Close Projection Limit
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The distance (m) from the fixture to a test board (veneered plywood painted black) is measured using 60°C (ambient temperature of 30°C) as the temperature for preventing discolouration and deterioration of fibres and other materials.
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Terms used to describe the properties of light
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Term |
Unit of measurement |
Meaning |
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Luminous flux |
lm (lumens) |
Amount of light emitted from a lamp. |
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Luminous intensity |
cd (candela) |
Strength of light (amount of light emitted in a unit solid angle in a given direction). |
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Illuminance |
lx (lux) |
Brightness of surface being lit. Used as a basic guideline in lighting design. |
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Luminance |
cd/m2 |
Intensity of an object as seen from a given direction. (Where illuminance expresses how much light is reaching a given unit of area, luminance expresses the resulting visible brightness when seen from given direction.) |
Terms used to describe lamps
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Term |
Unit of measurement |
Meaning |
| Rated lamp power | W (watts) | The power consumption of a lamp. Used on labeling and catalogues. |
| Lamp efficiency | lm/W (lumens/Watt) |
Value derived by dividing the lamps total lumious flux by its power consumption (1amp power). This property indicates the luminous flux (measured in lumens) generated by 1 Watt of power. |
| Rated lifetime | h (hours) | Lifetime published in catalogues, derived by average rating the lifetimes of multiple lamps tested under stipulated testing conditions. These stipulated test conditions vary by lamp type and are based on several standards, including the average operating time that elapses until the total luminous flux reaches a stipulated percentage and the operating time that elapses until a stipulated percentage of lamps stop working during a period of continuous operation. |
| Total luminous flux | lm (lumens) | Amount of light discharged by the light source in all directions. Total luminous flux figures given as initial characteristics indicated the luminous flux following 0 hours of operation from standard and halogen bulbs, or following 100 hours of operation for bulb fluorescent lamps, fluorescent lamps, and high-intensity discharge lamps. |
| Colour temperature | K (Kelvin) | Numerical representation of the colour of the light generated by the light source. Colour temperature values decrease as the light becomes redder and increase as the light becomes bluer. Light from different light sources may differ slightly (ie: appear to have a stronger red or blue cast), even if the colour temperatures are the same. |
| Average colour rendering index |
Ra (rendering average) | Numerical representation of the reproductibility (way of seeing) of the colour generated by the light source. This property serves as an indicator of how faithful the colour appears when compared to the reference illuminant (Ra 1000) established by the JIS standard. The Ra unit is not synonymous with a colours desirability; pleasant colours may have low Ra values. 168 INDEX Photometric Data Guide |
Calculating illuminance from product data
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The illuminance of an illuminated surface is inversely proportional to the square of the distance from the light source. Axial luminous intensity (cd) ÷ Square of distance (m) = Illuminance (lx) Illuminance at point A 3.600 ÷ 22 = 900 (lx) Illuminance at point C 3.600 ÷ 32 = 400 (lx) |
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Direct Horizontal Illuminance
| One-half illuminance angle | Top half of the graph | |
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Indicates the spread of light when a light is shone downward onto a horizontal surface, the 1/2 illuminance angle refers to the angle at which illuminance directly under the light is reduced by 1/2. Left side of the graph The graph indicates that for a light source of 2m, illuminance directly under the fixture is about 950lx, with a 1/2 illuminance of 2550 x 2080. |
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Indicates the lamp used for measurements Right side of the graph The graph indicates that for a light source height of 2m, an illuminance of at least 500lx can be obtained in an area with a radius of 1.2m. |
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This graph expresses the relationship between light spread for an upward facing fixture such as an outdoor floodlight and horizontal luminance (lx). (Hotizontal luminance differs from vertical luminance.) |
Light distribution curve
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This graph indicates the light distribution when the spread and strength of the light from the fixture are the same in all cross-sections. The light distribution curve is a graph that expresses strength (luminous intensity) of light from the fixture in all directions. Values read from this graph are for a lamp with a luminous flux of 1,000lm; the actual luminous intensity can be calculated using the following formula:
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| (Luminous intensity) | Indicated luminous intensity X Lamp luminous flux | (cd) |  |
| 1,000 |
Wall luminance distribution (incl. Wall washer models)
This graph indicates illuminance distribution for a fixture installed 0.9m from a wall, as shown in the diagram to the right.
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Utilisation factor
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The utilisation factor table indicates how much of the luminous flux produced by the lamp in the fixture enters the work plane under a variety of conditions. Room index = W x L W : Width (m) |
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The room index obtained from the above formula is used in combination with the reflection rates of the ceiling, walls and floor to obtain the utilisation factor from the utilisation factor table. The following formulas are used to calculate average illuminance and Average illuminance E = F x N x U x M A Required number of lights N = E x A F x U x M E : Average Illuminance (lx) |
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