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