# How is the ALSF-II approach lighting system built and powered?

The ALSF-II approach lighting system includes lead-in groups, a decision bar, red side bars and sequenced strobes:

ALSF-II approach lights for KRFD - Chicago-Rockford Intl (source).

Does anyone know the number and type of lights used, how they are arranged (distance and slope) and how much power is required to feed the full system?

The specifications for an ALSF-2 (and other approach lighting systems) can be found in FAA JO 6850.2B - Conveniently titled "Visual Guidance Lighting Systems."
As an FAA order these are obviously US-specific, but other jurisdictions' guidance is probably similar.

The ALSF-2 is a High Intensity lighting system, so lights used in the system are defined in the FAA order as follows:

## High Intensity Systems.

1. Specification FAA-E-2408b, 300-watt, 20A, PAR-56 lamps for steady-burning, aboveground, white lights with Specification FAA-E-982 lampholder.
2. Specification FAA-E-2408b, 500-watt, 20A, PAR-56 lamps for steady-burning, aboveground, colored lights with Specification FAA-E-982 lampholder.
3. Specifications FAA-E-2952 or FAA-E-2491 approach lights, 500-watt, for all semiflush lights.
4. Specifications FAA-E-2628b or FAA-E-2689a for all sequenced flashers.

From the number of required lights we can then derive the total system power used for an FAA-Specified ALSF-2 lighting system -- As I'm not fond of doing math it's fortunate that some manufacturers have already done this for us, and a full system (with all the flashers) requires approximately 104kW (varying slightly depending on input voltage). Actual utility power consumption will vary based on the efficiency of certain components but will likely shake out to something around 104kVA since the incandescent lamps have a power factor close to 1.0.

• @mins You are correct - I misread the sheet, and that's apparently the power for the flashers only (which makes a lot more sense if they're using incandescent lamps). Adding your number to that number and assuming a power factor of 1 gives a little over 100kVA for the whole system, which does seem much more reasonable with incandescent lights! Jul 13, 2016 at 17:07
• I thought about this figure being the flashers power only too, but was confused by the non-linearity when the number of flashers increases (page C-8). But now my second thought is it could be because energy is stored in a capacity (BTW a flash tube can deliver 100 μs pulses, not an incandescent filament), discharged at interval and they improve time efficiency (duty cycle) in parallel with power supplied.
– mins
Jul 13, 2016 at 19:28
• @mins Yeah, the flashers have an efficiency less than 1.0 because of the reactance in the circuit (we have to rectify to DC and charge capacitors, or step up the AC in a coil to spark the strobe). Considerable power savings could be had by converting the whole mess to LEDs, but as far as I know that's not formalized in a standard/technical order yet Jul 13, 2016 at 20:51