power distribution diagram is typically found in light fixture photometric data. The light fixture modifies the direction and intensity of light to aid in the reduction of glare and efficiency.

The candle power distribution diagram illustrates both the intensity and direction of light from a light fixture. The center of the diagram aligns with the center of the light fixture. The solid dark lines indicate the direction and the intensity of the light flowing from the fixture. (Similar to water flowing from a hose.) Light from this fixture flows both up and down. Area = 3' * 5' = 15 square feet

Luminous Intensity UP How many candelas are being emitted from the light fixture at 45 Degrees? 600 Candelas Center of light fixture Candelas Light Direction and Intensity (Thick black line) Direction DOWN

Luminous Intensity Analyze the fixture compared to the direct glare zone. Does the fixture produce light in the undesirable zone? NO The fixture also distributes the light in a wide angle upward which reduces the potential glare or hot spots on the ceiling.

Luminous Intensity What you can understand from candela distribution diagrams. Direction of Light (wide beam, narrow beam, up, down, up and down) Intensity of Light in Candelas* in Any Given Direction (candelas and lumens are interchangeable units) Potential for Glare

Luminous Intensity - Inverse Square Law
We know through experience that as a light source moves further away from a given surface the intensity of light on that surface is reduced. The relationship between light intensity and distance can be described in the inverse square law / point calculation method.

The equation for the inverse square law is as follows: E = Illuminance (fc) I E= I / C = Candelas (cd) D2 D = Distance

What is the Illuminance of a surface that is illuminated with a 800 lumen lamp at a distance of 1’? I I = Candelas = 800 cd E= D2 D = Distance = 1' 800 Candelas E = = 800 footcandles 1'2

What is the Illuminance of a surface that is illuminated with a 800 lumen lamp at a distance of 2'? I I = Candelas = 800 Candelas E= D2 D = Distance = 2' 800 candelas E = = 200 footcandles 2'2

What is the Illuminance of a surface that is illuminated with a 800 lumen lamp at a distance of 4'? I I = Candelas = 800 Candelas E= D2 D = Distance = 4' 800 Candelas E = = 50 footcandles 4'2

When the distance of a light doubles from the surface it is illuminating the amount of light decreases by a factor of 4. 800 footcandles @ 1' 200 footcandles @ 2' 50 footcandles @ 4'

We may need to rearrange the formula to make it practical for interior designers. 8'-6" 5'-0" 1'-6" A task on a desk requires 75 footcandles. You can choose to illuminate the task with a desk lamp (portable fixture), a pendent fixture, and/or a surface mounted fixture. Calculate the amount of lumens required for each lamp based on the placements illustrated above.

8'-6" 5'-0" 1'-6" I E = Illuminance = 75 footcandles E= I = D2 X E D2 D = Distance = 8'-6" I = 8.5'2 X 75footcandles = 5,419 candelas

8'-6" 5'-0" 1'-6" I E = Illuminance = 75 footcandles E= I = D2 X E D2 D = Distance = 5’-0” I = 5’2 X 75footcandles = 1,875 candelas

8'-6" 5'-0" 1'-6" I E = Illuminance = 75 footcandles E= I = D2 X E D2 D = Distance = 1’-6” I = 1.5’2 X 75footcandles = 169 candelas

By using lamp catalogs one can find lamps to match the candelas solved with matching center beam candle power ratings. The Center Beam Candle Power (CBCP) is the approximate amount of candelas at 0 degrees to the light source. (The light shining straight down.) These ratings are given for directional lamps such as PAR, R, and MR16. (Spots and Floods)

Find a lamp near 5,419 CBCP. (Center Beam Candle Power) Find a lamp near 1,875 CBCP. (Center Beam Candle Power)

Find a lamp near 169 Center Beam Candle Power.

To generate 75 footcandles: The ceiling mounted fixture requires 6 times the energy compared to the desk lamp. The pendent fixture requires 2 times the energy compared to the desk lamp. 150 watt Incandescent 45 watt Incandescent 27 watt Incandescent

The inverse square law as stated below only works for a light that is at 90 deg to the surface it is illuminating. 3' I E= D2 D = Distance = 3'-0" I = 500 Candelas 500 Candelas E= 9 sq. ft. E=55.5 Footcandles But what if the light is at an angle to the surface?

