Light is one of the family of electromagnetic waves ranging from the longest of radio waves to cosmic X-Rays. All electromagnetic waves have a wavelength and for visible light this is from about 400 to 700 nano-metres (a nanometer, nm, is equal to one thousand-millionth of a metre, 10-9 ).


The Electromagnetic Spectrum
Electromagnetic Spectrum
Daylight contains all the wavelengths in approximately equal amounts.

The human eye sees this as white light.


The Light Bulb (The GLS [General Lighting Service] Lamp)
GLS Lamp

Voltage applied to the filament heats it up to white hot which produces light. The filament is made from a fine coil of tungsten wire which is then coiled again (the 'coiled coil'). This reduces heat losses and gives up to 20% more light.

Life of a lamp depends on evaporation of the filament. Surrounding the filament with a vacuum allows it to operate at a high temperature, but will not reduce evaporation. Filling the bulb with a high purity mixture of argon and nitrogen allows high temperature operation as well as reducing evaporation.

GLS lamps come in three main finishes;

  • Clear
  • Pearl/opal (the glass is lightly acid etched to soften the light)
  • White (the glass has an internal coating of silica that completely diffuses the light over the whole bulb surface)


Mains powered GLS lamps have an integral fuse to protect the lamp and prevent explosions.

Tungsten filament lamps are available ranging from about ½ Watt (as used in a torch/flash-lamp) to 5 Watts (car side lights) up to 150 Watts (warehouse flood lighting).

Tubular filament lamps (usually about 60 Watts) are popular for bathroom and bedroom furniture illumination.


R-type lamp For display purposes a range of general purpose blown-glass reflector lamps are available. These bulbs have the filament set at the focus of a parabolic mirror.

Types are identified as Rxx, or ROxx (where xx = lamp diameter in mm).

The front lens of the bulb may be either strongly or lightly patterned to diffuse or focus the light output depending on the type of display illumination required. They may also be coloured blue, green, red or yellow.
Display lighting in shop windows often use the Crown Mirrored bulb, in which the top half of the glass bulb is coated with a silvered finish.

This bulb is designed to be fitted in a saucer-shaped reflector of about 25cm (10”) diameter.
Mirror crown lamp
PAR lamp Reflector lamps for exterior use (e.g. flood or spot lighting for security purposes) are made from sections of borosylicate glass which are pressed and welded together.

These are known as PARxx (Parabolic Aluminised Reflector) types, where xx = lamp diameter in eighths of an inch, e.g. a PAR38 lamp has a front face diameter of 4¾”.

GLS Craft Light (daylight simulation) lamp. The transparent blue filter applied to the glass envelope absorbs the yellow part of the spectrum to provide simulated daylight.

Craft lights are available in GLS, Candle, Pygmy, Golf Ball and Reflector styles.

GLS - Craft light (daylight) lamp


Halogen Lighting

The life of any filament lamp is determined by the evaporation of the filament. The addition of a very small amount of halogen, usually bromine or iodine, to the normal argon gas in the bulb reduces evaporation.

At the bulb wall where the temperature is about 300°C tungsten evaporated from the filament combines with the halogen.The resultant tungsten halide compound is carried back to the filament by normal convection currents.

The high temperature close to the filament separates the tungsten from the halide, and the halogen is free to repeat the cycle.

Because the bulb temperature needs to be at least 250°C it is usually made from quartz rather than glass.


Halogen lamp - capsule

Halogen lamp - linear


Tungsten Halogen lamps have a longer life, give more light and are much smaller than their conventional equivalents. Since there is little bulb blackening the colour of the light remains crisp, brilliant white for the life of the bulb.

Bulbs should not be directly handled. Because of the high operating temperature any contaminants on the bulb surface (e.g. natural oils from the skin) will cause localised surface cracking and eventually early failure of the quartz envelope.

Lamps are available in linear tube or capsule lamp versions and either mains powered or in a low voltage. When selecting a transformer always run it at the maximum rating wherever possible,
e.g. for a 50W lamp use a 50VA transformer, for four 50W lamps use a 200VA transformer, etc. Poor voltage regulation may cause premature lamp failure.


Halogen lamp - dichroic

In the dichroic reflector lamp about 66% of the heat produced by the lamp is dispersed by the reflector in the opposite direction to the light beam, resulting in a very cool light beam, but the back-side is very hot indeed!

Dichroic reflectors often have a glass cover incorporated into the front of the lamp which effectively eliminates UV-C radiation and greatly reduces UV-B. It is possible to have colour-tinted glass filter covers.

Power ratings are 10W, 20W, 35W, 50W, 100W, 250W with light beam-width is from 7° (spot) to 55° (flood).


Tubular Fluorescent Lamps  

A fluorescent lamp is a glass tube containing low pressure argon gas and a small amount of mercury. Electrical energy is used to excite the mercury gas molecules which produces ultra-violet light.

This UV light excites a phosphor powder coating on the inside of the tube. The powder fluoresces giving out visible light. Phosphors are powders (eg zinc sulphide) which are designed to phosphoresce at characteristic wavelengths (colours). Blends of phosphors produce different colours (eg Cool White, Warm White, Daylight, etc.).

