Download Output comparison: 50 mm LED, quartz halogen

LIGHTING DESIGN
& APPLICATION
South African middle and high income homes use
50 mm diameter reflector lamps for general lighting,
but these weren't designed for this purpose.
Output comparison: 50 mm LED,
quartz halogen reflector
In bedrooms, these lights are typically
placed one in each corner with a fifth
light sometimes added in the centre,
totalling between four and five lights
and light points. The rest of the house
would have four lights in the study; four
to eight in bathrooms and kitchens; six
to twelve in dining rooms, television
rooms and lounges; one light per metre
in passages, and between four and six
lights in the entrance hall. Hotel rooms
commonly feature up to 15 light points.
The standard power of these lamps
is 50 W for both the 12 and 230 V
versions. The lighting power density
in these homes should be below
5 W/m 2 but 50 lamps with a total
load of 2500 W in a 200 m2 house
would have a light power density of
12,5 W/m2, which is not compliant
with SANS 204. A 15 m2 bedroom with
four 50 W lamps would have a power
density of 13 W/m2. We cannot afford
this energy waste in South Africa.
by André Blignaut and Robert Henderson, Eskom
Fig. 1: Goniometer type (a) and type (b).
The authors conducted comparative
light output testing of 50 mm LED
and quartz halogen using intensity
distribution measurements, the zonal
flux method, the integrating sphere and
electrical measurements.
Testing methods for light output
Intensity distribution measurements
Light intensity distribution curves provide
designers with information on how
light is distributed from all angular
positions. A goniometer measures the
light intensity from all the angles and a
Fig. 2: Goniometer with moving mirror.
September 2013 - Vector - Page 25
curve is plotted. For symmetrical lamps
and luminaires, the number of points
measured can be decreased by means
of symmetry. The total light flux can then
be calculated by means of the zonal
flux method.
The goniometer usually keeps the
luminaire or lamp in a fixed
position to avoid changes in lamp
temperature, as shown in Fig. 1 (a).
Alternative goniometers which rotate
the lamp or luminaire, shown in
Fig. 1 (b), can be used and the results
corrected for the change in lamp
temperature.
The zonal flux method
The zonal flux method uses the measured
light intensity at a point in the imaginary
sphere and then assumes that its value
is the same around the sphere within a
preselected band. The product of the
intensity and the area of the band will
give the light flux within that band. This
is repeated for each band and typical
zonal factors for 1, 2, 5 and 10° can
be found in Table 1.
Zonal factors for 2°, 5° and 10° zones
2° zones
5° zone
10° zone
Zone limits
(degrees)
Zonal
factors
Zone limits
(degrees)
Zone limits
(degrees)
Zonal
factors
Zone limits
(degrees)
Zone limits
(degrees)
Zonal
factors
0–2
0,0038
0–5
175 – 180
0,0239
0 – 10
170 – 180
0,095
2–4
0,0115
5 – 10
170 – 175
0,0715
10 – 20
160 – 170
0,283
4–6
0,0191
10 – 15
165 – 170
0,1186
20 – 30
150 – 160
0,463
6–8
0,0267
15 – 20
160 – 165
0,1649
30 – 40
140 – 150
0,628
8 – 10
0,0343
20 – 25
155 – 160
0,2097
40 – 50
130 – 140
0,774
10 – 12
0,0418
25 – 30
150 – 155
0,2531
50 – 60
120 – 130
0,897
12 – 14
0,0493
30 – 35
145 – 150
0,2946
60 – 70
110 – 120
0,993
14 – 16
0,0568
35-40
140 – 145
0,3337
70 – 80
100 – 110
1,058
16 – 18
0,0641
40 – 45
135 – 140
0,3703
80 – 90
90 – 100
1,091
18 – 20
0,0714
45 – 50
130 – 135
0,4041
50 – 55
125 – 130
0,4349
55 – 60
120 – 125
0,4623
60 – 65
115 – 120
0,4862
65 – 70
110 – 115
0,5064
70 – 75
105 – 110
0,5228
75 – 80
100 – 105
0,5351
80 – 85
99 – 100
0,5434
85 – 90
90 – 95
0,5476
Table 1: Zonal factors.
The authors used 2,5° intervals for
testing the downlighters. The lamp
flux is the product's light intensity
and the sum of the solid angles
(see Fig. 2) given in the formula in Fig. 3.
This method required that the lamps
be rotated by hand and the intensity
recorded manually at each point. This is
time consuming and the new automated
system will yield results faster.
The integrating sphere
The integrating sphere is a
comparative method to determine
the light flux of a lamp or luminaire
(see Fig. 7) The system uses a reference
lamp of known light output to be placed
in the integrating sphere. A reading is
taken and the reference lamp replaced
by the test lamp. A second reading is
then taken.
Fig. 3: Zonal factor angles and factors formula.
Two correction factors must be taken
into account: the effect of the physical
interference of the reference lamp and
the test lamp.
When testing these small downlighter
lamps, the interference was not
measureable and considered to be
unity. The position of the baffle screen
and the direction of the lamps were kept
constant for all tests.
The total light output was initially
measured, but was revised to
Fig. 4: Light distribution of a halogen downlighter.
