Light distribution curves, illumination and isolux diagrams

Transcription

1 Light distribution curves, illumination and isolux diagrams β = 5 /7 cd/klm 1 36 cd/klm C 18 - C C 7 - C 9 C C Fig. 1 Fig. 5 Light distribution curves Careful planning work is required to solve lighting tasks. The necessary information about the properties of luminaires is given in light distribution curves, illumination and isolux diagrams. We have explained the knowledge required on this page. specify in what direction and with what intensity a luminaire emits light. The luminous intensity value in candela [cd] for a given luminaire is obtained through the multiplication of the value read off the diagram in cd/klm with the total luminous flux in kilolumen [klm] of the lamps used in the luminaire. Light distribution curves are usually presented in a polar coordinate system (Fig. 1). With floodlights, we specify the light distribution using Cartesian coordinates (Fig. ). In the diagrams, the half beam angles are also shown: continuous line, C 18 - C β = 5 dotted line, C 7 - C 9 β = 7 The luminous intensity values are given on the vertical axis, and the illumination angle on the horizontal axis. In a polar representation, the diagram specifies what sections through the luminaire (C-levels) the curves refer to. 16

2 .6 Information about light and illumination Light distribution curves, illumination and isolux diagrams lx Ē β = 8 /9 cd ,5, m m Fig. 3 Fig. Fig. 5 6 H =, m lx Illumination diagrams for floodlights (Fig. 3) specify the dimensions of the area limited by the two half beam angles (Fig. ) and the average degree of illuminance depending on the distance from this area. Using the parameters floodlights area horizontal axis it is possible to read off: the height (continuous line, C - C 18 β = 8 ) and the width (dotted line, C 7 - C 9 β = 9 ) of the limited area on the vertical axis on the right the average degree of illuminance (parabola) in lx on the vertical axis on the left Example: At a distance of 8 m, the half beam angles of the floodlight limit an area of 3 m in height and 1 m wide. The average degree of illuminance on this area is 1 lx. Uniform illumination can be obtained if the distances between the floodlights correspond to the width of the area limited by the half beam angles. When a façade is illuminated from the ground, only about one third of the specified degree of illuminance can be achieved. Isolux diagrams (Fig. 5) specify the distribution of the illuminance on a visible surface. Points with the same illuminance are connected to each other by means of curves (isolux lines). The luminaire is located vertically above the drawing layer at the mounting height (h) above the coordinate origin. Depending on the luminaire type, the mounting height (h) or the appropriate pole height (H) is specified. The light point interval is approximately twice the distance at which the isolux line which belongs to half of the value of the desired minimum luminance runs. Example: In the isolux diagram shown here, the.5 lx line runs laterally at a distance of 15 m from the coordinate origin. If a path is to be illuminated E min 1 lx then light point spacing of approx. 3 m must be selected. With luminaires with rotationally symmetrical light distribution, the resulting isolux lines are concentric circles. 17

3 In practice Determination of the distance of a floodlight from the illuminated surface on the basis of a light distribution curve lx Ē 1 m m Height Width Half beam angle = /97 8 m 3 m The floodlight with flat beam light distribution has a half beam angle of to 97. The advertising sign / company logo to be illuminated has a height of 3 m (blue line) and a width of 1 m (red line). At a distance of 8 m, the half beam angle corresponds exactly to the dimensions of the advertising sign. The parabola specifies the average degree of illuminance in lux; these values can be read off on the y-axis on the left. The average degree of illuminance of the advertising sign is 1 lx. Changes in the distance of the floodlight influence not only the average degree of illuminance but also the size of the illuminated surface. The following must be noted: the larger the half beam angle, the more stray light is created. The sign will still be well illuminated with a size of x 1 m. 18

4 .6 Information about light and illumination Light distribution curves, illumination and isolux diagrams Determination of the luminaire spacing a for pathway illumination of E min = 1 lx on the basis of the isolux diagram H =,8 m 3 1,5 1 5, lx 3 m m ½ a ½ a a The bollards line the pathway and cast their light asymmetrically onto the ground. For planning purposes, the 1lx line and the.5 lx line are decisive. At 3 m, degrees of illuminance of.5 lx add up to 1 lx on the opposite side of the path. The luminaires should be positioned with a light point spacing of a maximum of 6 m. The specified maximum degree of illuminance can be taken as a planning reference for good uniformity. The average degree of illuminance results from the arithmetic average of all degrees of illuminance on a surface, calculated from the number of measuring points on the x axis and on the y axis. 19

5 In practice Determination of the luminaire spacing a for square illumination with BEGA light building element on the basis of the isolux diagram ,5,8, ,15 lx 1,5 lx m a = 18 m a = 18 m a = 18 m For luminaires with rotationally symmetrical light distribution, the isolux diagram shows one quarter of the total luminous intensity. The average degree of illuminance for a square situation should be 1 lx. About lx is reached directly at the luminaire. In order to obtain an average of 1 lx, the minimum illuminance between two luminaires should be about to 3 lx. In the diagram, the red circles indicate these values. Consequently, luminaire spacing is 18 m

6 .6 Information about light and illumination Light distribution curves, illumination and isolux diagrams Determination of the luminaire spacing a for square illumination with BEGA pole-top luminaires on the basis of the isolux diagram 1 lx H = 5, m a = 3 m 1 5 8,,5 15,5, lx 1 lx m a = m a = m The same principle applies for asymmetrical light distribution. In this case, the position of the luminaires varies. The luminaires are arranged singly along the edge of the square and in double versions on the surface of the square. 131