1. Principles Of Illumination 3u6z4i

PRINCIPLES OF ILLUMINATION

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Illumination -defined as the intensity of light per unit area -simply lighting, that is, man made lighting -Daylight being excellent is not included -Assuming a night time condition Electric Illumination -The production of light by means of electricity and its applications to provide efficient, comfortable and safe vision Lighting Design refers to 2 -The quantity of light -The quality of light

Quantity of Light -Refers to the amount of illumination or luminous flux per unit area -Can be measured and handled because it deals with the number of light fixtures required for a certain area Quality of Light -Refers to the distribution of brightness in the lighting installation -Deals with the essential nature or characteristics of light -Mixture of all the items related to illumination other that quantity of light which 3 includes several elements

1. 2. 3. 4. 5. 6. 7. 8.

Brightness Glare Color Psychological reaction to fixtures Brightness ratio or contrast Diffuseness Aesthetics Economics

color

Four factors that affect illumination 1. brightness 2. Contrast 3. Glare 4. diffuseness

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Brightness -Is the light that seems to radiate from an object being viewed -Brightness or luminance is the luminous flux (light) emitted, transmitted or reflected from a surface Contrast -Difference in brightness or the brightness ratio between an object and its background -The recommended brightness ratio between an object being viewed and its 5 background is normally 3:1

If a print on a white paper can be clearly seen on a light background, it is due to effect called contrast. Likewise, if a light object is placed on dark background, the light object reflects more light and look brighter although both have equal illumination. It is for this reason that office furniture is generally light colored, tan or light green for eye comfort.

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Glare -Is a strong, steady, dazzling light or reflection -Excessive luminance and or excessive luminance ratio in the field of vision There are two types of glare 1. Direct glare – annoying brightness of light in a person’s normal field of vision 2. Indirect or Reflected glare – is much more serious and difficult to control; 7 glossy object

Classification of Lighting System Lighting system is classified into four types, namely: 1. Direct lighting 2. Semi-direct lighting 3. Semi-indirect-lighting 4. Indirect Lighting 8

Direct Lighting - when the light on an illuminated area is focused downward coming directly from the lighting fixtures. - when luminaries direct 90 to 100% of their output downward, they form a direct lighting system. 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

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Semi-Direct Lighting When the predominant light on the illuminated area is fed directly from the lighting units wherein the greater amount of light is obtained from the ceiling through the reflection. The distribution from semidirect units is predominantly downward (60 to 90%) but with a small upward component to illuminate the ceiling and upper walls. The characteristics are essentially the same as for direct lighting except that the upward component will tend to soften shadows and improve room

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Semi-Indirect Lighting Lighting systems that emit 60 to 90% of their output upward are defined as semi-indirect. The characteristics of semi-indirect lighting 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.

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Indirect Lighting. Lighting systems classified as indirect are those which direct 90 to 100% of the light upward to the ceiling and upper sidewalls. In a welldesigned installation the entire ceiling becomes the primary source of illumination, and shadows will be virtually eliminated. Also, since the luminaries direct very little light downward, both direct and reflected glare will be minimized if the installation is well planned. Luminaires whose luminance approximates that of the ceiling

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General Diffuse Lighting. When downward and upward components of light from luminaries are about equal (each 40 to 60% of total luminaire output) the system is classified as general diffuse. Direct-indirect is a special category within this classification for luminaries that emit very little light at angles near the horizontal.

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Since this characteristics results in lower luminances in the direct-glare zone, direct-indirect luminaires are usually more suitable than generaldiffuse luminaries that distribute the light about equally in all directions. General-diffuse units combine the characteristics of direct lighting described and those of indirect lighting described below. 14

Table 7: LIGHT DISTRIBUTION OF VARIOUS TYPES OF LIGHTING SYSTEMS Percent of Distribution Type of Illumination

Upward

Downward

1 – 10

90 – 100

Semi-direct

10 – 40

60 – 90

General diffuse

40 – 60

40 – 60

Semi-indirect

60 – 90

10 - 40

Indirect

90 - 100

1 - 10

Direct

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