System efficiency of luminaire

This factor depends on the light output ratio (LOR). This is calculated as luminous flux of the luminaire to the sum of luminous flux of all its light sources. For standardization purposes the reference measurements are made in lab conditions, the most important one being a constant temperature of 25 degrees Celsius.

The ratio can show how well the luminaire is designed and how much light is lost in its optical systems. The more efficient materials are used the higher the ratio. The shape itself is also very important: correctly designed luminaire reflects most of the lamp's luminous flux into the environment. This is the very core of the luminaire's system efficiency.

 

This factor depends on the light output ratio (LOR). This is calculated as luminous flux of the luminaire to the sum of luminous flux of all its light sources. For standardization purposes the reference measurements are made in lab conditions, the most important one being a constant temperature of 25 degrees Celsius. The designing of a lighting installation should take this factor into account; otherwise its calculated illuminance values may be incorrect.

The ratio can show how well the luminaire is designed and how much light is lost in its optical systems. The more efficient materials are used the higher the ratio. The shape itself is also very important: correctly designed luminaire reflects most of the lamp's luminous flux into the environment. This is the very core of the luminaire's system efficiency.

The LOR can be further subdivided into upward and downward ratio, each of them specifying intensity distribution of a luminaire in the upper and lower parts of the room. This is important in cases where good ceiling illumination is required. Light output ratio with LEDs is also influenced by heating of the LED elements – a good management of heat in the luminaire is therefore very important.

Light output ratio of luminaire (LOR) takes into account for the loss of light energy both inside and by transmission through light fittings. It is given by the following expression.

LOR

 

The simple fact that a luminaire is efficient does not automatically mean it is ergonomic as well. Luminaires with high light output ratio can produce glare, which is a drawback when illuminating workplace for example. Typical luminaires with high light output ratio are spotlights and downlights. On the other hand, the luminaires which use specular louvers to prevent glare can provide higher illuminance on the working plane despite lower LOR.

The materials used for luminaire construction are really at the heart of the final light output ratio. Glass, plastics, aluminium and steel all have different light absorbing and reflecting properties. With their proper use as much light as possible can be reflected outside the luminaire and into the environment, providing high light output ratio.

The quality of illumination further depends on how the materials are used. For soft, diffuse lighting the luminaire has to provide material that deflects the light uniformly into all directions, such as matt louvers. The other possibility is to employ a glass or plastic translucent cover with the surface finish that diffuses the light uniformly into the area. If the desired illumination should be concentrated such as in accent lights, the inner surface has to be designed to reflect the lamp light in a single direction. Modern computer programs can help with designing reflectors for luminaires which provide a desired reflection with little loss to light output ratio.

For the purposes of LQS, the luminous efficacy of a luminaire is used, with the highest marks awarded to those providing over 80 lumens per watt. The number for a luminaire is a product of light output of a luminaire and installed power of luminaire. The higher the efficacy of the source and the light output ratio of the luminaire, the better marks can be scored. This means that along quality luminaire design a correct lamp has to be chosen as well. Judged by their efficacy, the best marks can be achieved by those that emit little radiant heat. The production of heat basically means that energy is not being all converted to light, a sign of inefficacious light source.



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