FUNDAMENTALS OF LIGHTING

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lighting-fundamentas

Fundamentals of Lighting

The Function of Lighting

We need light to see the world around us. Light is a natural phenomenon vital to our very existence. The advent of a wide range of electric light sources means we are now less dependent upon light from the sun, moon and stars and flames from combustible fuels. The quality, quantity and intensity of light around us greatly affects our visual appreciation of our surroundings. It is important for us to understand the relationship between light, colour, what we see and how we see it. Artificial lighting would not be required if our buildings were not occupied or visited by human beings. The sole purpose of lighting installations is to allow people to adequately perform physical or visual tasks, and the effectiveness of performing these tasks correlates to the quantity and the quality of the lit environment. In the ideal world lighting installations should be designed primarily for the comfort of the occupants within. The task efficiency, energy efficiency and aesthetic value of the lighting installation a secondary consideration. However, the importance of energy efficiency is greatly increased with issues such as climate change and energy pricing, which all impact in our community. The major aim of lighting is to provide the correct lighting solution for the installation to attain the highest quality product, or image, whilst realising the need for energy efficiency. The quality of the lighting system is paramount – the quality of output, morale of the employees and perceived working conditions are all directly related to the lighting system installed.

In this section, we will directly inform you with basics of lighting. The aim of that is to help you to understand where the light and lighting exist and teach you the general principles of Lighting. Both discussing with someone and/or working with a lighting design software,  you need the basics of Fundamentals of Lighting. This post directly created due these needs.

Photometric quantities

Solid Angle

Pyramid or cone which passes luminous flux inside of it is called solid angle. Solid angle’s symbol is “Ω”. Solid angle is directly proportional with the size of the surface (A) and inversely proportional with the length (r).

fundamentals of lighting

If solid angle gets sight of plane, then the value of solid angle defines as streadian (str). For instance assume that , then equation becomes:

streadians in solid angle

Planar angle should be measured as curl in unit circle. On the other hand, planar angle should be measured as surface of sphere in unit sphere.

solid-angle-in-unit-sphere

As shown in the figure above it can be seen solid angle dimensions changes at unit sphere.

solid-angle-in-unit-sphere-2

If we put h value on S equation, equation becomes as:

solid-angle-in-unit-sphere-3

Solid angle sees this surface becomes as:

solid-angle-in-unit-sphere-4

Then, the relation between solid angle and planar angle defines as:

solid-angle-in-unit-sphere-5

Luminous Flux

Tight source is a conversion of energy into a luminous flux. Every light sources work with this principle in daily life. Definitely, none of light sources can convert all of energy into flux. Some of the loss of energy is consumed as heat and some of them absorbed. After loss of energy, rest of energy converted into flux. Although, rest of converted energy into flux, there is also a loss due to radiation of light can be only seen between 380nm and 780nm. Only the product of radiation interval can be seen by eyes which means there is a waste of radiation that does not seen from eyes. The flux that can be seen is called as “Luminous Flux”. Luminous flux symbol is shown as “φ”. The unit of luminous flux is lumen (lm).

 

The Amount of Light

The amount of light should be described as total luminous flux which is created by a source. The amount of light will be shown with “Q” and unit is “lumen-hour (Lmh)”.

luminous-flux

As it could be understood by formulas above, the amount of light is related with luminous flux and the effect of time of this flux produced by a source. If the luminous flux does not change with time this statement takes form as below;

luminous-flux-2

Luminous Intensity

Intensity of a light is measure of luminous flux which is spread in solid angle produced by a light source. The unit of luminous intensity is “candela (cd)”.

luminous-intensity

In case of a lumen luminous flux which spreads 1 steradian solid angle, then luminous intensity takes the form as:

luminous-intensity

Moreover, than the average luminous intensity is:

luminous-intensity-2

Illuminance

Total luminous flux in a specific area is called bright intensity. Device to measure the illuminance is called as “lux-meter”. Unit of illuminance is “lux(lx)”.

illuminance

If the illuminance equals of every point in the area, then equation converts to:

illuminance-2

Here is the table of bright intensity of some of important places given below:

Places

Luminous levels(Lux)

Classes

500

Bedroom

50

Living room

100

Stairs

100

Kitchen

300

Library

500

Laboratory

500

Bath

100

Store

300

Market

750

Waiting room

200

Textile studio

750

Office

500

Luminance

Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square meter (cd/m2 or nit).

luminance

If the value of luminance equals in every point of area, then equation becomes:

luminance-2

Surface Characteristic

Reflection factor

Luminous flux produced by a source from any direction to a surface or an object reflected from a surface is called reflection. Reflection factor is the ratio of coming luminous flux value to reflected luminous flux. After given description about reflection factor, it should be informed that reflection event shows differences due to physical features of surface given below:

  • Specular (direct) reflection
  • Diffuse reflection
  • Mixed reflection

surface-reflectance

As shown in the figure above, there are types of reflections when light faced with different type of surface materials.

Permeability Factor

Permeability factor means the ratio of luminous flux from the source to a diffraction luminous flux from that surface. Furthermore, the factor may vary with the physical feature of that surface. Light may feature of:

surface-reflectance-2

 

Absorbing Factor

The ratio of absorbing luminous flux to incoming luminous flux gives absorbing factor. Absorbing factor is directly related with color of surface.

surface-reflectance-3

 

As a conclusion, if both of three factor combined together we will get figure as:

surface-reflectance-4

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I am electrical engineer, lighting designer, innovator, editor, blogger and an entrepreneur. After, I graduaded from Engineering I started to my career. However, there are plenty of website about lighting and architecture, I was stuck on gathering information about lighting. Due that, I created Lumenhub and combine all datas that I gethered through years. Thx for your interests on my site and please don't forget to be social :) Moreover, If you really liked the works in Lumenhub, please don't forget to donate.

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