Light Output Ratio – the percentage of light emitted from the light source that makes it out of the luminaire. An LOR of 70 means 30 per cent of the light from lamp is lost inside the reflector and light fitting.
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.