Indoor Lighting Fixtures Classifications


In the previous topic “Artificial Lighting types and design, I explain the different sources of Artificial lighting and indicate the two forms of it; indoor and outdoor lighting, also I show that the indoor lighting fixtures can be divided to many categories according to the following:

  1. The light function. 
  2. Lamp type. 
  3. Installation method. 
  4. The percentage of light output above and below the horizontal. 
  5. The building type. 

I explained the first factor in the previous Topic and today I will explain the other factors that categorize the light fixtures as follows:

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




2- Classification of Light fixtures according to lamp type:


 

Please review the paragraph “Artificial light sources” in the previous topic “
Artificial Lighting types and design ” for knowing the most common lamp types , of course there are many other types of lamps but we usually didn’t utilize them in design of electrical lighting for construction industry.

Now, we need to know how we can select the proper lamp type for a certain application.

The answer will be as follows:

You should consider several criteria when choosing which light source to use. Note that these characteristics are often a function of the light source itself and the fixture housing it. 

1. Efficacy, Life, Lumen Depreciation
All of these have an effect on life cycle cost. If a lamp's lumen output declines rapidly during its life, the prudent designer initially provides more lumens than is required so that as the lamp declines with age, a sufficient amount of light is still available. In other words, if seven luminaires are required to provide the right amount of light for a space initially, we might put eight luminaires in our design so that the space is over lit at first, but the installation will still provide enough light later on as the lamps provide less than their rated lumen output due to ageing. Comparing the rate of lumen depreciation from one type of lamp to the next thus becomes an important part of the cost analysis. 

2. Amount of Diffusion Desired
It is sometimes desirable to have diffuse light rather than highly directional light since the latter may cause harsh shadows. An area source or a linear source (such as a fluorescent lamp) generates more diffuse light and softer shadows than a point source. 

3. Controllability
Some lamps are more easily dimmed than others. One must consider if simple on/off control is acceptable, if inexpensive dimming is desired, or if it is reasonable to incur the larger expenditures to get higher quality dimming. 

4. Color Rendition
One of the key areas of concern for the architect, interior designer and lighting engineer is the lighted appearance of the space. Most light sources are available in a variety of spectral power distributions, yielding a variety of color-rendering indices (CRI) and color temperatures. The lighting designer must be thoroughly familiar with these concepts in order to properly achieve the desired effect with the chosen lamps. 

5. Distribution Control
Light distribution from a small lamp can be controlled more easily than light emitted from a large lamp. This is simply because it is easier to shape a reflector around a small lamp than a large one. Some lamps are as small as 10 mm in length, and others are as large as 1 m long. The pattern of light from the former can be controlled very precisely whereas the best we can hope to do with the latter is to throw light in one general direction or another. We idealize a small light source with the concept of a "point source." The smaller the light-emitting element of a lamp, the more closely it resembles the ideal of a mathematical point source. 

6. Air Conditioning Load
All artificial lighting adds an additional heat load to a building. Lamps with a higher efficacy will put less heat into a space for a given amount of light output. The most thermally efficient form of lighting is diffuse daylight, followed by direct sunlight, low-pressure then high-pressure gaseous discharge. The worst of all is incandescent lamps. 

7. Consistency and Reliability of Supply Voltage
High-pressure gaseous discharge lamps are more sensitive to voltage variation than low-pressure lamps. If the arc is extinguished due to a dip in voltage, the high-pressure lamp may require up to 15 minutes to return to full light output.

8. Ambient Temperature and Humidity
Some lamps, notably fluorescents, are very sensitive to temperature and humidity. These lamps are difficult to start when the ambient temperature is low, and once started may not produce full light output. 

9. Cost
Some lamps are quite cheap to purchase, initially. However, these tend to have low efficacy and relatively short lives. One must consider not only the initial cost, but the cost to operate the system over its entire life, including energy costs and the requirement to pay a worker to change the burned-out lamps frequently. Fluorescent lights and LEDs are often a cost improvement on incandescents for this reason alone, even without energy savings.

the following table will compare between the characteristics of different lamps as follows:



3- 
Classification of Light fixtures according to installation method

the light fixtures can be classified according to installation method to the following types as follows:


fig (1): Classification of Light fixtures according to installation method 


A- Free-standing or portable (see fig.1)

such as Table lamp fixtures, standard lamp fixtures, and office task light luminaires. 


