Electrical Load Classification and Types – Part Four

In the previous topic, Electrical Load Classification and Types – Part Three , I indicated the differences between Linear and Non-Linear electrical Loads and explain the effects of using Non-Linear loads in electrical design.

And today, I will explain the electrical loads calcification and types according to the load function.

You can review the following previous topics for more information and good following.

Third Classification of Electrical Loads: According To Load Function

The electrical loads will be classified according To Load Function as follows:

  1. Lighting Electrical Load.
  2. Receptacles / General / Small Appliances Electrical Load.
  3. Power Electrical Loads.

1- Lighting electrical loads

a- What is light?
Visible light is electromagnetic radiation with a wavelength that is visible to the eye

b- What are the main sources of light?
there are two main sources of light which are as follows:

1- Natural light (day light or sun light) source

Sunlight is electromagnetic radiation by sun and which includes the full spectrum of visible light (as well as frequencies beyond the sensitivity of the eye, known as ultra violet and infrared)

2- Artificial light sources

Artificial light sources are other sources of light which developed to compensate for /assist the natural light. It will have different frequencies and wavelengths that determine the light color.

Effects of Using Day Lighting Source in Electrical Design 

1- What is Importance of day lighting in electrical lighting design?

A Particular attention must be given to day lighting while designing a building lighting system due to the following:

  • Day lighting is used to maximize visual comfort inside the buildings. 
  • Day lighting is used to reduce energy use by the following methods: 
  1. Reducing the use of artificial (electric) lighting by simply installing fewer electric lights because daylight is present, or by dimming/switching electric lights automatically in response to the presence of daylight.
  2. Using passive solar technology for heating or cooling different spaces inside the building. 

2- What are the main characteristics of day lighting source?

  • The daylight entering a building may include direct sunlight when the window has a view of the sun, as well as diffuse sunlight that has been refracted by clouds, and reflected from various surfaces such as clouds, ground or other buildings.
  • Daylight can therefore vary greatly with weather conditions, ranging from total cloud cover to clear sky with direct sunlight.
  • The effectiveness of daylight as a light source is measured as the “Daylight Factor”

Daylight Factor

It is the ratio of internal light level to external light level and is defined as follows:

DF = (Ei / Eo) x 100%


Ei = illumiance due to daylight at a point on the indoors working plane,

Eo = simultaneous outdoor illuminance on a horizontal plane from an unobstructed hemisphere of overcast sky.

  • Daylight factors are used to determine if the natural lighting levels in a space will be sufficient for the occupants of the space to carry out their normal duties. 
  • Calculating daylight factors requires complex repetition of calculations and thus is general undertaken by a proprietary computer software product such as Radiance. 
  • CIBSE Lighting Guide 10 (LG10-1999) which broadly bands average daylight factors into the following categories: 
  1. DF Under 2 – Not adequately lit – artificial lighting will be required. 
  2. DF Between 2 and 5 – Adequately lit but artificial lighting may be in use for part of the time. 
  3. DF Over 5 – Well lit – artificial lighting generally not required except at dawn and dusk – but glare and solar gain may cause problems. 

3- What are the types of day lighting technologies?

there are two types of technology that are used for utilizing the day lighting source as follows:

1- Active day lighting

It is a system of collecting sunlight using a mechanical device to increase the efficiency of light collection for a given lighting purpose. Active day lighting systems are different from passive day lighting systems in that passive systems are stationary and do not actively follow or track the sun

2- Passive day lighting

It is a system of both: collecting sunlight using static, non-moving, and non-tracking systems such as Windows, Sliding glass doors, most skylights, light tubes, and reflecting the collected daylight deeper inside with elements such as light shelves. Passive day lighting systems are different from active day lighting systems in that active systems track and/or follow the sun, and rely on mechanical mechanisms to do so.

4- What are the Common Methods for using Passive day lighting technology in a building?

there are many methods for using 
Passive day lighting technology in a building but the common ones will be as follows:

1- Windows
Windows are the most common way to admit daylight into a space. Their vertical orientation means that they selectively admit sunlight and diffuse daylight at different times of the day and year.

2- Skylight  (see fig.1)

fig (1): Skylight Lighting

It is any horizontal window, roof lantern placed at the roof of the building, often used for day lighting. Generally it is made from White translucent acrylic which makes the transmitted light to be perfectly diffused and distributed evenly over affected areas and reduces the transmitted heat inside the building. Skylights admit more light per unit area than windows, and distribute it more evenly over a space.

The optimal area of skylights varies according to climate, latitude, and the characteristics of the skylight, but is usually 4-8% of floor area.

With proper skylight design, there can be significant energy savings in commercial and industrial applications up to 80 percent according to the US Department of Energy's Federal Energy Management Program. In terms of cost savings, the DOE reported that many commercial buildings can reduce total energy costs by up to one-third through the optimal use of day lighting.

3- Light shelves 
 (see fig.2) 

fig (2): Light Shelves 

Light shelves are an effective way to enhance the lighting from windows on the equator-facing side of a structure, this effect being obtained by placing a white or reflective metal light shelf outside the window.

Usually the window will be protected from direct summer season sun by a projecting eave. The light shelf projects beyond the shadow created by the eave and reflect sunlight upward to illuminate the ceiling. This reflected light can contain little heat content and the reflective illumination from the ceiling will typically reduce deep shadows, reducing the need for general illumination.

4- Tubular Day lighting Devices (TDDs)   (see fig.3) 

fig (3): Tubular Day lighting Devices

It uses modern technology to transmit visible light through opaque walls and roofs. The tube itself is a passive component consisting of either a simple reflective interior coating or a light conducting fiber optic bundle. It is frequently capped with a transparent, roof-mounted dome 'light collector' and terminated with a diffuser assembly that admits the daylight into interior spaces and distributes the available light energy evenly.

5- Smart glass   (see fig.4) 

fig (4): Smart glass Lighting Technology

It is the name given to a class of materials and devices that can be switched between a transparent state and a state which is opaque, translucent, reflective, or retro-reflective. The switching is done by applying an electric voltage to the material, or by performing some simple mechanical operation. Windows, skylights, etc., that are made of smart glass can be used to adjust indoor lighting, compensating for changes of the brightness of the light outdoors and of the required brightness indoors.

5- Problems generated from using day lighting source

Two potential problems associated with the use of day lighting buildings are as follows:

1- Glare
Glare occurs when a bright light source such as the sun is in the field of view of users. It can also occur when reflections of the sun are in the field of view.

2- Heat
Daylight is always associated with heat, and the challenge is to maximize the benefit from daylight with minimum heat gain.

all the above information will guide the electrical designer for utilizing the Daylight Source (in cooperation with the architecture engineer) to have  the best lighting design which meet the user requirements and in same time increase energy savings in the buildings.

In the next topic, I will explain the artificial lighting sources and loads. So, please keep following.


  1. Magnificent piece of information. These are not for students but also for professionals. Great job Mr. Ali, all these are free of cost which is really priceless.