1. LED Approach Sequence Flashing System
SFL800D

3. Content
Scope of Application
System Design and Functions
Wiring diagrams
Control Unit
Flashing lights
Customer benefits

4. Scope of Application

5. Scope of Application
The SFL800D serves as approach sequential flashing light system and runway threshold identification flash lights (RTILS) on airports.
The SFL system enables the pilot already to recognize the runway from a long distance and marks the active landing direction.
The threshold identification lights indicate the begin of the runway.
The system supports two different flash frequencies (1 / s or 2 / s).
3 intensity steps allow the adaptation to the actual metrological view.

6. System Design
The sequence flash system is installed complementary to the existing approach center line
The common length is 900 m with a distance of 30 m between the flash lights
The two Threshold Identification Lights (TIL) are placed beside the green threshold lighting.
To avoid short distance glare to the pilot the last 300 m segment in front of the threshold is often not equipped with flash lights. This is especially the case in CAT II & III systems.

7. Differences between Xenon and LED flashing systems

8. Differences in electrical characteristics
Xenon
LED
Sensitivity to moisture
Protections required
Very robust
Work safety
High voltage issues (max. 15,000 V)
Absolutely safe ( max. 70 VDC)
Lifetime
~ 500 to 10,000 hours. High voltage circuitry requires maintenance attention.
> 25,000 hours
Light head dimensions
Small (with separate Individual Control Cabinet)
Requires larger optical output
Inset lights available
Very limited.
Inset light conditions (moisture, condensation, vibration) not beneficial for high voltage Xenon.
Yes, no restrictions.
Max. intensity may be limited by the available optical aperture. Can be solved by twin light combination.

9. Light output from Xenon and LED
Flash intensity shape is close to a rectangular flat light signal ( t ~ 50 ms [milli-secs])
According to the Blondel & Rey calculation, the total light output contributes to the effective intensity
Xenon
Flash is extremely short with a high intensity peak (t < 10 µs [micro seconds])
According to the Blondel & Rey calculation, parts of the rising and falling edges do not contribute to the effective intensity (optical losses)

10. Let’s remember the Broca–Sulzer-Effect
Broca and Sulzer published in ~ that short pulses of definitely visible light of a certain duration will appear brighter than if the pulses lasted longer in time.
It seems that the effect is a result of the visual signal evaluation in the human optic nerve and/or brain (till now no valid explanation available).
The “Broca-Sulzer-Effect” has been confirmed by several scientific studies.
The effect does not increase the physical amount of light but improves the perception!
Broca-Sulzer brightness enhancement occurs at stimulus onset for high intensity incremental targets. Here flash brightness is plotted as a function of duration for flashes of different luminances. Data from Hart (1987) et al.

11. What will be the optimized flash duration?
According the Broca-Sulzer-Effect a flash with a duration of 40 – 70 ms should appear VERY much higher than a longer or shorter flash.

12. Selection of the Flash Duration
The best solution is a 50 ms flash It provides the best perception according the Broca- Sulzer-Effect. The LED current / thermal peak and the thermal dissipation can be handled. The required capacity voltage to provide the flash energy in the 50 ms time can be kept in the SELV range.

13. What is the benefit of overlapping light pulses?
Short distance view The eye resolution can separate all sequenced flashing lights Recognized is the intensity of an individual light e.g. 15,000 cd
Long Distance view The eye resolution cannot separate individual lights Recognized is a virtual light with an intensity formed by all lights covering the smallest viewing angle. (e.g. with 3 adjacent lights = 45,000cd)
Flash Cluster in the Row
Single Flash at the Threshold

14. System Design and Functions

15. The sequence flash system consist of:
Components
The sequence flash system consist of:
Control Unit with the power and communication interface to the field components
Power Distribution Unit to feed the single flash light heads with SELV power and communication
The flash lights (elevated or 12” inset) with the high power LEDs and the control electronics.
Note: the inset lights may be installed by pairs

16. Overvoltage Protection Unit
Principle Cabling
The Control Unit placed in a sub-station supplies the flash system via a single power cable.
The communication between the Control Unit and the flashes is achieved on separate wires of the same power cable.
Inset lights may be installed by pairs to increase the photometric performances
System Layout
Overvoltage Protection Unit
Control Unit

17. Power and communication to the lights
Power Supply to the flashing lights
400 V / 50 Hz or 60 Hz power supply voltage on two wires of the supply cable.
The Power Distribution Unit transforms that voltage down to 36 VAC supply voltage for the flash lights. The safe separation with the extra low voltage level provides a Safety Extra Low Voltage (SELV) with the highest work safety.
Data communication to the flashing lights
Control and monitoring by two other wires of the supply cable.
The control unit sets the required intensity level and the system configuration of the entire system.
Individual address of the flash head defines the time of ignition.
After ignition each flash light sends automatically the actual status to the control unit.
A pair of combined inset lights consists of a master and a slave unit. The function is defined by the internal configuration. Only the master communicates with the control unit.