By adding rare-earth minerals to the tube phosphors during manufacture can tailor the
light colour from subtle differences in white (northlight, cool white, warm white) to almost pure
primary colours (red, green, blue).


Fluorescent tube schematic To work efficently most tubes require the gas to be heated. This is done by passing an electric current through the electrodes (called cathodes) at each end of the tube. The heated cathodes each emit a cloud of electrons which ionises the gas in the tube.
The ‘starter’ controls the heating of the cathode and the exact moment when the mains power is connected to the tube. Once the gas is ionised it is the voltage difference between the ends of the tube (i.e. mains Live at one end, Neutral at the other) that strikes an arc in the gas which creates the light.


Tube Diameter Tube Power and Length
 T5 5/8” (16mm) diameter

 4W     6” (150mm)
 6W     9” (225mm)
 8W    12” (300mm)

 T8  1”  (26mm) diameter

 18W    2’ (600mm)
 30W    3’ (900mm)
 36W    4’ (1200mm)
 58W    5’ (1500mm)

 T12 1½” (38mm) diameter

 40W    4’ (1200mm)
 65W    5’ (1500mm)
 75W    6’ (1800mm)
 85W    8’ (2400mm)

(Note: The T-number is a measure of tube diameter in eighths of an inch)


Compact Fluorescent lamps (CFL)  
This family of lamps are marketed as ‘energy saving lamps’ and are designed to replace standard filament lamps. They work in a way similar to tubular fluorescent but have a very compact tube construction.

Compact Fluorescent Lamps

The International Lamp Coding System, (ILCOS) describes the square (2D), single-U (2L) and multi-U (4L) compact fluorescent tube shapes

They use an electronic control system which operates the lamp at a high frequency (about 32 kHz). This has the advantage of an almost instant start and flicker free illumination (‘normal’ fluorescent lights operate at 50 Hz - the frequency of the mains).

They produce useable levels of light 8 to 10 times longer than an equivalent filament lamp.


Tubular Cold Cathode Lamps  

These tubular lamps are similar to regular fluorescent tubes except that heated electrodes (cathodes) are no longer required.This is the origin of the name 'Cold Cathode'. As no bulky heater assemblies are used Cold Cathode lights produce end-to-end light without the usual dark end-region.

Recent advances in cold-cathode technology has permitted the manufacture of tubes from as short as 15 cm up to several meters. Applications range from illuminating the internal parts of a computer to architectural interior and exterior lighting.
In operation a power supply of about 400 VAC is needed which, to reduce the flicker effect, is operated at several kHz.


Gas Discharge Lamps  

The light comes from exciting a gas or vapour contained in the discharge tube. These lamps have poor colour rendering, but are very efficient and have a long life. The poor colour rendering can make it difficult to determine the real colour of an object illuminated by it.

There are two major families of discharge tubes, Mercury and Sodium.


Mercury lamps
The characteristic colour of the light output is blue-green.

warning sign Safety
Mercury lamps should NOT be operated if the outer glass bulb is broken. Dangerous radiations from the inner quartz discharge tube which are normally absorbed by the outer glass bulb will be released.


Sodium Lamps
There are two types of Sodium Lamps - Low Pressure (SOX) and High Pressure (SON)

Low pressure sodium lamps (SOX) give light which is virtually monochromatic, i.e. yellow light at one wavelength only. Colour rendering is very poor. Yellow and white objects look yellow, all other colours appear as various shades of grey and black. They are very efficient and are widely used for street lighting.
Technical Part:
The discharge tube is contained within a protective glass sleeve. The arc is normally started with neon/argon gas mixture which gives these lamps their characteristic red glow. The sodium eventually takes over the discharge and the light turns to yellow. Full brightness is achieved after about 15 mins.

High pressure sodium lamps (SON) have a wider spectral output with a corresponding improvement in the colour rendering properties. The light is still biased towards the yellow, but is very acceptable in general purpose applications and allows colours to be readily distinguished. Main applications are for city centre street lighting, floodlights and in industrial areas.
Technical Part:
The discharge tube in this lamp is made from sintered aluminium oxide which is able to withstand the chemical action of hot ionised sodium vapour.

warning sign
Metallic sodium burns violently when exposed to moisture. Each lamp is supplied with disposal instructions. A sound practice is to break the lamp(s) in a bucket in the open then pour on water from a distance using a hose. After a short while the residue may be disposed of as glass.


Lamp Type
Typical Application
 Mercury  MBF  Office
 Shop lighting
 Mercury-Metal Halide  MBFI  Floodlighting
 Road lighting
 Low Pressure Sodium  SOX  Road lighting
 High Pressure Sodium  SON  Industrial areas
 Sports arena
 Shopping precincts


Light Emitting Diode    

A Light Emitting Diode (LED) is manufactured from a mixture of semiconducting metals such as Gallium and Arsenide. Addition of other metals during manufacture will give a different colour of light. Recently intense blue and white LEDs have been developed and are being incorporated into the latest designs for indicators and general illumination.

