Getting the lighting right
Ever wondered why your blue socks are so hard to distinguish from the black ones in the morning – even though you installed special spots in the bedroom to illuminate the inside of the wardrobe? It could be that the lamps are not powerful enough – or that they have the wrong colour rendering index. Never heard of that? A brief introduction to lighting quality features will show you what you need to pay attention to in order to get your lighting right.
Light colour describes the colour appearance of a lamp's light. It is based on colour temperature expressed in degrees Kelvin (K): warm white (less than 3,300 K), neutral white (3,300 K to 5,000 K) and daylight white (over 5,000 K). Light colours affect our mood: warm white light is found soothing, cooler colours stimulating.
The colour rendering property of a lamp indicates how natural colours appear under its light. If skin looks colourless, for example, this has nothing to do with the cool light colour of the lamp; it is due to poor colour rendering. Colour rendering index is a measure of lamp quality: Ra = 100 is the best rating. For domestic interiors, at least Ra 80 is required. Halogen lamps achieve Ra 90-100, most energy-saving lamps Ra 80-90.
Luminous efficacy is the measure of a lamp's energy efficiency. It indicates how much luminous flux (= lumen, lm) per watt a lamp generates (= lumen pro Watt, lm/W). Examples: conventional incandescent lamps achieve around 12 lm/W, halogen lamps 20 lm/W, energy-saving lamps 60 lm/W and linear fluorescent lamps around 90 lm/W.
Illuminance considerably affects how swiftly, surely and easily our eyes accomplish a visual task – e.g. reading or working at a computer. It indicates the amount of light falling on a given surface and is measured in lux (lx).
Avoidance of glare
Glare impedes visual performance and, on prolonged exposure, leads to fatigue and loss of concentration. So glare always needs to be avoided. Make sure that lamps do not dazzle and that luminaires are positioned so that their light is neither a source of direct glare nor a cause of reflections on shiny surfaces.
Light and shadow
Uniform brightness makes a room feel uncomfortable. Both light and shadow are needed to give objects shape and depth and to bring the room to life. The ideal solution for the home is a combination of diffuse indirect light (e.g. ceiling floods) and highly focused direct light (e.g. downlights or spots).