LIGHTING DESIGN CALCULATION



Lighting design is the part of electrical design process and it is done according to the nature of work place. The Residential Lighting Design is done to meet domestic activities like cooking, reading, cleaning etc. In Offices and Corporates, there should have proper illumination free from glare to facilitate clerical works. In Factory, lighting arrangement should be done to increase productivity and improve quality and in Hospital a good lighting system should be installed, especially in operation theatre. In short, whatever may be the purpose; a good lighting design should meet the following conditions.

•Look good

•Provide the proper amount of light.

•Be built and constructed within budget, code, and other constraints.

•Be environmentally responsible.

•Respond to the Architecture and Interior Design

•Produce good color

•Achieve the desired moods of each space

•Be able to control the lights

According to John E. Reichardt, LC, LEED AP, Project Electrical Designer, Wiley|Wilson, definition of Lighting design is

Lighting design is science and art applied to the built environment for the functional and aesthetic benefit of society; it is the application of objective criteria (science and technology) and subjective criteria (art and inspiration) to every phase of constructing a building or outdoor site to efficiently and properly illuminate constructed spaces for the public good. Lighting design is a specialized multi-faceted discipline woven into the fabric of the construction process. It is a crucial component of the process and is worthy of the rewards commensurate with its demands.”


Design Consideration of a Good Lighting Scheme

While designing good lighting scheme, we have to consider the following criteria

1. Intensity of illumination required.

2. Size of the room.

3. Selection of luminaries

4. Mounting height and space fittings.

1. Intensity of illumination required.

Intensity of illumination required in a place depends on nature of work in that area. It is different in houses, offices, schools, hospitals, shops etc... Required illumination levels are available in building and electrical codes of the respective countries.

2. Size of the room.

The geometric shape of the room is an important factor in lighting design. The lumen output of lamp is not fully utilized in work place. Some part is directed to the ceiling and wall, where part will be reflected and part will be absorbed. This is taken in to factor called Utilization Factor (UF).The utilization factor will depend on the luminaire properties, the reflectance of the room surfaces, the size and shape of room, the height of ceiling, arrangement of fittings etc.

3. Selection of luminaries.

Luminaries are an apparatus which distributes, filters or transforms light given by lamps. The light emitted by the lamp is not completely come out of the luminaries because of its condition of use, there is a factor called Maintenance Factor (MF) which gives an estimate of how lighting conditions will deteriorate through use. Maintenance Factor (MF) depends on dust and dirt inside luminaire surfaces, ageing of light bulbs and cleaning of room surfaces, e.g. ceiling. Without detailed knowledge of a maintenance plan, one sets MF = 0.80


4. Mounting height and spacing of fittings

To achieve uniform lighting requires the spacing between the luminaries should not be longer than 1.5 times the mounting height and the distance of a light source from the wall should be equal to one half the distance between two adjacent light sources.

Calculation of Illumination

There is a formula to estimate the illumination pattern in a room. We will be using the lumen method to get the number of the luminaries needed. This method is used in areas where a uniform light intensity needed and it is used for rectangular room with gridded luminaire pattern.


Number of Luminaires, N = (E x A)÷(OxMFxUF)

Where E is the required illumination (lux)

A is the working area (square meter)

O is the Luminous flux produced per lamp (lumens)

MF is the maintenance factor

UF is the utilization factor


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