Technical parameters of LED luminaires
2019-11-25

Colour of light

Two ratings are used to describe the colour of white light sources:

correlated colour temperature (CCT)
colour rendering index (CRI).

CCT, measured on the Kelvin (K) temperature scale, describes the ‘shade’ of white light emitted.

Common colour temperatures and their typical uses
CCT (K)	Colour designation	Appearance	Typical uses
2,700–3,200	Warm white	Similar to incandescent	Household rooms
4100	Cool white	Neutral light	Offices, garages, workshops
5,500–6,500	Daylight	Cold, harsh, unrelaxed light	Bathrooms, laundries

The material and colour of your furniture can play a role in your decision to use warm or cool lights, since the variation of lighting colour can make room colours appear very vibrant or quite dull.

Correlated colour temperature

Unit: Kelvin

Role: scale to describe how ‘warm’ or ‘cool’ the light source appears

Origin: in theory, as an object (e.g. piece of metal) is heated, it glows, changing colour from a red to orange to yellow to white to bluish-white as the temperature increases.

CCT of typical residential lamps:

Incandescent lamps: operate by heating the filament to 2,700K and by definition, have a colour temperature of 2,700K

Fluorescent, CFL and LED lights: available in a wide range of colour temperatures.

Cool white colour temperature lamps create a feeling of cool, with a colour that is more of a blue tint. Warm white colour temperature lamps create a feeling of warmth, with a colour that is more of a golden tint.

Cool white (left) and warm white (right) colour temperature lamps give rooms a different appearance.

Match the lamp’s colour temperature to the tones of your room. Warm colour temperatures render warm colours like reds, yellows and browns well; cool colour temperatures render cool colours like greys, greens and blues better. In rooms following these general rules, furnishings appear more vibrant. If you have a mix of furnishings, use lamps that produce light in approximately the 3,500K range.

No matter what colour temperature light you choose, if it has a low colour rendering index, nothing will look good under it.

Colour rendering index

Unit: none

Role: scale between 100 and below 0 where 100 represents true natural colour reproduction for that particular colour temperature

Origin: a reference source such as sunlight is defined as having a CRI of 100; incandescent lamps radiate a similar spectrum of light to the sun

CCT of typical residential lamps:

Incandescent lamps: 100 Fluorescent, CFL lamps: 60–95 LED lamps: 80–90

The colour rendering index rates the portrayal of colour.

CRI rates the ability of the light to accurately portray colours of objects in the space being lit.

A CRI of higher than 80 is usually adequate but for specialised tasks where colour is important (food preparation, applying makeup, painting) it is advisable to choose lamps with a CRI above 90.

Lamps of the same colour temperature can vary in their ability to render colours correctly.

Expand your definition of cost

Buyer decisions are often driven by the price tag on an item, without regard for lifetime costs. Lamp technologies differ fundamentally in their lifetime and power consumption, and both have a significant impact on the true cost of providing light over an extended period. For example, at present the initial price of a halogen lamp is significantly lower than the price of an equivalent LED lamp but an LED lasts 5 to 10 times longer and consumes one-fifth the energy. The true dollar cost thus favours LED. The graph analysis for replacement lamp alternatives to a 75W tungsten filament incandescent lamp (no longer available) shows a starting cost of the price of a lamp, each step representing the replacement cost for another lamp, and the rising continuous line indicating the electricity costs of running the lamp.

Graph comparing lamp technology operating/replacement cost.

Note All lamps have equivalent light output. Banned 75W incandenscent for reference only

Operating and replacements costs for lamp technologies, based on lifetime and price of 25,000 hours and $50 for LED, 8,000 hours and $6 for CFL, 2,000 hours and $4 for halogen, and 1,000 hours and $1 for incandescent lamps; and electricity rate of $0.2275/kWh.

The lamp use of 5 hours per day as the basis for the graph is typical for commonly used areas such as kitchens and lounge rooms (based on 2012 Residential Energy Monitoring Program, Lighting data collection and analysis study). In rooms with fewer hours of use, the cost shown on the graph will decrease by the same proportion (e.g. half the hours of use per day: half the cost at each point in time).

This type of analysis can be extended to look at the cost for particular lighting arrangements for each room. The table compares three lighting designs for a 5 x 5m living room with four feature items that could be highlighted, for 5 hours operation a day.

Replacement costs for three lighting designs (does not include cost of fittings)
Design	Ambient lighting	Accent lighting	Total wattage	Initial lamp cost	Annual running cost
A	9 x 50W MR16 halogen	nil	~ 450W	Under $50	~ $200
B	1 x 72W halogen	4 x 20W MR16 halogen	~ 150W	Under $50	~ $70
C	1 x 23W CFL	4 x 6W MR16 LED	~ 50W	$200	~ $25

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Technical parameters of LED luminaires2019-11-25

Colour of light

Correlated colour temperature

Colour rendering index

Expand your definition of cost

Technical parameters of LED luminaires
2019-11-25