A lumen is a unit of measurement that is used to express how bright a light source is. An easy way to illustrate this measurement is to imagine a birthday cake with candles. A lamp that puts out one lumen of light is as bright as one birthday candle. A lamp that puts out 100 lumens of light is as bright as 100 candles. Thus the higher the amount of lumens, the brighter the light.
Colour Rendering (CRI)
Colour Rendering Index (CRI) is a way of measuring how vibrant a light source makes colours appear. In other words, it’s a measurement of the light colour quality. The index ranges from 0 to 100. A light’s CRI can only be compared to another light if they have the same colour temperature, which is explained below.
Colour temperature is the colour appearance of the light emitted by a source. The colour temperature of lights can generally be categorised as warm, neutral or sources. Normally, the lower the colour temperature, the warmer the light appears and vice versa. Colour temperature is measured on the Kelvin (K) scale (see diagram).
Design Lifetime is the average life of a lighting product when operated at nominal lamp voltage. A light’s lifespan will depend on its type. Incandescent lightbulbs are very cheap and will last approximately one year. In contrast, LEDs have a high initial cost but will not need to be changed for 30 years.
Luminous efficacy measures how efficient a light source is at converting electricity power to light. It is measured in lumen output per unit power input (watt). Efficacy = lumen / wattage
Incandescents = 12.8 lm/W
Halogens = 14.4 lm/W
Compact Fluorescents = 45 lm/W
Brightgreen LEDs = 68 lm/W
Beam angle refers to a light source’s measure of spread and is measured in degrees. A light’s beam angle is determined when its lux level drops to half of the intensity of the centre beam (see diagram). Beam angles are commonly 15, 30, 45 and 60 degrees.
Lux is a measurement of the light intensity falling on a surface. This measurement determines the brightness of a light in a space and is dictated by Australian standards. Lux meters are available to determine lighting levels and evaluate the energy efficiency of lighting designs.
• One lumen per square meter = One lux
• One lumen per square foot = One footcandle
Daylight harvesting is a technology that senses and recognises light levels as they change throughout the day. A daylight harvesting sensor automatically dims LED lights to maintain an exact light level depending on the amount of light needed in that room at that specific time.
Dimmable lights can be adjusted to the right intensity and deliver different amounts of light for different occasions and times. The range of light levels a bulb can produce will be affected by its dimmability.
A gimballed light allows its direction to be adjusted to a certain degree. Gimbals are useful if you need the light to be projected in a certain direction, such as if light needs to point down a hallway.
A watt is a unit of electrical power. We measure electrical usage in watts and pay for our electricity according to the number of watts we use. Typically, a standard halogen incandescent bulb operates at 50 watts. In contrast, LEDs can be just as bright while using about a quarter of the watts.