Principles of Artificial Lighting

PRINCIPLES OF ARTIFICIAL LIGHTING

Light can be produced by nature or by humans. "Artificial" light is typically produced by lighting systems that transform electrical energy into light.

Nearly all lighting systems use electrical current or through

1. Categories of light

There are '3' categories of light. They are

(a) Direct

(b) Reflected

(c) Indirect

 

(a) Direct

Direct light is light travelling unimpeded from the light source to the subject. It is not filtered, diffused, reflected or altered. Direct light is like the sun light on a clear day.

The effect of extensive use of lighting is direct, impressive and active both ambient light and artificial light.

(b) Reflected

Second type is semidirect (or) reflected lighting. It is visible but brightness is less.

Reflected light is light proceeding from a light source, reflected by a remote surface and incident onto an object. Light reflected into an umbrella with a black backing is an example of reflected light.

Light can also be reflected off a white wall or a silver card and directed towards a subject. Reflected light is less directional than an unimpeded source light.

(c) Indirect light

The third type is indirect lighting. It is invisible but it falls on working area.

The combination of 3 types of lighting can be used on any lighting systems. All the methods give pain to the eyes, if proper lighting is not set in. Table lamp is useful but it is harmful to the eyes.

 

Artificial light sources

The most common five artificial light sources are as follows:

1. Incandescent lamp

2. Fluorescent tube

3. Compact Fluorescent Lamp (CFL)

4. Discharge lamp

5. Light Emitting Diode (LED)

 

1. Incandescent lamp

Until recently the most common electric light source is an incandescent lamp.

This lamp consists of a filament made up of fine tungsten wire fixed inside the glass support produces light as shown in fig. 3.17.

A larger variety of shapes, sizes and power as well as different colour ranges is available.

Typical lamps for household use range from 40 to 100 W. The light output of 420 to 1360 lm is produced at the typical lamp efficiency of about 12%.

This is still widely used, although it has relatively low energy efficiency. It leads to replacement by other more efficient lamps such as the CFL.

 

2. Fluorescent lamp

Fluorescent lamp is the main form of lighting for offices and commercial buildings. It uses fluorescence to produce visible light.

It is a gas discharge lamp. It is formed in a long thin glass cylinder. This lamp has contacts at either end that secure them to the fitting (or luminaire) and provide the electrical connection.

The tube contains mercury vapour at low pressure. The inner wall of the glass is coated with a phosphor that reacts to ultra-violet radiation.

When electricity is passed through the vapour, it emits UV radiation that is converted by the phosphor to visible light. (Fig. 3.18).

3. Compact Fluorescent Lamp (CFL)

The Compact Fluorescent Lamp (CFL), is a fluorescent lamp and it is designed as a more efficient replacement for incandescent lamp. It can be used in many light fittings designed for incandescent lamps (Fig. 3.19a & b). It works on the same principle as that of fluorescent lamp.

 

4. Discharge Lamp

In discharge lamp, the light is produced by the passage of an electric current through a gas or vapour as shown in fig. 3.20.

The different metals and filler gasses can be used to provide a range of colour and brightness. (Fig. 3.20)

The discharge lamps provide high luminous efficacy combined with long life.

 

5. Light Emitting Diode (LED)

LEDs use semiconductors to convert electrical energy directly into light. They are only recently becoming available as a light source for lighting purposes. They are highly efficient and long lasting. (Fig. 3.21)

• A light-emitting diode (LED) is a two-lead semiconductor light source. It is a p-n junction diode that emits light when activated.

• When a suitable voltage is applied to the leads, electrons are able to recombine with holes within the device, releasing energy in the form of photons.

LED torches are becoming very popular, as they provide a far longer battery life than other types of light source.

 

Forms of Artificial lighting

There are two forms of artificial lighting. They are beau od 89 29

1. Indoor lighting

2. Outdoor lighting

 

1. Indoor Lighting

Indoor lighting is usually accomplished using light fixtures, and it is a key part of interior design.

Luminaire is a device that distributes filters or transforms the light emitted from one or more lamps. The luminaire includes all the parts necessary fo for fixing and protecting the  lamps.

The basic physical principles used in optical luminaire are reflection, absorption, transmission and refraction.

Types of Light Fixtures

There are five basic types of light fixtures based on function.

(a) Ambient (general lighting)

(b) Task

(c) Accent

(d) Informational lighting/Guidance Lighting

(e) Decorative lighting

 

 (a) Ambient

Ambient lighting provides an area with overall illumination. Also it is known as general lighting and it radiates a comfortable level of brightness without glare.

Ambient lighting is often provided by traditional pendant type fixtures, down lights, chandeliers, or ceiling mounted fixtures, etc.

The general decor and respect of the room will affect the amount of general lighting required. Having a central source of ambient light in all rooms is fundamental to a good lighting

 

(b) Task Lighting

Task lighting, or directional lighting, is aimed at a specific task. It provides sufficient light on to perform a task that requires more re light than the ambient fixtures.

It can be provided by recessed and track lighting, pendant lighting under cabinet lighting and desk lamps (Fig 3.23)

 

(c) Accent Lighting eme nut ai or Ils ai digil Jasidms

Accent lighting is also a sort of a directional lighting that adds drama to a place by creating visual interest. As part of an interior design scheme, it is used to draw the eye to houseplants, paintings, sculptures and other prized possessions.

It can also be used to highlight the texture of a brick or stone wall, window treatments or outdoor landscaping (Fig 3.24).

 

(d) Informational Lighting (Guidance Lighting)

It is designed to see our way safely. The light in our closet, the light by our door bell and night lights, as well as path lighting and motion lights, are all good examples of informational lighting.

Figure 3.25 is a typical night light with a photosensor. Informational lighting can be beautiful as well as functional, and can create dramatic statements. Lights inset on stairs can create pathways that enhance architecture, while outdoor informational lighting can create shadows and texture.

 

(e) Decorative Lighting

Light strips, pendants, chandeliers, and sconces are all examples of light fixtures that draw attention to themselves and add character to the place being lighted. Many are used for general lighting (Fig. 3.26).