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Application Basics

The practical function of lighting is to allow us to see the world around us. Four main factors that affect this ability to see are luminance, time, size and contrast.

Size Effects Visibility

Six Factors of Visibility

  • Luminance
  • Time (speed)
  • Size
  • Contrast
  • Color
  • Age

The amount of light or luminance needed for specific visual activities varies, and depends upon the other factors of contrast, speed, size, color and age. Distance - as it is a function of relative size - should also be considered.

The measurement term luminance can be described as the light emitted or reflected from a source or object in a particular direction. 

Tasks performed quickly, such as scanning the small print of a newspaper, require more light than slower tasks such reading a book to your child. In addition, the text in a children's book is generally larger. 

Contrast affects visibility

High contrast tasks - such as reading dark text on a light background - require less light than lower contrast tasks, such as finding a contact lens on a white carpet.   

Age is also a factor in our ability to see.  Older eyes require more light to see equally as well under a given set of circumstances. For more information about this topic, see the "publications" section of the IES website (RP28 Lighting for Senior Living Environments).  

AboveLighting chandeliers provide soft, ambient distribution while adding interest to the overall décor of a range of applications, from residential to commercial spaces such as hotels and restaurants.

Quantity of Light

Quantity of light is evaluated in terms of illuminance, i.e., the amount of light (lumens) on a work plane or room surface.  It is measured in lux (lumens per square meter) in the metric system or footcandles (lumens per square foot) in the English system.

Footcandles (fc) are used as a relative measurement to explain the recommended light levels for different areas and tasks in the home. 

General Lighting (2 - 10 fc) 

Conversation, relaxation and entertainment areas such as living rooms, dens or other sitting areas require just enough general lighting to sit comfortably and see the lovely person sitting next to you. 

Passageways are also considered "general lighting areas" and require enough lighting to navigate safely from room to room. 

Stairways may require some additional lighting, especially if they are steep and/or narrow. 

Specific Visual Tasks (20-80 fc)

The light level required for specific visual tasks depends upon many factors.  For instance, casual reading may require 40 fc for a middle-aged person with normal vision, but 60 fc or more may be required for an older reader.  More difficult or critical tasks, such as sewing may require 75 fc, especially on dark fabric.

Specific methods for lighting individual visual tasks are presented on a task by task basis in the IES "Lighting Handbook", which is available in the publications section of the website. 

Each task in the Handbook includes a description of the task detail, the task plane, range of recommended illuminance levels, lighting design considerations, and typical equipment locations.

SpotlightQuality of Light

Lighting can be described as being "soft" or "hard".  Diffused light is soft. It minimizes shadows and provides a more relaxing and less visually compelling atmosphere.  When used alone, however, the effect can be lacking in interest, like an outdoor scene on an overcast day. 

The artful use of hard light can provide highlights and shadows that emphasize texture and add beauty to form, as with direct sunlight.  Small unshielded sources such as a bare lamp or a candle flame can add an effect of brilliance or sparkle. 

Creating a Comfortable Atmosphere

Washing the perimeter of a room with light using well-shielded directional luminaires can create the feeling of a bright, open space, and also have the benefit of producing soft, reflected light on faces.

Lighting can create an illusion making a space appear larger or smaller.  Uniform, peripheral lighting enhances this sense of spaciousness. 

Conversely, high levels of focused light can make a space seem smaller and more intimate. Such sources are seldom used for primary illumination.  They are generally decorative and must be supplemented by other illumination. 

With more than one lighting system in a given space, distinct changes in atmosphere and mood can be created.

The Enjoyment of Color

Our eyes permit us to see not only the shapes and surface characteristics of objects but also to perceive color and its relative brightness.  Color contributes greatly to the quality of life - the thrill of a pink sunset or a blue sky.

Lighting professionals use two basic measures to describe and evaluate color: color temperature (chromaticity) and the color rendering index (CRI). 

Color plays an important part in our selection of furnishings, walls, and window treatments in a variety of applications - and since all color comes from light, it is an important part of our lighting decisions as well. 

Enhancing Architectural Features

Light is more than a just a necessary part of the seeing process, it shapes the way we view the world around us and can dramatically increase the enjoyment of your home - not to mention impress the neighbors.

Unique architectural features in your home can be given special attention with light, such as the niche lighting effect seen here.