Lighting In Interior Design

Good lighting design involves providing both the proper quantity and quality of light to perform a task. Different visual tasks under different conditions require varying levels of illumination. The variables involved in lighting for task performance include the nature of the task itself.

 The age of the person performing the task, the reflectances of the room and the demand for spend and accuracy in performing the task. Apart from task performance, lighting design also addresses.

• The enhancement of a particular space or structure in order to reveal spatial volume, planes, ornament and colour.

• The perception of any given space by visitors, by drawing attention to points of interest.

• The provision of safety and security by increasing visibility and engendering a sense of security, many times against hazards such as a changing floor plane or moving objects.

Light Sources.

In addition to daylight, there are three types of light sources: incandescent, fluorescent and high intensity discharge. When selecting a light source, the designer should consider several important issues, including colour, size, efficiency, life and maintenance.

COLOUR.

Each lamp family has its own inherent colour characteristics. The different light sources render colour qualities differently and create varying perceived colour effects. A color rendering index (CRI) is a quantitative measure of the ability of a light source to reveal the colours of various objects faithfully in comparison with an ideal or natural light source. CRI values depend on the design project at hand as follows:

• a CRI of 50-70 is applicable to industrial and general illumination when colour is of minor importance
• a CRI of 70-79 is applicable to most office, retail, school, medical and other work and recreational places
• a CRI of 80-89 is applicable to retail, work and residential spaces when colour quality is important
• a CRI of 90-100 is applicable to retail and work spaces when colour rendering is critical.

Another way of specifying lighting colour is based on colour temperature, measured in degrees Kelvin. For most interior applications, colour temperatures range from about 2700K to 5000K. The lower the colour temperature is, the “warmer” the light will be. As the temperature increases, the light becomes more blue and white.

Colour temperature should be based on the overall appearance desired and the colours of the finishes and furniture. For most office applications, lamps operating at about 3500K are often specified. In most cases, the designer should specify that all lamps in a space should have about the same colour temperature.

Office Concept by Vetrov Pavel.

Fifty Three Office by Ferian Sonny.

It is also very important to take into consideration the spectral energy distribution curve for each light source when specifying lighting colour for a space, as it directly affects the colour of finishes, furniture and other objects in the space. For example, using a lamp with a high complement of blue and violet will make finishes and furniture with the warmer colours of red appear dull, grey and washed out.

Office design by Gongalov Dimitar.

SIZE.

It is useful to think of light sources classified into point, line or area sources. 

• Point sources, for example bare incandescent lamps, recessed incandescent or high-intensity discharge fixtures with small apertures and specular reflectors, can be precisely controlled in terms of where light is desired to be or not and can provide sparkle in a space by means of reflection off polished surfaces.

Writer by Fernandes Angelo.

• Line sources, such as bare fluorescent tubes and linear fluorescent fixtures, are useful for lighting large open areas where repetitive rows of fixtures are suitable.

Autumn morning by Samun Maksym.

• Area sources, such as a window, are concentrations of light sources covered by a diffusing element. These sources usually provide medium to high level of light with little directional control.

Various images by Sagnotti Emiliano.

Quantity of Illumination.

The most accurate method of determining illumination performance is by computer, with an extensive range of software available on the market. However there is a method, called the lumen method or zonal cavity system which can be used to determine the horizontal illuminance that will result from a proposed lighting fixture selection and layout, as well as the number of fixtures required for a space and its horizontal illuminance value. The three formulas for average lighting calculations are as follows:

• Number of Fixtures: foot candles desired x room area(feet)

CUxLLFx lamps/luminairexlumens/lamp
CU=Coefficient of utilization (percentage of light that actually reaches the task)
LLF= Light Loss Factor

e.g. Number of Fixtures=50x25x40 = 9.35 Fixtures (use 9 or 10)
0.67x0.7x4x2,850

• Power Density:(W/sqft)= number of fixtures x design watts (including ballast)

area of the room
e.g.Power Density:(W/sqft) 9x111or 10x 111 =
25x40 25 x 40

0.999 W/sqft (9 Luminaires) or 1.111 W/sqft (10 Luminaires)

Design Process.

Although there is no one process for designing a lighting installation, there are several important considerations and a series of steps recommended for completing a lighting design.

The first step is to determine the function of the space and the visual tasks to be performed in it. This includes determining the light levels needed (footcandle level), whether the space will be single or multiple use and any special conditions that might dictate a particular kind of a lighting solution. For example, a room with computer terminals will require particular care to avoid glare on the screens. An indirect lighting system with local, adjustable task lighting might be appropriate. Existing conditions that might affect the design should also be studied, such as daylighting contribution, ceiling height, ceiling construction, the size of the room and other physical limitations.

Lighting should enhance the character and function of the space. A lighting design for a library reading room will be quite different from a design for a nightclub lounge. The character of a space includes not only the lighting level, but also the types and styles of luminaires selected. Additional considerations include the degree of uniformity of lighting, lighting control, fixed lighting versus portable lamps and the visibility of the light sources.

Next, lamp types are selected mainly based on the color rendition required, overall economy and type of control required. Luminaire selection then follows, with pieces which complement the design of the space and also address glare control, cost effectiveness and adjustability. Finally, the number and location of luminaires are determined, based on either the formulas provided earlier on in this article or experience and practical considerations.

Bibliography.

• Interior Design Reference Manual, Fourth Edition by David Kent Ballast, AIA
• Interior Graphic Standards, Student Edition, by Maryrose Mc Gowan& Kelsey Kruse
• Wikipedia.