The Function of Light


How we see colour:-

When light falls on an object, the surface absorbs some of the
colours and reflects back the rest. Different surfaces have different
reflective capabilities.
A Yellow object reflects back yellow light, a green object absorbs all
colour except green. Black surfaces absorb all colours, while white
reflects them all.

Light has two distinct properties colour appearance and colour

Colour Appearance

The colour appearance of light – whether it is “cool” or “warm”
is usually expressed in terms of its colour temperature. Colour
temperature is measure in degrees (Kelvin). The higher the
temperature the cooler the light, therefore the lowest colour
temperature achieves the warmest lighting effect. A candle’s
colour temperature achieves the warmest lighting effect. A
candle’s colour temperature is 2000K (Kelvin) but it offers a warm
yellow light, whereas some fluorescents are between 4000-6000K
(kelvin) and generate a very cool light

Colour Rendering

The colour rendering refers to the appearance given to an object
by the light source. This is an important consideration in interior
environments given that most light is reflected back off the
surrounding objects and surfaces. Reflectance relates to how much
light is reflected by an object or surface.

Tip: Although fluorescent may appear to be a cool white colour
(similar to sunlight) it tends to produce a bland effect (overall light)
which is why fluorescent is rarely used in restaurants.

How colour and surfaces affect light

• Light colours, because of reflection spread light throughout the
• Semi-gloss paint reflects more light than matt paint
• A room with dark colours will require more light than normally
• A room with lights colours can be effectively illuminated with
less light than normally recommended.

Tip: The room colours will determine the type of lighting solution

The following list outlines the recommended reflectance levels of
different surfaces / objects

Ceilings 70 – 90%

Walls 40 – 60%

Floors 20 – 40%

Worktops 30 – 50%

Cabinets 30 – 60%

Furniture 25 – 45%

Office Equipment 25 – 45%

Timber 20 – 30%

The typical reflectance levels of paints are:

Black 0 – 10%

White 80 - 90%

Pale Yellow 80%

Mustard 35%

Pastel Colours 70%

Pale Blue or Green 70 – 85%

Dark Blue or Green 20 – 30%

Light Grey or Beige 25 – 35%

Orange 20 – 25%

Red 20 – 25%

Dark Red 10 – 15%

Lighting Controls - Dimmers

Lighting dimmers add flexibility to your lighting. There are many
types available from sophisticated dimming systems that allow you to
automatically present lighting effects.

Dimmers can either be leading or trailing edge.

Leading Edge dimmers are the most common (and economical). They
remove the beginning of the incoming AC mains power to control the
light output. Trailing edge dimmers remove the trailing section of the
incoming supply voltage to control the power.

The correct size dimmer must be selected. To calculate the intended
load on the dimmer, multiply the wattage by the number of lamps/
fittings. It is recommended that you buy a dimmer with a larger capacity
than required.

Example: 50W x 6 = 300W, therefore a dimmer with a rating of at least
300W is required, but better to use a 400W.

All standard filament lamps (incandescent, dichroic, linear halogen) can
be operated by a standard household dimmer.

LED’S required to dim will need to have a compatible dimmer module.

Let’s Re-Cap

• Accent Lighting - Light that focuses attention on an object or
• Ambient Lighting – Light that provides general illumination in a room
• Colour rendering Index – The CRI indicates how a light source affects
the appearance of colours. On the 1 to 100 scale, 100 indicates no
colour shift. Objects may look unnatural under lights with a low CRI
• Colour Temperature – Measurement of the colour warmth of light
source, measured on the Kelvin scale. Sources below 3200 K are
usually considered warm white; those above 4000 K are considered
• Glare - Excessively harsh or bright light.
• Intensity - the amount of light emitted by a source and the amount
that ultimately reaches an object or surface.
• LED - Light-emitting diode, a small low power light source.
• Lumen – A measure of light output, one lumen of light uniformly
distributed over 1 square foot of surface provides 1 foot-candle of
• Reflectivity – the amount of light that an object reflects is
determined by its reflectivity, a technical terms for its lightness.
• Task Lighting – Illumination on a work area

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