HEDI Main catalogue Page 136
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FAQ Frequently asked questions: Luminaires What should I look for when choosing a luminaire? Nowadays, light is a wide-ranging field that is so large that it is easy to lose track of it all. On these pages we would like to explain some terms to help you decide which is the right lighting product for you. / Beam angle When deciding which luminaire is the right one for your application, the area to be illuminated is an important aspect. The beam angle provides information about the angle at which light is emitted forward by a luminaire. The distance of the luminaire to the illuminating object is also a fundamental factor. For uniform illumination of large areas, wide-beam luminaires with a large beam angle should be used. The half-value angle defines the angle at which a spotlight emits at least half of its maximum luminous intensity. Beam angle / Illuminance (lux) Illuminance defines how much light falls on a point of a surface. Since illuminance depends on room characteristics and the effects of other light sources, such as daylight, a decision should rather focus on luminous flux and beam angle. The standard for determining luminous intensity specifies that a luminaire or light source be tested in a completely darkened room in order to measure its values. / Colour temperature (Kelvin) The light colour describes the colour appearance of the light from a light source and is described by the colour temperature in Kelvin (K). It is a decisive criterion for the choice of a luminaire. The Kelvin value of a light source indicates whether it emits a cool or warm light. The lower the Kelvin value, the more the light tends towards "warm white". If the value is higher, the light appears cooler ("cold white"). At workplaces, the most suitable luminaires are those that promote concentration and resemble "daylight white" or "neutral white". HEDI calls this colour temperature of 6,500 Kelvin "Work White". / Luminous efficacy (lm/W) The ratio between lumens (luminous flux) and watts (power consumption) is called luminous efficacy and best describes energy efficiency. The higher the lumen/watt ratio, the better a light source converts the electrical energy introduced into light. / Luminous flux (lm) Luminous flux is measured in lumens (lm) and describes the light output of a light source independent of the beam angle. This allows conclusions to be drawn about the brightness of a luminaire. The higher the lumen value, the more light a luminaire emits (per time unit). At the time of the light bulb and fluorescent lamps, the unit watt was sufficient as a decision criterion to be able to draw a conclusion about the brightness. At the time: The more watts, the brighter the luminaire. That is no longer true these days. / Colour rendering The colour rendering of a light source characterises the colour effect that its light causes on objects. The colour rendering index (Ra or CRI) indicates how naturally colours are reproduced in the light of a light source. This plays an important role in painting activities, for example. A high colour rendering index of at least 80 should be used for this. The scale goes up to 100. Kelvin scale 136 50°
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