3' The amount of light that reaches a surface is reduced when it is at an angel to the plane that it is striking. The amount of reduction is equal to the cosine of the angle. 60 deg 3' I E= cos angle D2 D = Distance = 3'-0" I = 500 Candelas Cos 60 deg = .50 500 Candelas E= .50 9 sq. ft. E=28 Footcandles

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 = 37.5 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

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) ÷ D2

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 = 7’ feet = 49 sq. ft. Cosine of angle = cosine of 30 degrees = 0.87 CD = (100 FC x 49 sq. ft.) ÷ 0.87 Candela value needed = 5633 Candelas.

Photometric Data Photometry is the science of measurement of light.
Photometric data is a set of information related to the amount of light emitted from individual fixtures. Independent labs are used to verify and objectively report photometric data from fixture manufactures

Luminance The luminance is only one of two metrics that can be seen by an observer. Luminance is the intensity of light on the surface on an object emitting light. When a lamp is on and you are looking at the lamp you see luminance. Other examples include neon signs, and soda machines.

Luminance Luminance can provide dramatic visual interest, focus and or direction in a space. But luminance can also be the cause of direct glare in light fixtures. If you can see the lamp in a light fixture that is luminance.

Luminance Luminance can be understood as the amount of candelas per square inch on the surface of the object emitting light. When the object emitting light is viewed at an angle the luminance level is reduced. The factor that the luminance level is reduced is the cosine of the angle. Luminance=250 cd/sq.in. Luminance=250 cd/sq.in. X cos 40 degrees cos 40 deg. = .77 Luminance=250 cd/sq.in. X .77 Luminance=192.5 cd/sq.in. 40 deg.

Luminance Exitance Luminance exitance can also be seen by an observer.
It is the luminance flux that is leaving a surface after it has been reflected from a material. Luminance Exitance can be expressed as: E M = X E M= Luminance Exitance (footcandles) (rho) = Reflectance Value E = Illuminance (footcandles) Luminance Exitance

Luminance Exitance The reflectance value is the percentage of light reflected by a material. (rho) = Reflectance Value E Light colors such as white can reflect upwards of 90% of the light. Dark colors such as black absorb up to 85% of the light. All materials absorb light energy, thus the reflectance value will always be less than (1.0). Think of reflectance values are like taxes they take away, never add. Luminance Exitance (M)

Luminance Exitance Every material has a reflectance value. You can find the reflectance value of paints on the back of the paint chip. Manufactures of materials typically publish the reflectance values in the material specifications. Wall Coverings Ceiling tiles/systems Paints Flooring (carpet and tile) If you can not find a published reflectance value you can use paint chips to match the value. Use the published reflectance value of the matching paint for the unknown reflectance value.

Luminance Exitance If a wall is painted white and 100 footcandles are striking the wall how much light is being reflected by the wall? (rho) = Reflectance Value = .88 (88%) E = Illuminance = 100 fc E M = X E M = .88 X 100 fc = 88 fc (footcandles) What is the luminance exitance of a wall that has a reflectance value of 50% and is receiving 40 foot candles? Luminance Exitance (M)

Luminance Exitance What is the luminance exitance of a wall that has a reflectance value of 50% and is receiving 40 foot candles? (rho) = Reflectance Value = .5 (50%) E = Illuminance = 40 fc E M = X E M = .50 X 40 fc = 20 fc (footcandles) Why is luminance exitance important? Luminance Exitance (M)

Luminance Exitance When light a light fixture is used to illuminate a room some of the light reaches the table directly, and some light reaches the table by reflecting off of the walls. The higher the reflectance value of the surfaces in the room the more light that is reflected onto the table. This increased the energy efficiency of the lighting system. When calculating the number of fixtures required for a room you use the reflectance values of the room in the calculation. (Dark materials in the room more fixtures, light materials in the room less fixtures.)

Luminance Exitance When using a indirect light fixture it is important that you use a ceiling with a high reflectance value. The ceiling in an indirect lighting system is part of the light fixture. The ceiling must reflect most of the light for the lighting system to be efficient.

