A good lighting design should: Look good – both people and design space Provide the proper amount of light in every room Be built and constructed within budget, code, and other constraints in mind Be environmentally responsible Respond to the architecture and interior design Produce good color Achieve the desired mood of each space Allow lighting control
Lighting Concepts General Lighting Task Lighting Workplane Distance Footcandle Lumen Candlepower (Candelas) Watts Lamp Data Tables
Lighting Concepts general lighting Every room must have enough illumination to navigate through it. The amount of light will vary depending on the activities performed in the room. General lighting is measured at the workplane level. If there is no workplane like in the livingroom it is calculated at 30 above the floor. General lighting is measured in footcandles
Lighting Concepts general lighting Even light distribution is the key to great general lighting. Fixture placement and spacing must be accurately placed based on the lamps cone of light.
Lighting Concepts task lighting Working at the sink Working at a desk Working at a prep area Reading
Lighting Concepts workplane Workplane – The actual or implied surface on which work happens Distance = Lamp Ht. – workplane height Distance = 96-36 = 60
Lighting Concepts footcandles How do we measure the light on a work surface? Footcandle – a unit of measurement that describes the amount of light on a surface, workplane, art, etc. Lux – The European Footcandle Lux = FC x 10.76 FC = Lux x.0929
Lighting Concepts footcandles Sphere w/ 1 foot radius 1 SF of sphere surface 1 Footcandle is the amount of lighting falling on that surface There are 12.57 of these one radius square curved planes in any sphere. They are known as Steradians
Lighting Concepts lumen Lets talk about another form of measurement in lighting Lumen – a unit of measurement defining the quantity of light a lamp produces. In order to achieve the proper amount of footcandles necessary to illuminate a work surface we must know the strength of the light source. Only then can we determine how many are needed and how far apart they are spaced.
Lighting Concepts candlepower Candlepower – the measurement of a lamps intensity, but only if it is directional
Lighting Concepts beam angle A directional lamp focuses or redirects its light energy into a cone emanating from a lamps lens where it is measured in candlepower. The center of the cone has the most intense light The edges have the least
The beam angle is defined where candlepower drops off to 50% From 50% to 10% is called spill light
Lighting Concepts watts Wattage tells us how much power or energy is burned by a lamp Wattage tells us nothing about the amount of light a lamp can produce A 60 watt PAR38 lamp will have ~ three times the candlepower when compared to a 75 watt R40 lamp.
Color Rendition Index is a scale from 1 to 100 which describes the effectiveness of a light source in reproducing accurately, an objects color. 100 being the best. The sun has a CRI of 100 The best lamps to use are ones with a CRI over 80 Incandescent lamps have a CRI of over 98 Fluorescents are the ones we want to be careful with
Color and Reflectance cri Typical 4 foot fluorescent tube cool white or warm white bulbs have a CRI of around 50 and 60 respectively Color corrected fluorescent lamps are now available in 70 and 80 CRI and those with rare earth phosphorus reach 90
COLOR TEMP. VS CRI Color Temperature describes how the lamp itself appears when illuminated. CRI describes the effectiveness of a light source in reproducing accurately, an objects color.
All together now! Lumens - define the quantity of light Candlepower defines the intensity of light Footcandles defines the amount of light on a surface
All together now! Color temperature describes how the lamp itself appears CRI describes the effectiveness of a light source in reproducing accurately, an objects color.
Reflectance Reflectance – is the amount of light which reflects off an object This quantity of light is measured in Foot-lamberts The amount of light that reflects off of objects in a room adds to the overall illumination So, reflectance must be taken into consideration when determining the Footcandle requirements for a room.
Reflectance Example – 10 x 10 kitchen Ceiling reflectance -The ceiling color is white 80% Wall reflectance Determine the total wall area 10 x 8 = 80 x 4 = 320 SF Divide the room into three predominate materials. 50% is cabinetry (~160 SF) 20% is windows and openings (~64 SF) 30% is wallpaper (~96 SF)
Reflectance Next assign each material a reflectance Natural maple cabinets = 60% Windows & doors = 4 % Dark green wallpaper= 15% Next multiply each reflectance times its percentage of the total square feet.60 x.50 =.30.04 x.20 =.008.15 x.30 =.045 Total =.353 The average wall reflectance is 35%
Reflectance Floor reflectance – 100SF of warm gray slate – use medium gray (25%) Average the totals: Ceiling – 80% Walls - 35% Floor - 25% Average = 47%
Lighting Spacing Principles Calculating Beam Spread Calculate H the distance from luminaire to 6 above work surface With a typical 96 ceiling height and a work surface at 36 the distance would be 54 B = 55° H = 54 2 (tan27.5° * 54) = ~56 = distance between luminaries
Lighting Measurements Inverse Square Law The greater the distance the lamp is from the object or workplane, the more powerful it will need to be The I.S. Law allows you to establish the appropriate lamp candlepower for any distance.
Lighting Measurements Three factors: Candlepower (Cp) Footcandle (Fc) Distance (D) If you know two factors you can calculate the third.
Inverse Square Law Candlepower = Footcandle = Distance =