18. Wiring diagrams

19. Safety Extra Low Voltage
Principle Wiring Diagram and Voltage Levels
400 VAC
HO7RN-F 4-core cable
2 wires for power (400V)
2 wires for control and monitoring
Cable joint
(contractor-made)
Overvoltage Protection Unit
Power Distribution Unit
( = separation transformer)
Safety Extra Low Voltage
(SELV) < 50V
Control Unit
Cable joint
(contractor-made)
Optional connector
(e.g. for electrical frangibility on approach masts)
Connector of the light
E.g. for elevated light with breakable coupling

20. Control Unit

21. Control Unit
Input: 400 V 3 phases
Output: 4-core cable – 2 wires for power (400 VAC), 2 wires for communication
Interface to remote Control and Monitoring System (CMS) via parallel or serial interface.
Local control for the basic functions.
Detailed maintenance and configuration of the system can be done over an external maintenance computer with the optional service software lucDMC.

22. Local Control and Monitoring
Local control for maintenance purposes on the internal control module
5 push buttons to select function (TIL, SFL, flash frequency...) + 1 rotary switch for brightness and remote/local control
9 LED indications show the actual status of the system.
Note: The use of the internal local control should be limited to trained electricians. With opened Control Unit the suitable safety regulations must be applied!

23. Remote Control Interfaces
Parallel (multiwire) interface with in- and outputs on 24 VDC level.
2 redundant CAN-Bus ports
For an optional serial interfacing with any other CMS brand the following interface can be provided on request:
RS-485 (EIA-485) MODBUS/RTU, RCOM, RCOMplus
ETHERNET MODBUS/TCP
PROFIBUS DP

24. Flashing lights

25. Flashing lights – which photometric requirements?
Flashing lights are not specified in ICAO Annex 14 or ADM
However, it seems logical that the beam dimensions should be the same as steady burning lights.
But what about the intensity? Average intensity of 20,000 cd is often excessive and produces glare. FAA limits the intensity to a maximum of 20,000 cd, with a minimum of 8,000 cd for elevated lights and 5,000 cd for inset lights. Many lights of this type installed worldwide.
Ideal solution:
Use the ICAO beam angles
Average intensity for elevated lights: 10,000 cd to avoid glare (meaning peak intensity  15,000 cd as most FAA lights)
Inset lights should be approx. 60% of elevated lights as per FAA, as they are seen at shortest distance.

26. Elevated flash light Flashing lights The elevated type is available as
as a standard light with 12,500 cd * nominal intensity.
or a extra high intensity light with 20,000 cd * for best far distance operation under low vis.
Choosing the standard light helps to increase the LED lifetime.
12” inset flash light
The single inset light provides a nominal intensity of cd *.
To increase the operational effective intensity, two synchronized insets next to each other can be combined to form a single point of light.
* Typical values of the effective Intensity on the highest brightness step.

27. Customer benefits

28. Approach lighting is different!

29. Reduced maintenance thanks to
Customer benefits
Reduced maintenance thanks to
the reliability and long life time of the LEDs (xenon flash tubes have a very short life)
IP68 for all outdoor equipment, including the elevated lights
This is extremely useful for approach lights installed on masts, outside the airport perimeter, above fields, roads or sea...

30. Low power consumption: 20VA per light
Customer benefits
Low power consumption: 20VA per light
Inexpensive and easy installation:
Standard low voltage cable (HO7RN-F), of small diameter; typically:
2,5 mm² from the Control Unit to the first light
then 1,5 mm² to the end of the line
Same 4-core cable used for both the power supply and the communication. No separate bus.
No individual electronic cabinet: only a simple transformer that can be installed in a transformer pit
Safety: SELV at the level of the lights, instead of 400 or 2000V.

31. LED Flashing Lights
First LED Approach Flasher has been operating in Kassel, Germany since April 2013.
Further installations are in
Muenster (Germany)
Nordholz (mil) (Germany)
Frankfurt (Germany)
Geilenkirchen (mil) (Germany)
Finkenwerder (Germany)
Dubai (UAE)
Iasi (Romania)
Innsbruck (Austria)
Warsaw (Poland)
Many more are due to be in operation soon.

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