Artificial Light

Power Efficiency Guide

Ultimate Guide to Power Efficiency

Get Instant Access

All forms of energy use in buildings should be analysed, related to the different needs of individual architectural programmes, to see where savings can be made; for example in homes, the use of the natural source has always been paramount during the day, so few savings can be made. At night however, developments in lamp technology have produced significantly more efficient artificial light sources and this is an area where, due to the large quantity of residential property, significant savings have yet to be made; moreover major energy savings in the home are to be found in the means of heating and insulation. Table 4.1 illustrates the different aspects of the main types of lamp, providing comparisons to assist the architect in making his choice. The different factors identified are those of efficacy, lamp life and colour, but other factors that must also be considered are those of cost and control.

It can be seen from the column under 'Lamp efficiency' that the favourite domestic lamp - Incandescent Tungsten - has an efficiency of only 7-14 Lm/watt, whilst the compact fluorescent (CFC) has an efficiency of between 40-87 Lm/watt. At present the CFC lamps cannot be dimmed economically, but there are many areas in homes, where dimming is not a requirement, and with satisfactory colour (2700 K) there is no reason not to take advantage of their long life and lower wattage.

The newer generation of lower-energy lamps such as the compact and T-5 linear fluorescent lamps can in many cases replace less efficient incandescent sources, which can be four to eight times more efficient; they can also have more than eight times longer lamp life. Used in conjunction with high frequency electronic control gear further reductions of 20 per cent in power consumption or energy savings can be made.

To realize these gains they must relate not only to the lamp, but also to matching this with the the correct luminaire or light fitting. It is no use simply fitting energy-efficient lamps into inappropriate luminaires, resulting in unsatisfactory installations; furthermore an energy efficient scheme demands regular, consistent and informed maintenance. It may also be cost effective in large installations to operate a system of 'bulk replacement' of lamps after a specific period irrespective of how many lamps may have failed.

In buildings for industrial use, no doubt savings may be possible in a rigorous investigation of the plant required to run industrial processes; but the area most likely to result in the greatest savings is in building services, and the greatest of these will be in the lighting, where daylight is the key.

Table 4.1 List of artificial light sources (originally printed in Lit Environment, pp. 92)

Lamp

Type

Lamp

Circuit

Rated average

Wattages

Colour temp

CIE

CRI**

efficacy

efficacy

life (hr)z

(W)

(K)ยง

groups

(Lm/W)*

(Lm/W)

Incandescent

Tungsten Filament

7 to 14

7 to I4

I000

I5 to 500

2700

IA

99

HV Tung.

16 to 22

I6 to 22

2000

25 to 2000

2800 to 3100

IA

99

Halogen

LV Tung.

12 to 27

I0 to 25

2000 to 5000

5 to I50

2800 to 3100

IA

99

Halogen

High Intensity

Low pressure

100 to 200

85 to I66

I6 000

I8 to I80

N/A

N/A

N/A

discharge

sodium (SOX)

Fluorescent

Cold cathode

70

60

35 to 50000

23 to

2800 to 5000

IA

55 to 65

tubes

40 W/m

2

85 to 90

Halophosphate

32 to 86

I3 to 77

10000

I5 to I25

3000 to 6500

2 to 3

c. 50

(T8&TI2)

Triphosphor

75 to I04

CCG: 48 to 82

10000

4 to 80

2700 to 6500

IA& IB

85 to 98

(T5 & T8)

ECG: 71 to I04

20000

Compact

Triphosphor

40 to 87

CCG: 25 to 63

8000

5 to 80

2700 to 5400

IA/IB

85 to 98

fluorescent

ECG: 33 to 74

10000

IB

twinbased

Compact

Triphosphor

30 to 65

I5 000

3 to 23

2700

IB

85

twinbased

integral

ballast

Induction

Triphosphor

65 to 86

60 to 80

60000

55 to I50

2700 to 4000

IB

85

(fluorescent)

(service life)

High intensity

High pressure

75 to I50

60 to I40

28000

50 to I000

1900 to 2300

2&4

23 to 60

discharge

sodium (SON)

High intensity

High pressure

32 to 60

25 to 56

24000

50 to I000

3300 to 4200

2&3

3I to 57

discharge (not

mercury

recommended

(MBF)

for new

installations)

High intensity

Metal halide

discharge

(quartz)

60 to I20

44 to II5

3000 to 15000

35 to 2000

3000 to 6000

IA to 2

60 to 93

(ceramic)

87 to 95

7I to 82

9000 to 12000

20 to 250

3000 to 4200

IA to 2

80 to 92

The Lit Environment, Osram Lighting, Updated toJune2003.