Luminance Exitance Due to selective absorption, the reflected light will take on the color of the surface of the wall. A red wall will reflect red light onto a white table surface. The table top will most likely show up as pink, a tint of red, because it is mixing with some of the direct light from the light fixture. Not just walls, but any large surfaces in a room, will reflect the color back onto other surfaces in a space. A white ceiling may take on the color of the flooring through reflected light.

Luminance Exitance A high reflectance value is not always desirable. Sometimes it is important to control light by limiting reflection.

Luminance Exitance Low light reflectance on the ceiling (a dark ceiling) creates a more intimate atmosphere.

Luminance Exitance High reflectance values (lighter spaces) tend to visually expand space.

Photometric Data Photometric Data may include the following information: Candle Power Distribution Curve Luminaire Efficiency Coefficient of Utilization Spacing Criterion Physical Dimensions Lamp and Ballast Data Efficacy

Photometric Data Candle Power Distribution Curve
Describes the direction and the intensity of light from the luminaire. Candle power distribution curves can also help determine if the fixture may create problems with direct and reflected glare as well as problems with hot spots.

Photometric Data Candle Power Distribution Curve
‘Batwing’ Distribution (Good for Computers)

Candle Power Distribution Curve ‘Even’ Distribution
Photometric Data Candle Power Distribution Curve ‘Even’ Distribution

Candle Power Distribution Curve Potential Problems:
Photometric Data Candle Power Distribution Curve Potential Problems:

Photometric Data Indirect bat wing patter may reduce hot spots (unacceptable bright areas) on the ceiling. Semi Indirect with a bat wing patter down to reduce potential of reflected glare.

Photometric Data Luminaire Efficiency describes the amount of light that is emitted from the luminaire compared to the amount of light that is generated by the lamps. All fixtures absorb some of the light from the lamps. Comparing luminaire efficiencies between fixtures allow for quick energy efficiency ratings.

Photometric Data Coefficient of Utilization (CU)
Coefficient of Utilization (CU) is the ratio of lumens on the work surface to the lumens emitted by the luminaire. The CU is influenced by the reflectance values of materials, size and shape of the room, and the placement of the luminaire. The CU is used in the lumen calculation method that is used to determine the light levels for ambient lighting systems.

Photometric Data High Coefficient of Utilization (CU) values means more light reached the work surface and is more efficient.

Photometric Data Coefficient of Utilization (CU) Table
pcc = reflectance value of the ceiling. pw = reflectance value of walls Typically the chart assumes a 20% reflectance value for the floor. (This is due to typically dark colors and furnishings.) Room Ratios the larger the number the larger the room.

Photometric Data Coefficient of Utilization (CU) Table
Note that small rooms with light colors have a high CU. Large rooms that are dark have a low CU. The CU represents the percentage of lumens that reach the work surface from the fixture.

Photometric Data Spacing Criteria describes the maximum acceptable distance between fixtures when they are laid out in a room. The number provided by the fixture manufacture is a ratio that is multiplied by the distance between the work plane that is to be illuminated and the bottom of the fixture.

Photometric Data Spacing Criteria
If the distance between the fixture and the work plane is 6’ then the maximum spacing criteria would be 6’X1.2 = 7.2’ parallel to the fixture and 6’X1=6’ 90 degrees to the fixture. (Remember that these are the maximum spacing recommendations.) 7’-2” MAX 6’-0” MAX

Physical Dimensions and Finishes
Photometric Data Physical Dimensions and Finishes

Photometric Data Lamp and Ballast Data

Manufacture Photometric Data
Fluorescent with Wrap Around Prismatic Lens Fluorescent with Prismatic Lens Deep Cell Parabolic Fluorescent Semi Indirect Fluorescent Indirect Fluorescent Compact Fluorescent Down Light Incandescent Down Light MR 16 Down Light HID Down Light

Manufacture Photometric Data
HID Down Light Pendent Fixture Wall Washer Placement Guide Calculation Data

Light Quantity Lighting Metrics Luminous Flux Illuminance

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