CUps 1-2013; Javier Díaz-Castro
CUps 1-2013
Rationale for the future change to led technology for outdoor light in La Palma
Javier Díaz-Castro
[email protected]
Oficina Técnica para la Protección de la Calidad del Cielo (OTPC)
IAC
Abstract
The OTPC has studied the available LED technology. As result, the OTPC proposal is to use the LED “PC-Amber”
everywhere in the near future as a substitution of actual HPS and LPS lamps.
REPORT ON THE POSSIBLE CHANGES OF TECHNOLOGY FOR ILLUMINATION THE VILLAGES AT
LA PALMA
The OTPC has been over three years trying to find the right solution to changing the Low Pressure vapour Sodium lamp
(LPS) that we use in La Palma by the new LED technology (Light Emission Diode, also SSL as Solid-State Light). The
reasons are:
1- It will be discontinued soon the LPS lamps and raised its price by becoming rare.
2- LED technology is the immediate future in lighting and growing rapidly and currently (since year 2012) its
energy efficiency competes with LPS lighting devices (energy saving is not longer a parameter to convince
about using LPS).
3- The EU will give grants to change light installations to the current LED lighting and promote this new
technology.
The AMBER LED option:
We consider AMBER LED the best option (first sample installed in Los Llanos 2012) to be used instead LPS. It has
practically no emission below 540nm and above 630nm. Its maximum emission is between 590-600nm, HBW= <17nm
(See figure 1).
FIGURE 1: Spectral response of LPS lamps (white) and AMBER LED (yellow) for comparison.
Weakness of AMBER LED:
AMBER LEDs are less efficient than blue-white light LED but at least uses the same optical and equipment and
therefore physical supports hardware. The present (2013) commercial devices have efficiency between 53 lum/w and 35
lum/w (for outdoor lighting).
The only extra advantage of using AMBER light, besides the protection of dark skies, is the protection of natural
habitats as the amber light is the one that impact the least on living things at night, including humans.
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CUps 1-2013; Javier Díaz-Castro
Besides of the low efficiency, AMBER LEDs are also very dependent on temperature, see figure 2. It means that the
device should have an expensive system to sink the heat from LEDs to get same useful efficiency (normal system has
85ºC on PN junction).
FIGURE 2: Graphic of
efficiency reduction
with the junction (PN)
temperature.
The PC-Amber option:
There is other type of AMBER LED, called PC-Amber, with a wider spectrum with maximum on 595nm and HBW =
80nm. It is a white LED but with an extra phosphor layer that almost remove all the blue emission. It behaves as a High
vapour Pressure Sodium lamp (HPS) but with less emission for wavelengths shorter than 550nm (<4%). We can see
only a small emission on 435-440nm (less than 1/50 the maximum spectral value). (See spectrum on figure 3).
FIGURE 3. Spectrum of the
PC-AMBER LED.
What is been doing elsewhere?:
• In Hawaii, they are using warm white (WW) LED with yellow filters, than behaves as PC-Amber type, In Hawaii’s
case are closer to HPS lamp type with a bigger invasion of the visible spectrum than with PC-Amber. With data from
the maker, it has <14% below 550nm and from a sample we measured 22%. See figure 4.
+ FILTER
=
FIGURE 4. Spectrum of warm white
LED plus a yellow filter (used in
Hawaii Island).
In figure 5 we present a comparison of the spectrum of the three types of lamps: HPS, PC-Amber and WW LED +
Filter.
FIGURE 5. Spectrums
of HPS (yellow), PCAmber (orange) and
WW LED + Filter
(green).
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CUps 1-2013; Javier Díaz-Castro
• In north of Chile, the new “Norma Luminica” allows the use of warm white LED with less than 15% of radiance for
wavelength shorter than 500nm. Actually, it means white LED with colour temperature less than 3.200ºK. Figure 7
shows a typical warm white LED of 3.000ºK with less than 15% of radiance below 500nm.
FIGURE 7 Spectrum of a
typical warm white LED
of 3.000ºK with less than
15% of radiance below
500nm (the one allowed
for Chile).
Specifications of Commission 50:
The new specification of Commission 50 of IAU (2012) is limiting spectral radiance emissions for wavelength shorter
than 500nm.
What is OTPC framework?:
The OTPC already applies less than 15% for wavelength shorter than 500nm for all white LEDs use before
midnight on pedestrian areas. After midnight all lights should be LPS type (in La Palma).
For HPS type equivalence on LED we have chosen 550nm as reference. So, radiance of LED to use as HPS
lamp should be less than 15% below 550nm (measured between 350-800nm). We use HPS in Tenerife Island
and in urban areas of La Palma before midnight. By now, the HPS lamps will be in the market for many
years.