Infra-red LEDs are used widely in electronics as sensors, motion detectors, remote control handsets for TV and VCR.

Due to an increasing shortage of tungsten for use as lamp filaments many vehicle manufacturers are now using high-intensity LED clusters for rear/stop (red) and turn (yellow/orange) indicators.

LEDS - multi-colours
Typical LED colours

The LED works within a limited range of DC voltage and current. It is essential these limits are not exceeded otherwise the LED will be destroyed.

The LED is polarity conscious. The anode is signified by the longer lead and this should always be more positive than the voltage on the cathode.


It is essential that a resistor (RLED) is put in series with the LED to limit the current flowing in the circuit to a safe level.

Normal LED current (ILED) is 20mA - Low Current devices usually operate at 2mA.

Typical operating voltages (VLED) are:

  • Red = 1.6V
  • Green/Yellow = 2V
  • White/Blue = depends on manufacturer... check spec sheets.
LED connections and electronic symbol

To calculate RLED when operating the LED on DC use the equation:

LED DC power circuit

Use this equation to calculate series resistor for DC

To calculate RLED when operating the LED on AC wire up an additional rectifier diode across the LED as shown then use the equation:

LED AC power circuit


Use this equation to calculate series resistor for AC


  • ILED is the current flowing through the LED
  • VLED is the voltage across the LED
  • VSUPPLY (or VAC) is the supply voltage


A useful technical link about LED's is here and about High Power LED's is here


Laser Light Sources


Laser Warning sign

A Laser generates light at one specific frequency. This is known as 'coherent light'. The stable frequency (wavelength) of the light permits straightforward processing and measurement. Laser light systems are widely used in telecommunications, time and distance measurement, communications and many other applications.

Laser pointers manufactured in the Far-East generate light at 650 to 670 nm, which is in the red region of the visible spectrum.

Whatever the power of the laser it is dangerous to stare into the beam as permanent eye damage will probably result.


CD players use a Laser-LED that operates in the invisible infrared part of the spectrum.
NEVER attempt to operate any kind of CD player or writer when the disc drawer is open.


Electroluminescent Lighting    

When a high voltage is applied to certain phosphorescent materials sandwiched between two electrical contacts light is emitted. This effect is known as electroluminescence. The colour of light depends upon the chemical make-up of the phosphors. At some expense to the brightness it is possible to introduce filters to change the colour of the light output.

The most common use for an electroluminescent light source is as a back-light in products such as the "Indiglo™" watch, mobile phone screens, calculators and other applications where the user is required to read information displayed on a screen when ambient lighting is poor.


EL display panel
Electroluminescent Panel
(move cursor over image)

In addition to the regular flat-panel form, a wire-like EL product is available. The construction consists of a central wire on to which the phosphors are bonded. The outer surface of the phosphor has several very thin wires wrapped helically along its length. The assembly is then encased in a flexible protective transparent outer sheath.
When the high voltage supply is connected between the inner and outer wires the phosphors glow. Several natural colours are available; cyan, green and blue. For otherr colours it is necessary to tint the outer sheath.

Electroluminescent wire
Electroluminescent Wire


Connecting up the EL Display

EL Driver circuit


An EL Driver module contains the necessary electronics to change the low voltage from a battery (typically 3V or 9V or 12V) to the high voltage, high frequency AC required to drive the EL Panel/Wire efficiently. The module may already incorporate the on-off switch.

Wire up your circuit as shown, taking care to avoid short circuits and insulate all AC wiring to prevent electric shock hazard (the unit probably won't kill you, but you may get a nasty suprise if you touch a live AC wire!!)


Some wise precautions when dealing with EL:

  • In normal operation an AC supply of approximately 400V at a frequency of about 1500Hz is required. The life of the EL-product is dramatically shortened if a DC supply is used.
  • As ALL electroluminescent phosphors absorb atmospheric moisture it is essential to adequately seal all possible entry points to prevent premature failure of the product. Use heat-shrink tubing.
  • Avoid bending the EL material too sharply. The phosphors may crack resulting in dark lines and spots on the illuminated surface.


Lamp Connections  

A high degree in standardisation of lamp connectors has been achieved.

The style of connector can be described in two ways:
  i)  by a description of the physical shape, or
  ii) by using the internationally agreed Designation Code.

Some of the most common Designators:
 B  Bayonet (often called Bayonet Cap)  s = one contact

 d = two contacts

 t = three contacts

 q = four contacts

 p = five contacts
 BA  Bayonet (for automobile use)
 SBC  Small Bayonet Cap
 MBC  Miniature Bayonet Cap
 E  Screw Thread (often called Edison Screw)
 GES  Goliath Edison Screw
 SES  Small Edison Screw
 LES  Lilliput Edison Screw
 G  Connector with two or more contacts

Technical Stuff:
Each letter is followed by a number which represents the major dimension of the cap (usually the diameter).

After the number will be a lower case letter which shows the number of electrical contacts (excluding the connector body if this is used as a contact).

Edison screw cap Bayonet cap

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