Cooper Lighting Design Guide, (accessed July 29, 2009).Ĩ. Gary Gordon, Interior Lighting for Designers, 4th ed. Cooper Lighting Design Guide, (accessed July 29, 2009). The table also indicates the overall efficiency of the luminaire and lamp combination. The zonal lumens summary table in Figure L-LD6 provides a quick overview of lumens in two zones.The spacing criteria indicates luminaire locations for spaces based on uniform illumination requirements. Thus, if the bottom of the Cupola luminaire from the above example is mounted at a height of 8’ above the workplane in an interior space, the recommended spacing is 9.6’ based on the spacing criteria along or parallel to the luminaire being 1.2 and the recommended spacing across or perpendicular to the luminaires is 11.2’ based on a spacing criteria of 1.4. MH (mounting height) refers to the distance between the workplane and the bottom of the luminaire. Distance between luminaires= SC (spacing criteria) x MH (mounting height).The spacing criteria is used to estimate the distance between luminaires in a space as follows: The chart in Figure L-LD6 shows the spacing criteria along (parallel) and across (perpendicular) the length of the luminaire under the photometric data.Photometric cut sheet of a typical direct luminaire by Cupola. Some photometric distribution charts also have the spacing criteria mentioned on the cut sheet see Figure L-LD6 below.įigure L-LD6. Typically, one curve is parallel to the luminaire and another is perpendicular to the luminaire sometime either a third plane at 45° to three planes at 22 ½ ° intervals are added. A luminaire with an asymmetrical distribution, such as a linear fluorescent downlight, requires curves in a number of planes to adequately represent its distribution. Often only one side of the polar graph is shown, since the other side is an identical, mirror image. For luminaires with symmetrical light distributions, a single curve fully describes the luminaire’s distribution.For example, the luminous intensity at 0˚ horizontal angle and 45˚ vertical angle is 832cd. The table next to the polar graph in Figure L-LD5 shows the values of the luminous intensity or candela distribution against the vertical and horizontal angles of the luminaire.Candela distribution of the Quartet luminaire. The lamp is located at the center the lines radiating out from the center depict the angles and the concentric lines depict the decreasing luminous intensity.įigure L-LD5. In the figure below, the curve shown in the polar graph represents the candlepower distribution of the 1T5HO Quartet luminaire which indicates the luminous intensity (cd) in all directions from the center of the lamp. Photometric data cutsheet of a typical direct/ indirect luminaire by Quartet. The voltage, finish and wiring options are included in the “order guide”.įigure L-LD4. The cut sheet below shows the suspended Quartet luminaire with direct/ indirect 2 T5 High Output Fluorescent lamps. įigure L-LD3: Illuminance Cone Diagram ĮXAMPLES OF PHOTOMETRIC DISTRIBUTION IN MANUFACTURER'S LITERATURE: Illuminance Cone Diagram: Usually used for spotlights or lamps with reflectors, the diagram indicates the maximum illuminance at different distances away from the lamp. įigure L-LD2: Cartesian Luminous Intensity Graph This diagram is useful when light intensity changes rapidly within a small angular area. narrow or wide beam etc, in addition to intensity. The curve shown provides a visual guide to the type of distribution expected from the luminaire e.g. It is defined as the illumination of the inside of a sphere of radius 1 foot and a source of 1 CP is fitted at the center of the sphere.Figure L-LD1: Polar Luminous Intensity Graph Ĭartesian Luminous Intensity Graph: The diagram indicates the distribution of luminous intensity, in candelas of the luminaire. Foot Candleįoot candle is also the unit of illumination. The illumination of the inside of a sphere of radius 1 m and a source of 1 candle power is fitted at the center of the sphere is known as lux or meter candle.
Mathematically, illumination is given by the formula, Illumination is denoted by the letter ‘ E’ and is measured in lux or lumen per square meter or meter candela or foot candela. The luminous flux received by the surface per unit area is known as illumination.
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