B- Fixed 
(see fig.1) 

1- Recessed light : the protective housing is concealed behind a ceiling or wall, leaving only the fixture itself exposed. The ceiling-mounted version is often called a downlight.

Cans, downlighting , uplights placed on the floor, Troffer light (recessed fluorescent lights ), Cove light ( recessed into the ceiling in a long box against a wall), Torch lamp (floor lamp).

2- Surface-mounted light : the finished housing is exposed, not flush with surface.

3- Pendant light : suspended from the ceiling with a chain or pipe.

4- Sconce : provide up or down lights; can be used to illuminate artwork, architectural details; commonly used in hallways or as an alternative to overhead lighting.

5- Track lighting fixture: individual fixtures can be positioned anywhere along the track, which provides electric power.

6- Under-cabinet light : mounted below kitchen wall cabinets.

7- Emergency lighting or exit light : connected to a battery backup or to an electric circuit that has emergency power if the mains power fails.

8- High- and low-bay lighting : typically used for general lighting for industrial buildings and often big-box stores.

9- Strip lights or industrial lighting : often long lines of fluorescent lamps used in a warehouse or factory.

10- Soffit : can be general or a decorative wall-wash, sometimes used to bring out texture on a wall, though this may also show its defects as well. The effect depends heavily on the exact type of lighting source used.



4- Types of Light fixtures according to the percentage of light output above and below the horizontal:


the light fixtures can be classified according to the percentage of light output above and below the horizontal  to the following types as follows: 

A- Direct Lighting:

 
  • When luminaires direct 90 to 100% of their output downward. 
  • The distribution may vary from widespread to highly concentrated, depending on the reflector material, finish and contour, and on the shielding or control media employed. 
  • Troffers and downlights are two forms of direct luminaires. 
  • Can have the highest utilization of all types, but this utilization may be reduced in varying degrees by brightness-control media required to minimize direct glare. 
  • Reflected glare and shadows may be a problem with direct lighting unless close spacings are employed. 


B- Semi-direct Lighting:

  • The distribution is predominantly downward (60 to 90%) but with a small upward component to illuminate the ceiling and upper walls. 
  • The same as for direct lighting except that the upward component will tend to soften shadows and improve room brightness relationships. 
  • Care should be exercised with close-to-ceiling mounting of some types to prevent overly bright ceilings directly above the luminaire. 



C- General Diffuse Lighting:



  • When downward and upward components of light from luminaires are about equal (each 40 to 60% of total luminaire output).
  • Direct-indirect is a special (non-CIE) category within this classification for luminaires that emit very little light at angles near the horizontal. Since this characteristic result in lower luminances in the directglaze zone, direct-indirect luminaires are usually more suitable than general-diffuse luminaires that distribute the light about equally in all directions. 
  • General-diffuse units combine the characteristics of direct lighting and those of indirect lighting. 
  • Brightness relationships throughout the room are generally good and the upward light reflected from the ceiling softens shadows from the direct component. 
  • Pendant-mounted luminaires designed to provide a general-diffuse or direct-indirect distribution are frequently installed on or very close to the ceiling. 
  • Such mountings change the distribution to direct or semidirect since the ceiling acts as a top reflector redirecting the upward light back through the luminaire. 


D- Semi- Indirect Lighting:

  • Lighting systems that emit 60 to 90% of their output upward. 
  • The characteristics are similar to those of indirect systems except that the downward component usually produces a luminaire luminance that closely matches that of the ceiling. 
  • However, if the downward component becomes too great and is not properly controlled, direct or reflected glare may result. 



E- Indirect Lighting:



  • Lighting systems which direct 90 to 100% of the light upward to the ceiling and upper sidewalls. 
  • In a well-designed installation, the entire ceiling becomes the primary source of illumination, and shadows will be virtually eliminated. 
  • Also, since the luminaires direct very little light downward, both direct and reflected glare will be minimized if the installation is well planned. 
  • It is also important to suspend the luminaires a sufficient distance below the ceiling to obtain reasonable uniformity of ceiling luminance 
  • Since the indirect lighting the ceiling and upper walls must reflect light to the work plane, it is essential that these surfaces have high reflectances. Care is needed to prevent overall ceiling luminance from becoming too high and thus glaring. 


In the next topic, I will explain the Classification of Light Fixtures according to Building Type and the factors that can be controlled in the lighting design. so, please keep following.


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