The UGR method (Unified Glare Rating) is an international index presented by CIE, the international lighting research body, in its publication 117 and is used to evaluate and limit the psychological direct glare from luminaires. Contrary to previous methods where the glare was rated using the luminance values of a single luminaire, this method calculates the glare of the entire lighting installation at a defined observer position.
Colour rendering is also important. This is the ability of a light source to show surface colours as they should be, usually in comparison to a tungsten or daylight source. Lamps with poor colour rendering will distort some colours.
Light emitting diode lamps are flavour of the month, and deliver big energy savings, good colour rendering, dimmability and a long life. The best ones are difficult to distinguish from incandescent lamps. But they come with a hefty price tag – of up to £30 a lamp. And many Chinese versions are, well, rubbish.