LIGHTING DESIGN
STANDARDS
the purpose of electric lighting “Illumination ” is good lighting when it
• To extend the useful hours in the day provides adequate illuminance to enable
• To assist the performance of a visual task the task to be performed efficiently,
• To display or reveal something Good lighting design is not simply about
• To control how something appears achieving a required illuminance on the
• To attract attention working plane, it is about creating and
controlling the lit environment.
Standards often specify lighting in terms of the illumination on the horizontal
plane, which is the amount of light falling onto a horizontal surface. This is because
it is easy to measure and easy to calculate. It is not a good indicator of the visual
environment however, as people generally judge the adequacy of the lighting by
the luminance or relative brightness of the vertical surfaces.
•Ballast: A device that regulates the flow of electricity to start and operate
fluorescent and other discharge type lamps.
•Beam angle: The angle of the central cone of light (the beam spread) cast by a
reflector-type lamp, beyond which the beam intensity is less than 50% of the
maximum. Generally, a lamp with a beam angle of less than 25 degrees is considered
a spot; with an angle greater than 25 degrees, a flood.
•Diffused light: Light that is dispersed in a wide pattern with no directional quality,
similar to outside conditions on an overcast day. Glare is reduced, but such light may
tend to wash out and flatten objects.
•Diffuser: A glass or plastic lens over a lamp that scatters light in all directions. In
fluorescent downlights, a plastic or metal grid is often used to block glare and direct
the light downward. Deep-cell parabolic louvers are the most efficient grid
configuration.
•Efficacy: The light output of a lamp per electricity consumed, expressed as lumens
per watt. Fluorescent's are three to five times more efficient than standard “A” lamp
incandescent's.
•Lumens: A measure of the light output of a lamp (light bulb) or other light
source. A candle provides about 12 lumens, a 60-watt soft light bulb about
850 lumens. Details are at Lumens, Definition, comparisons.
•Footcandles: A measure of the total light falling on a surface. One foot
candle (fc) is equal to one lumen per square foot, originally based on the
illumination of one candle held one foot from a surface.
•Luminaire: Any lighting fixture or built-in lighting system, such as a cove or
valence.
•Wattage: A measure of the energy consumption of a lamp or other electrical
device. More efficient lamps produce more lumens for the same wattage
consumed.
Light Level or Illuminance, is the total luminous flux incident on a surface, per
unit area. The work plane is where the most important tasks in the room or
space are performed.
Illumenance is measured in foot candles (ftcd, fc, fcd) (or lux in the metric SI
system). A foot candle is actually one lumen of light density per square
foot, one lux is one lumen per square meter.
1 lux = 1 lumen / sq meter = 0.0001 phot = 0.0929 foot candle (ftcd, fcd)
1 phot = 1 lumen / sq centimeter = 10000 lumens / sq meter = 10000 lux
1 foot candle (ftcd, fcd) = 1 lumen / sq ft = 10.752 lux
The lumen is the unit of visible light. To be rated as high efficacy, a lamp must
produce a certain number of lumens for each watt of electrical power it
consumes. Efficacy is therefore measured in lumens per watt.
LUMINOUS FLUX (Φ)
• The luminous flux describes the quantity of light emitted by a light
source
• The SI unit of luminous flux is lumen (lm)
• One lumen is defined as the luminous flux of light produced by a light
source that emits one candela of luminous intensity over a solid angle
of one steradian
• LUX vs. LUMEN
• lux takes into account the area over which the luminous flux is spread
LUMINOUS FLUX ROOM AREA ILLUMINANCE
1000 lumens 1 SQ. Mt 1000 Lux
1000 lumens 10 SQ. Mt 100 Lux
Common and Recommended Light Levels indoors
Illumination
Activity
(lux, lumen/m2)
Public areas with dark surroundings 20 - 50
Simple orientation for short visits 50 - 100
Working areas where visual tasks are only occasionally performed 100 - 150
Warehouses, Homes, Theaters, Archives 150
Easy Office Work, Classes 250
Normal Office Work, PC Work, Study Library, Groceries, Show Rooms,
500
Laboratories
Supermarkets, Mechanical Workshops, Office Landscapes 750
Normal Drawing Work, Detailed Mechanical Workshops, Operation
1,000
Theatres
Detailed Drawing Work, Very Detailed Mechanical Works 1500 - 2000
Performance of visual tasks of low contrast and very small size for
2000 - 5000
prolonged periods of time
Performance of very prolonged and exacting visual tasks 5000 - 10000
Performance of very special visual tasks of extremely low contrast and
10000 - 20000
small size
Illumination can be calculated as
I = Ll Cu LLF / Al (1)
Example
where 10 incandencent lamps of 500 W (10600
I = illumination (lux, lumen/m2) lumens per lamp) are used in an area
of 50 m2. With Cu = 0.6 and LLF =
Ll = lumens per lamp (lumen) 0.8 illumination can be calculated as
I = 10 (10600 lumens) (0.6) (0.8) / (50 m2)
= 1018 lux
Cu = coefficient of utilization
LLF = light loss factor
Al = area per lamp (m2)
Color Rendering Index
(CRI)
A relative scale indicating how perceived colors illuminated by the light source match actual colors. The higher the
number the less color distortion from the reference source.
85 -100 CRI = Excellent color rendition
75 - 85 CRI = Very Good color rendition
65 - 75 CRI = Good color rendition
55 - 65 CRI = Fair color rendition
0 – 55 CRI = Poor color rendition
Color Rendition
warm light source is used, neutral light source is used cool source is used enhancing
enhancing reds and oranges blues and greens
Color rendering, expressed as a rating on the Color Rendering Index (CRI), from 0-100, describes how a light
source makes the color of an object appear to human eyes and how well subtle variations in color shades are
revealed. The higher the CRI rating, the better its color rendering ability.
Color Temperature (K˚)
A measure of the “warmth” or “coolness” of a light source.
≤ 3200K = “warm” or red side of spectrum
≥ 4000K = “cool” or blue side of spectrum
3500K = “neutral”
5000K = “Daylight”
Color Temperature Scale
13
Lumens-Per-Watt Comparison
Just as an automobile's fuel efficiency is measured in miles per gallon, lightbulb efficiency is
measured in terms of lumens per watt—the amount of light produced for each watt of electricity
consumed. More lumens per watt means more light for your money.
Thank you!!!
