Home Lighting

Incandescent Lamps

The most common “traditional” type of light bulbs used in most homes are standard incandescent globes.  These emit radiation evenly and continuously over a range of frequencies far larger than is visible to our eyes.  A considerable amount of energy is thus wasted because we can’t see most of the radiation being emitted.  Incandescent lighting also gives off a large amount of heat as a consequence of the large amount of energy radiated in the infrared spectrum.  Halogen lighting is one of the most power hungry types of incandescent lighting because the light emitting filament is heated to extremely high temperatures.  Incandescent lighting is very similar in nature to the light from the sun whose radiation also covers a very broad spectrum of frequencies and is even and continuous across the range.  Incandescent lighting thus appears more “natural” to most people.  Typical incandescent bulbs for home use require 40-100W of power to operate, but halogen bulbs can have power ratings of 300-500W!

A particularly problematic incandescent lamp when it comes to energy saving is the ubiquitous 50W halogen downlighter.  They have the following drawbacks:

  • A single downlighter doesn’t fill a room with light.  Its light is concentrated in a narrow bean shining straight downwards.  This means a large number of lights have to be used to get an even light distribution in big rooms.  At 50 watts per downlighter, that quickly adds up to a large load, much larger than is necessary.
  • Halogen lights are very inefficient.  The bulk of the energy consumed is given off as heat.  Apart from the waste of energy, all that heat can cause problems.  Small enclosed rooms such as bathrooms, that need the lights on during the day, can become very hot in summer.  It may even become necessary to add additional airconditioning just due to the lights.  The heat given off by each downlighter also tends to eventually discolour the ceiling paint work.
  • Once all the holes have been cut in the ceiling it becomes impractical to convert to other more efficient light fittings.  There are CFL and LED downlighter alternatives available that will fit into the downlighter fittings, but they are quite expensive in comparison, especially if a large number are required.

So 50W halogen downlighters are a very bad choice of lighting for any building from an energy efficiency point of view.  If you are building from scratch, then you should avoid them at all costs.  If you already have them, consider just switching them off and fitting T5 luminairs in those rooms instead. If they are required for aesthetical reasons, then you should keep their number to an absolute minimum, and consider LED or CFL alternatives.


Fluorescent Lighting

This is one of the most efficient forms of lighting currently in domestic use.  Fluorescent lights emit high amounts of light for a given amount of electricity consumed (they use about one sixth of the power of an incandescent bulb to produce the same amount of light).  The two most popular types are the older “strip or tube lighting”, and the modern small “energy saver” bulbs which last far longer than incandescent bulbs (about six times longer than normal incandescent bulbs).  Fluorescent bulbs don’t emit light evenly at all frequencies (colours) across the visible spectrum the way incandescent lights do.  Light is simultaneously emitted only in three or four distinct narrow bands of colour which your eye combines into one colour.  This can be problematic when illuminating certain coloured objects.   This is because when you look at an object, you see the light reflected off its surface.  Objects appear to be different colours because they only reflect a specific subset of frequencies of light that strike their surface, all the rest is absorbed.  If the light source illuminating an object does not emit the frequencies that that object reflects, then it will appear dim or indistinct under that lighting to your eyes.  Another problem which affects older types of fluorescent lighting is they flicker quite distinctly.  Some people may find fluorescent lighting irritating either because they don’t seem to have a “natural” colour or because they flicker.   Fluorescent bulbs use 8-40W of power.

The most cost effective form of  fluorescent lighting are T5 tubes.  The designation T5 relates to the size of the tube.  T5 tubes are five eighths of an inch in diameter.  They are easy to distinguish because they are much thinner than the older generation fluorescent tubes.

T5 fluorescent bulbs produce up to 100 lumens per watt, while being relatively inexpensive.  One can typically expect about a 40% saving by converting from the older T8 tubes.

Unfortunately T5 tubes don’t fit into T8 fittings. An adapter is required if you don’t wish to replace the the older light fittings.  Most adapters include a built in electronic ballast.  Electronic ballasts are far more efficient and longer lasting than traditional magnetic ballasts used for older fluorescent tubes.

Light Emitting Diodes (LED’s)

Modern LED’s are becoming more and more powerful and are fast approaching the point where they can be used in normal domestic lighting applications.  The main draw card of LED’s is their very long life.  They typically last almost ten times longer than energy saver fluorescent globes.  LED’s also suffer from uneven emission of light across the visible range.  While they tend to emit light at all frequencies in the visual spectrum, they do so very unevenly with a typical large peak at the blue end of the spectrum and a second lesser peak at the yellow/red part of the spectrum and a large dip between the two.  This results in the same problem as fluorescent lighting where certain coloured objects become difficult to see and the colour of the light appears unnatural and irritating to some people.  A single LED typically uses 1-3W of electrical power.

Surviving a Power Failure

The big problem with regards to domestic lighting is that you are literally left stumbling around in the dark when the power fails at night.  Even simple routine activities such as eating become a challenge.  One needs some form of alternative power source to provide light in at least the most commonly used rooms in the house if the mains power fails regularly.

Energy Saving Tips

Convert to low energy bulbs where ever practical.  Especially try and replace halogen bulbs where possible.  Low energy bulbs will also make it practical to use battery power as an alternative power source during power failures (incandescent bulbs use up the battery capacity six times faster). Switch off lighting when it is not required.  Day/night sensors can ensure that outside area lighting is switched off automatically when the ambient light becomes bright enough.  This can save some energy if you are not normally present to switch those lights off when that happens.  Only switch on lights in rooms when you are in them.

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