Low energy lighting considerations – Part 1 of 3

One of the prime areas to consider in any refurbishment is the lighting. Lighting can make or break the appearance of a space. The lighting colour (meaning  mostly the warmth of the ‘white’ light), brightness, placement, directionality and controls are all significant matters. Each of these will vary from room type to room type and in some cases from a dull daytime when lighting is needed to after dark.

Lighting types

The majority of the fittings are fitted with incandescent bulbs. As is well known these are energy eaters and should be replaced by lower energy lamps, but what type or types. Let’s look at the overall picture before getting down to individual details.

This table shows the three main types of light source commonly found in 220V equipped dwellings and their key characteristics. It shows the following…

  • The rated output in lumens per watt of energy
  • The percentage efficiency of the lamp type
  • The rated life expectancy
Type Description Lumens per Watt Efficiency % Typical Life (hours)
Incandescent 60 to 100W bulb 14 to 17 2.3 1,000
Quartz halogen 24 3.5 2,000
Compact fluorescent 60 9 10,000
Fluorescent tube T8 or T5 90 13 25,000
LED White, inc PSU 40 to 100 6 to 13 40,000

Understanding the lighting type parameters

Tables are great at allowing you to compare different lighting types at a glance. However, care must be taken as the comparisons are not as straightforward as might appear. Firstly, the figures shown are not from a consistent source, I have not been able to find one that does a good side by side covering all types, and so the values quoted are an interpolated values from various figures found from manufacturers, specifiers and academic sources. Additionally the figures for ‘Life’ have to be defined differently because of the different failure modes, see the detailed discussion below.

Putting the table another way makes one conclusion abundantly clear. In this case we take the standard 60W lamp, the most common in current use, and adjust the other types to provide the same light output. Costs are based on electricity at £0.13 per Kwh

Type Description Lumens output Cost per 1,000 hrs
Incandescent 60 W bulb 800 7.80
Quartz halogen 33 W 800 4.30
Compact fluorescent 13 W 800 1.69
Fluorescent tube T8 or T5 @ 9 W 800 1.17
LED White, 10W 800 1.30

From this it is abundantly clear that running costs will be dramatically reduced by replacing incandescent (normal or halogen) lamps with any of the alternatives.

Chosing the lamp rating

If you are using the new lamp in a simple replacement situation then the illumination required can be calculated simply from the relative efficiencies of the two lamp types. The table below illustrates this simple relationship.

Type Rating 1 Rating 2
Incandescent 60 W bulb 100 W bulb
Quartz halogen 33 W 60W
Compact fluorescent 13 W 23W
Fluorescent tube T8 or T5 @ 9 W 15W
LED White, 10W 17W

Compact fluorescent can be considered almost a direct ‘plug-in’ replacement for a standard incandescent lamp and so the above is a reasonable set of figures when using the same luminaires. However the lighting patters from fluorescent tubes and LEDs are different and so the figures must be taken as an approximation because the light distribution will be different.

It is time to be imaginative with your new lighting setup!

For a more detailed look at the types of lighting see Part 2.

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