*Lamp efficacy indicates how well the lamp converts electrical power into light. It is always expressed in Lumens per Watt (Lm/W).

^Circuit efficacy takes into account the power losses of any control gear used to operate the lamps and is also expressed in Lm/W.

'Rated average life is the time to which 50% of the lamps in an installation can be expected to have failed. For discharge and fluorescent lamps, the light output declines with burning hours and is generally more economicto group replace lamps before significant numbers of failures occur.

^Colour temperature is a measure of how 'warm' or 'cold' the light source appears. It is always expressed in Kelvin (K), e.g. warm white 3000 K, cool white 4000 K.

^CIE colour rendering groups: A (excellent); IB (very good); 2(fairly good); 3 (satisfactory); 4 (poor).

**CIE colour rendering index: scale 0 to 100 where: 100 (excellent, e.g. natural daylight); 85 (very good, e.g. triphosphor tubes); 50 (fairly good, e.g. halophosphate tubes); 20 (poor, e.g. high pressure sodium lamps).

In the case of reflector lamps, where the light output is directional, luminous performance is generally expressed as Intensity - the unit of which is the Candela (Cd) (1 Candela is an intensity produced by 1 Lumen emitting through unit solid angle, i.e. Steradian).

The Lit Environment, Osram Lighting, Updated toJune2003.

*Lamp efficacy indicates how well the lamp converts electrical power into light. It is always expressed in Lumens per Watt (Lm/W).

^Circuit efficacy takes into account the power losses of any control gear used to operate the lamps and is also expressed in Lm/W.

'Rated average life is the time to which 50% of the lamps in an installation can be expected to have failed. For discharge and fluorescent lamps, the light output declines with burning hours and is generally more economicto group replace lamps before significant numbers of failures occur.

^Colour temperature is a measure of how 'warm' or 'cold' the light source appears. It is always expressed in Kelvin (K), e.g. warm white 3000 K, cool white 4000 K.

^CIE colour rendering groups: A (excellent); IB (very good); 2(fairly good); 3 (satisfactory); 4 (poor).

**CIE colour rendering index: scale 0 to 100 where: 100 (excellent, e.g. natural daylight); 85 (very good, e.g. triphosphor tubes); 50 (fairly good, e.g. halophosphate tubes); 20 (poor, e.g. high pressure sodium lamps).

In the case of reflector lamps, where the light output is directional, luminous performance is generally expressed as Intensity - the unit of which is the Candela (Cd) (1 Candela is an intensity produced by 1 Lumen emitting through unit solid angle, i.e. Steradian).

One of the problems has been in the 'cheap energy policy' of Government; there may be other good reasons for this, but it has led in the past to a prodigal use of cheap energy, and it is only recently, with a looming energy crisis, that government has woken up to the vital need for savings to be made.

The first line of defence must be in avoidance of waste; for how many times do we pass a building with every light burning in the middle of the day when daylight is quite adequate, or after dark when the building is largely unoccupied. The total amount of energy wasted on a daily basis may not have been calculated, but it is considerable and arguably equals the amount of savings which can be made in other ways.

A particular example of this might be in transport buildings where artificial light is used all day irrespective of the level of daylight. There is no doubt a need for the level of daylight never to drop below the statutory design level, but this can be solved by adopting a system of control which links artificial light to the available daylight to ensure that the design level is maintained, whilst allowing significant reductions in the use of artificial light, which can be off for most of the day.

Was this article helpful?

0 0

Post a comment