Types of lamps

Types of lamps

(i) Incandescent (GLS)

The Incandescent lamp is the oldest electric light source still in general use. It is also the most varied as regards types. It can be found in almost any application, especially where comparatively small light packages are required and where simplicity and compactness are favoured.

 Filament Lamp

(1) Glass bulb (or “envelope”).
(2) Low pressure inert gas.
(3) Tungsten filament.
(4) Contact wire (goes to foot).
(5) Contact wire (goes to base).
(6) Support wires.
(7) Glass mount/support.
(8) Base contact wire.
(9) Screw threads.
(10) Isolation.
(11) Electrical foot contact.

(A) The main characteristics are

Efficacy

It defines light output per unit of power input (lumens/watt).
The following comparison illustrates this point:

                            Main characteristics of incandescent lamp

Incandescent Lamp Advantages

(1) Simple to use - direct connection into socket.
(2) Lowest initial lamp cost.
(3) Immediate starting and re-starting - no warm-up or cool down required.
(4) Excellent optical control - concentrated light source is easiest to direct or focus.
(5) Easiest to dim - simple variable resistor circuitry may be all that is required.
(6) Wide design flexibility - variety of styles, outputs, and colours fill nearly every need.
(7) Output not affected by operation over a wide range of ambient temperature.
(8) Available in wattage ratings from 10 to 100W.

Incandescent Lamp Disadvantages

(1) Sensitive to shock and vibration.
(2) High overall operating cost - low efficacy and short life.
(3) Sensitive to voltage variations
(4) Sensitive to thermal shock - high bulb surface temperature requires that the lamp be protected from moisture. Exceptions are hard glass bulbs and low wattage lamps (less than l0W). Lowest efficacy - all other lamp types surpass incandescent performance by a large margin.

(ii) Halogen Lamps:

A halogen lamp is a special kind of incandescent lamp. The light output is more consistent than a standard incandescent lamp and the life is longer. Size is smaller because it is important for the halogen cycle to have a high bulb wall temperature, which requires quartz or hard glass to be used. Better beam control is possible because of the small source size. Basic Halogen Lamp Types the common types of halogen lamps are:

(1) Linear (sometimes called double-ended)
(2) Single-ended
(3) Capsule (single-ended but no outer bulb)
(4) PAR (capsule contained in PAR shape bulb) Used for gardens or stage lighting.
Also known as spot or reflector lamps Lens
(5) Low Voltage Reflector (Precise lamps)

(A) Features of the Halogen Lamps:

Luminous Efficacy:
Luminous efficacy increases with higher tungsten temperature. Using Xenon (larger atoms) the temperature can be raised to increase the luminous efficacy by 5%-10% and colour temperature by about 100 degrees Kelvin. Xenon can only be used in low voltage lamps because the lower ionizing energy of Xenon would lead to an electrical discharge with higher voltages.

(iii) Fluorescent Lamps:

The fluorescent lamp is commonly used. It has hundreds of sizes, wattage, colours, voltages and specific application designs the typical fluorescent lamp is a hot cathode type, consisting of a sealed glass tube containing a mixture of inert gas and mercury vapour. The cathode causes a mercury arc to form inside the tube. This arc produces ultraviolet (UV) light, which is not visible to the naked eye. The UV light strikes the phosphors coating that is inside the tube which will fluoresce producing visible light. Output can be controlled by changing the type of phosphors and the lamp colour. The fluorescent lamp requires ballast in its circuit. Its purpose it limits the current in the circuit, without the ballast the lamp would draw excessive current, and the fuse or circuit breaker would open. The lamp also consists of a starter, which acts as switch.

 Fluorescent lamps

(A) The life of fluorescent lamps

Fluorescent lamps have outstandingly long life. This life is affected by the number of times the lamp is turned on and off since switching tends to wear out the cathode. An average fluorescent lamp burned continuously will last about 30000hours with three burning hours per start, it will last about 12000hours. Most users replace lamps when they reach about 75% of burn out life because the light output has dropped at that point to about two third.

(B) Power Factor of Fluorescent Lamp

Ordinary incandescent lamps have a power factor of 100%. A fluorescent lamp connected to a circuit has a power factor of somewhere between 50% and 65% to improve power factor.

(C) Advantages and Disadvantages of Fluorescent Lamps

    Advantages and Disadvantages of Fluorescent Lamps

(D) Compact Fluorescent

Compact fluorescent lamps resulted from research into energy saving lighting. The goal was to develop smaller, more efficient light sources with greater lumen output per watt. One solution was to re-design the fluorescent lamp and its cap. Two basic designs have emerged:

(1) Biaxial
(2) Square plane

The internal construction and function of all variants is very similar to linear (straight) fluorescent lamps.

(iv) Discharge Lamps:

Gas discharge lamps are used in virtually all areas of modern lighting.
As for fluorescent lamps the electrical energy is transformed into radiated energy by the discharge through a gas/metal vapour, the spectral distribution is dependent on the chemical and the pressure/temperature of the discharge.

(A) Types of Discharge Lamps

(1) Low Pressure Sodium
(2) High Pressure Sodium
(3) High Pressure Mercury
(4) Metal Halide

 OSRAM clear Mercury vapour lamp HQA 80 Watt.

 OSRAM colour corrected Mercury vapour lamp HQL 80 

The choice of colours, size and rating is greater for Metal Halide than any other lamp type Some Metal Halide lamps use a third electrode for starting, but other, especially the smaller display lamps, require a high voltage ignition pulse.
The halides act in a similar manner to the tungsten halogen cycle. As the temperature increases there is disassociation of the halide compound releasing the metal into the arc. The halides prevent the quartz wall getting attacked by the alkali metals.