Introduction
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 ).

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)

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.

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.

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.

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).

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).

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.

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.

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.

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.

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.

Laser Light Sources

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.

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.

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.

Connecting up the EL Display

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.

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.