September 2013 - Vector - Page 26
measure only the downward light
for the lamps used in the residential
sector. The main reason for this was
that the upward light was not used
in the general lighting applications
when the lamps are installed in
the ceiling.
The results of measuring the downward
light only are lower than the published
information from the suppliers. In some
instances, the difference was large and
this will be reflected in the results. The
revised system is the 2π system and not
the normal 4π system associated with
the integrating sphere (see Fig. 6).
Fig. 5: Light into the ceiling space from a quartz halogen and a LED (lamp).
Electrical measurements
The lamps were connected to a
controlled voltage supply of 230 and
12 V respectively, as required by the
lamps.
The power, apparent power and power
factor were measured using a Fluke
43B power analyser and referenced to
a Yokogawa power analyser (see Fig. 8).
Results and discussion
Using the 2π system, a sample of
quartz halogen lamps and LEDs was
tested (see Table 2). Fig. 9 shows the
light distribution from the 230 and
12 V downlighters.
The quartz halogen lamps have lower
light flux and efficacies than expected
at 230 V, while the 12 V quartz halogen
lamps have higher efficacies because
transformer losses are not included.
The LED lamps operating at 230 and
12 V have lower light output compared
to the quartz halogen lamps. The lamps
were selected for similar beam angles,
however the LED lamps have a faster
drop-off after 50% of the peak.
The quartz halogen lamps have a
higher upward light component than
the LED lamps, as was expected
(see Figs. 4 and 5).
Conclusion and remarks
The LEDs can replace the quartz halogen
lamps. However, the LEDs’ power must
be selected to provide the same light
output. This depends on the supplier
and the model used.
End-users must be informed what the
terms “lumens” and “beam angle”
mean so that they can purchase the
correct lamp for their application. This
will achieve greater acceptance of LED
by the middle and high-income sectors,
and the reduction in energy use the
Fig. 6: The 2π proposed system.
Lamp
Lamp description
Voltage
Efficacy
lm/W
Light
lm
Power
Watts
Power
factor
VA
Var
Quarts halogen lamps
RQ7
50 W Gu10 quartz halogen
230
6,58
324
49,2
1,00
49,70
3,00
RQ9
50 W Gu10 quartz halogen
230
7,26
333
45,8
1,00
45,90
3,40
RQ10
50 W Gu10 quartz halogen
230
8,07
381
47,2
1,00
47,30
3,60
RQ14
50 W Gu5,3 quartz halogen
12
18,50
838
45,3
1,00
45,30
1,20
RQ17
50 W Gu5,3 quartz halogen
12
17,43
800
45,9
1,00
45,90
1,00
RQ20
50 W Gu5,3 quartz halogen
12
15,35
698
45,5
1,00
45,60
1,20
LED sample lamps
P10
6 W LED GU10
230
49,97
310
6,2
0,65
9,6
7,3
V44
6,5 W PAR16 LED GU10
230
44,13
269
6,1
0,89
6,8
3,1
R55
6,5 W LED GU10
230
51,77
337
6,5
0,43
15
13,6
R70
6,5 W LED GU5,3
12
52,16
339
6,5
0,61
10,6
8,4
P20
6,5 W LED GU5,3
12
62,10
397
6,4
0,97
6,6
1,7
V49
6,5 W MR16 LED GU5,3
12
46,70
290
6,2
0,63
9,7
7,5
Table 2: Electrical and illumination results.
September 2013 - Vector - Page 28
Fig. 7: The modified comparative integrating system.
Fig. 8: Circuit for testing 230 V lamps.
colour rendering index (CRI) etc. to help
them make a more informed selection.
Light output is most important to users
when switching to LED or CFL: they
require from these lamps the same
light levels and colours which they
are accustomed to. Light output is
linked to colour appearance and
colour rendering. Incandescent lamps,
including quartz halogen lamps, provide
a "warm" appearance and a continuous
spectrum, so their colour rendering is
100. CFLs and LEDs are made with
different CRIs, ranging from 60 to 90
and colour temperatures from 2700°K
to 6500°K.
Acknowledgment
This article is based on a paper
presented at the ninth IESSA
Conference in 2013 and is published
here with permission.
References
[1] J Pan, F Minand Y Li, Everfine Photo-e-info,
Hangzhou, China, and F Qian, Hangzhou
Institute of Calibration and Technical
Supervision, Hangzhou, China,“Total
luminous flux and chromacity measurement
for led luminaires using the absolute
interating sphere method”, CIE 2011.
[2] B Rowell, Lighting design and application, a
practical guide for lighting practionioners.
Fig. 9: Light distributions from 230 and 12 V downlighters.
offer will help lower the nation evening
peak load.
Most buyers in the domestic market use
electrical power as the deciding factor
when selecting lamps while others
consider price and brand. Users need
more technical information on light
flux, lumen output, colour temperature,
September 2013 - Vector - Page 30
[3] AR Bean and R H Simons,Lighting Fitting
Performance and Design.
[4] R H Simons and A R Bean, “Lighting
engineering applied calculations”.
Contact André Blignaut,
Eskom, Tel 011 629-5111,
[email protected]