when pole spacing is not more than 8 times the mounting height .
OVERHANG Poles are generally installed somewhat off-set from the road edge ( curb ) to provide clearance to the vehicle . Luminaire is mounted on the ranging arm to adjust the distance between it and the curb . Sometimes , projection of the luminaire lies inside the road from the curb , which is known as overhang . �e main purpose of overhang is to provide better uniformity of light across the road .
INCLINATION Inclining or tilting the luminaires up from the horizontal is done to increase light coverage across the road width at a given mounting height . However too much tilting will diffuse the light and reduce its distribution along the longitudinal direction of the road . It is recommended that the angle of tilt , with respect to the normal height of mounting , be limited to an absolute maximum of 10 °, a top limit of 5 ° being preferable . In general the angle varies from 10 ° to 15 °.
UNIFORMITY �e even and uniform distribution of light across the area being illuminated is known as uniformity . It is represented on lighting plans by the symbol UO and is a ratio of the minimum illuminance level to the average illuminance level . A UO value of 0.4 or 40 % is recommended to ensure that lighting installations do not create dark patches next to lighter patches . �e evenness of light distribution is almost always more important than the levels of illumination being achieved by the system .
COLOUR RENDERING Colour rendering indicates the extent to which a light source is capable of making objects appear their true colour . Colour rendering is determined by the spectral power distribution or spectrum of the light source . �e colour rendering ability of lamps is measured on the Colour Rendering Index ( CRI ) or Ra scale . �e scale varies from 0 to 100 , where poor colour rendering lamps have lower values while good colour rendering lamps have high values . One hundred is as good as a black body radiator of the same colour temperature . Conclusion Lamp selection should be made mainly based on efficacy and suitability to each situation . A series parallel resonant mode sine wave inverter is well suited for meeting a compact uorescent lamp ' s complex characteristics . To ensure uniform light output throughout the operating voltage range on input DC battery voltage variation from full charge voltage to lower charge limit voltage , inverter frequency will change automatically by voltage to frequency converter , towards the resonant frequency .
FMDZ | Jan - Feb 2017 | Page39