Light the Lights - Comparing options for domestic lighting

Thursday, April 04, 2013


There is a diverse range of lighting fixtures and lamps available in the domestic market where each lamp has its own advantages and disadvantages. The diagram below shows some of the basic lighting technologies which are popular in the local market for savvy. But this article mainly focuses on domestic lamps, their advantages and disadvantages and how they can be utilized optimally to serve your requirements.

Basic Lighting Technologies
Terminology

Incandescent Lamps

Incandescent Lamp
The incandescent lamp is a very commonly used lamp type in household applications. If stated in simple terms, the basic operating mechanism of an incandescent lamp is passing of an electric current through a tungsten spiral which heats up to such a level as to emit light.

 Advantages
  • Inexpensive 
  • Dimmable
    • A dimmer, which is generally a variable resistor, installed in series with the lamp, renders the capability of controlling the current through the lamp and thereby, the capability of dimming it.
  • Great Colour Rendering Capability (100 – the maximum possible)
    • Due to the extensive colour rendering capability, colours of objects in the illuminated area can be viewed realistically. Therefore, incandescent lamps becomes the ideal choice for places where differentiation of colours of the objects is of greater concern, such as in jewellery shops. 
  • No mercury (environmental friendly)
    • Unlike CFLs or Fluorescent Tubes, Incandescent lamps do not contain mercury. Therefore, they do not support environmental pollution or poisoning due to mercury, during disposal of the lamp.
  • Fast switching
    • Due to the absence of warm up time or pre heating time, incandescent lamp can be turned on instantly to produce full brightness. Further, frequent switching does not affect the lifetime of the lamp. Thus, incandescent lamps can be used where fast switching and frequent switching is a necessity.
Disadvantages
  • Low luminous efficacy (8 to 24 lm/W)
    • The notable disadvantage is the low luminous efficacy of the incandescent lamp which ranks this lamp in the tier of low efficiency. 
  • Lifetime of this lamp is short due to evaporation of the Tungsten filament, typically after 750 to 1000 hrs

Tungsten Halogen


Tungsten Halogen Lamp
The Tungsten Halogen is an advanced form of the Incandescent lamp. Similar to the Incandescent lamp, the filament of the Tungsten Halogen lamp is made of Tungsten metal. But the gas filled inside the Tungsten Halogen bulb is a pressurized halogen, usually Iodine or Bromine, under a pressure of 7 to 8 atm.

To withstand the high pressure involved, the glass bulb is made stronger and thicker than in a conventional incandescent lamp. The halogen gas molecules are capable of capturing the evaporated tungsten atoms from the heated tungsten filament and redepositing them back on the filament. This halogen cycle enables the filament to reach higher temperatures and to produce more luminous flux. Additionally, it increases the lifetime of the lamp.

Tungsten Halogen lamps are used in household lighting, especially as spot lights. They are also used in automobile lamps.

Tungsten Halogen lamps possess advantages and disadvantages similar to incandescent lamps.

Advantages
  • Small and light in weight
  • Dimmable
  • Great Colour Rendering Capability (100)
  • No mercury (environmental friendly)
  • Fast switching  
  • Higher life time than Incandescent lamps as the Tungsten-Halogen cycle reduces the evaporation of the filament. Typical lifetime is 2000-2500 hrs.  
Disadvantages
  • Low luminous efficacy (12 - 35 lm/W)

 Fluorescent Tube Lamp

Fluorescent Tube Lamp
[Photo: http://www.edisontechcenter.org/lighting/Fluorescent/PreheatFluorescentLabeled80.jpg]

The working principle of fluorescent lamp is different from filament lamps.

The electrodes at the two ends of the lamp are heated up so that they start to emit electrons. Emission of electrons is governed by the ballast and the starter. These electrons collide with the atoms of argon (noble gas) near the electrodes of the tube and ionize them. This starts an avalanche ionization process throughout the lamp, creating a path for the current to flow through the lamp. Subsequently the electrons get the opportunity to easily collide with the vaporized mercury atoms. During these collisions, ultra-violet (uv) photons are released. When these photons meet the phosphorous layer of the tube, visible light is emitted.

Fluorescent tubes are very useful in efficient lighting of houses and offices. They are ideal for areas where diffused lighting is necessary rather than focused lighting.

Advantages
  • Higher luminous efficacy (80 – 100 lm/W)
  • Long life - typically 20,000 hrs
  • Diffused light - To places where diffused light is necessary
  • Fairly good CRI value (75-85)

Disadvantages
  • Cannot dim with a series variable resistor.
  • Switching frequency and voltage variations directly affect the life time
    • Higher the switching frequency, lower the useful lifetime of the lamp. Higher the voltage increments than the rated voltage, lower the useful lifetime of the lamp. (Note: useful lifetime is the time period until the luminous flux output of the lamp drops down to 70% of the rated luminous flux output.)
  • Not environmental friendly due to mercury content.
  • Cannot turn on quickly as it needs a warm up time of few seconds.

 Compact Fluorescent Lamps (CFL)
Compact Fluorescent Lamp (CFL)
The CFLs have a similar working principle to that of the fluorescent tubes. CFLs normally come with electronic ballasts integrated to the lamps themselves. They are designed to fit in to the holders generally used for incandescent lamps, making it easier for the consumers to replace incandescent lamps with CFLs without any special changes to the existing wiring arrangements.

CFLs are an energy efficient substitute for incandescent lamps in situations where colour rendering capability is not vital.

Advantages
  • High luminous efficacy (50 to 85 lm/W)
    • It should be noted that the luminous efficacy of CFL is lower than the fluorescent tube but greater than the incandescent lamps.
  • Longer life - typically 6,000 to 12,000 hrs
  • Fairly good CRI value (80)
Disadvantages
  • Not dimmable with a series variable resistor.
  • Mercury content pollutes nature at disposal
  • Switching frequency affects the lamp adversely


LED (Light Emitting Diode)
LED (Light Emitting Diode)
[http://www.edisontechcenter.org/lighting/LED/ScrewInBulbLEDarray326.jpg]
LEDs are type of semiconductor diodes, which emits light when they are forward biased. The mechanism of light emitting has to be explained at the atomic level. But that process can be explained in simpler terms.

An electron releases energy when it drops from a higher orbital to a lower one. This energy is released in the form of a photon. A greater energy drop releases a higher-energy photon, which is characterized by a higher frequency.

Free electrons moving across a diode can fall into empty holes from the P-type layer. This involves a drop from the conduction band to a lower orbital, so the electrons release energy in the form of photons. This happens in any diode, but you can only see the photons when the diode is composed of certain material.

Visible light-emitting diodes (VLEDs) are made of materials characterized by a wider gap between the conduction band and the lower orbitals. The size of the gap determines the frequency of the photon. In other words, it determines the color of the light.

Lamps made using LEDs are available in the market and they have a much higher luminous efficacy; thereby saving a lot of energy.

Advantages
  • High lifetime - typically 100,000 hrs
  • High luminous efficacy (150 lm/W)
  • No mercury content
  • Fairly good CRI value (70)
  • Dimmable using a PWM (Pulse Width Modulation) circuit.
  • Durable 
Disadvantages
  • High heat dissipation causes the need of heat sinks making the lamp bulky and costly.

References

Article By: Supun De Silva

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