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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

A photo of a face under three different colour rendering areas. A colour rendering index of 50 to 70 is a fair representation of actual colour, the colours appearing a little dull and greyish. A colour rendering index of 70 to 80 is a good representation of actual colour, the colours appearing quite orange. A colour rendering index of 80 to 90 looks like the normal hues of flesh and hair and is classed as excellent.At a colour rendering index of 90, the full spectrum of colour, tones and shades can be seen; tomatoes, capsicums and applies look red; carrots look orange, grapes look green and cucumbers look a darker green. Cauliflower looks white.</p>
<p>At a colour rendering index of 70, the full spectrum of colour, tones and shades are not seen very well; tomatoes, capsicums and applies look orange; carrots look yellow, grapes look green-blue and cucumbers look a darker green-blue. Cauliflower looks a pale white-green.

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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