Table 1 shows data of relative emission for wavelength shorter than 550nm and 500nm for different types of
lamps:
LÁMPARA
VSAP/HPS
PC-Amber
3000ºK+Filter
3K/4K+FILTER
Amber
LED 3000ºk
LED 5000ºK
LED <3200ºK
< 440nm
2%
0,30%
0,08
0,07%
-4%
4,40%
< 500nm
7,50%
0,70%
0,42
0,90%
-12%
27%
15%
< 550nm
10,60%
4%
13,9
22%
-25%
47%
Lum/w
(react)
100
75
--60
88
Lum/w
device
80
63
63
-52
83/70
Observaciones
Fabricante
Muestra
HBW = 13 nm
TABLE 1. Technical parameters of percentages of radiance emission and efficiency data (Lum/w) for
wavelength shorter than 550nm and 500nm
WHAT CAN WE DO?
The situation (summary):
1.
2.
3.
4.
5.
Low Pressure Sodium (LPS) is used seldom (only Norway, rural zone in England, Tucson, La Palma, ...) but
right now is not used anymore in new installations (but La Palma).
LEDs (white) are becoming more efficiency than LPS and HPS system. As a consequence LPS increases its
prices and will be disappear from market.
The AMBER LED (monochromatic) uses other technology than white LED and has no new progress on
efficiency. It is established (2012) in no more than 50 lum/w (complete light fixture) and normally light makers
do not get more than 30 lum/w (not good heat sink).
AMBER LED efficiency decrease with the temperature junction (PN) and it is difficulty and very expensive
heat sink system to maintain it low (see graphic on figure 2 considering normal temperature junction to be 7585ºC).
In the best case studied up to 2012 the AMBER LED is 20% less efficiency than PC-Amber (in 2013 the PCAmber has increased 10% the efficiency respect 2012).
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CUps 1-2013; Javier Díaz-Castro
6.
As far as we know, the only place in the world using AMBER LED for outdoor lighting is La Palma (Hawaii is
using white LED with filter, a little worse than PC-Amber because uses more spectral bandwidth).
7. The low efficiency of AMBER LED does not meet the new Spanish regulation of energy efficiency
(>65lum/w).
8. AMBER LEDs are less efficiency than previous LPS installation and the cost is 4 times higher.
9. AMBER LED cost is actually about 50% more than PC-Amber due to its rare use and the especial heat sink
used.
10. PC-Amber and White-LED are getting cheaper with time.
11. Using AMBER LED the number of inquiries and complains from the local administration is expected
significantly increase in the future.
Advantages of PC-Amber:
1.
2.
3.
4.
5.
6.
7.
8.
PC-Amber (year 2012) is about 65-50 lumen/w. Although it is lees efficiency than white LED (20%) PCAmber uses the same technology white LED. Moreover, the PC-Amber has an extra phosphor layer (it reduces
the blue radiation) and over take advantage of white LED technology with no extra assembles cost.
PC-Amber has a continuous spectral emission (contrary to HPS, see figure 5) and its colour rendering (cri=40)
is better than HPS (cri=20). Its efficiency is similar to HPS (better optic light distribution).
PC-Amber has no problem with the heat dissipation and uses the advanced of white LED technology.
The replacement with AMBER LED could be up to 4 times more expensive than to do it with present LPS
lamp; with no energy saving and no advantages to citizens. The replacement with PC-Amber will increase
(year 2012) by 2 with 20%-40% energy saving and increase on colour rendering to a 40%.
On other hand, the wider spectrum of PC-Amber gives to citizens a better feeling of light level (respect to
monochromatic amber) due to the eye shift sensitivity to blue-green at night. It means PC-Amber would allow
reduce the light level by 20-30% with same safety conditions for citizens.
PC-Amber is used now in Tenerife Island and light protected areas in mainland.
We are also in connexion with maker of the LED solution for Hawaii to find a filter that meets our
specifications as PC-Amber does.
Other good advantage of using LED with good optic light distribution is that the light from LED luminaries,
send outside the street, is reduced by a factor of 2. The reflexion of surrounding areas, outside street, are over
30% (soil, facades, etc) and the street is at least 1/3 (dark asphalt is 7% in La Palma). It will mean that the
actual reflected light will be reduced by a factor of 1.8 (good utilance factor). It will reduce the reflected light
and mitigate the increase of spectral lines in the sky background.
DRAWBACKS TO BE CONSIDER:
1) The PC-Amber contaminates important spectral region (H-alpha - 6562.8 and [OIII] 5006.8 red shifted).
2) Chile and Hawaii have observatories, higher and away from sources of contamination than ORM, so we should be
more conservative than them.
However, if all the lights on La Palma would be replaced by PC-Amber, it will probably increase the sky brightness
between 560 and 640 nm by ~ 0.05 mag, which isn't too bad. Considering the reduction on reflected light, we (OTPC)
expects this to be smaller.
ACKNOWLEDGEMENTS
The OTPC acknowledges comments by Casiana Muñoz-Tuñón (IAC) , Chris Benn (ING) and Sergio Ortolani (Univ.
Padua).
NEW COMMENTS:
Any comments will be appreciated. Please, send it to [email protected] (Javier Díaz-Castro)
The Canarian Observatories Updates are published by the Instituto de Astrofísica de Canarias (IAC), c/Via
Láctea s/n, 38205 La Laguna, Tenerife, Spain. The IAC is an internationalized Spanish research center that
manages the Canarian Observatories that currently home to telescopes and other instruments belonging to 60
scientific institutions from 17 different countries.
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