Pflueeb From United States of America, joined Jun 2005, 14 posts, RR: 0 Posted (10 years 11 months 1 week 4 days 20 hours ago) and read 9079 times:
Hello! I've been lurking on this excellent website for years now and FINALLY joined after what I saw last night.
Here in Las Vegas I saw a Southwest (WN right?) 737 coming in to land and its under-the-wing landing lights as well as the 2 lights on the nosegear were wig-wagging back and forth. Alternating slowly in a harmonized fashion.
I've never seen this in all of my years of plane watching. You see this effect on locomotives but not airplanes. Their landing lights are always in a steady burn.
What does this mean? Anybody know? Thank you and I look forward to being a member here!
PHLBOS From United States of America, joined Mar 2004, 7634 posts, RR: 21
Reply 1, posted (10 years 11 months 1 week 4 days 19 hours ago) and read 9049 times:
I believe only WN's 733s and maybe 735s are equipped with this strobe-light feature; it's was either on Boeing's option list or WN added it (aftermarket?) for a special effect. Their 73Gs (that I've seen land at PHL) are the standard steady burn.
Welcome aboard, BTW.
"TransEastern! You'll feel like you've never left the ground because we treat you like dirt!" SNL Parady ad circa 1981
FLY2HMO From , joined Dec 1969, posts, RR:
Reply 15, posted (10 years 11 months 1 week 4 days 7 hours ago) and read 8581 times:
Most of the answers posted so far aren't accurate.
The purpose of the alternating light is to make the plane more obvious to other traffic during day (and night). It is easier to pick up flashing lights using your peripheral vision than to pick up steady lights during the day. Also, the lights burn steadily at a predetermined altitude AGL (from what I've seen, just before overflying the runway threshold, 200ft?). Aircraft with these installed usually have an option for either steady burn or pulse. These lights have been available for GA planes for quite some time.
Same reason for blinking "Ditch lights" on a train. They're to be visible to the motorist at the crossings, since the train will most always be in the peripheral vision of a vehicle (or pedestrian) crossing a rail crossing. At night time though I would think the pilot wants his landing lights on solid for the visibility even before just getting to 200ft AGL. In terms of a landing plane, 200 AGL isn't much.
StealthZ From Australia, joined Feb 2005, 5896 posts, RR: 38
Reply 18, posted (10 years 11 months 1 week 4 days 6 hours ago) and read 8524 times:
Quote: I was under the impression it is a conservation method. Alternating the lights extend their lives compared to burning them steady.
Quote: Quoting GQfluffy (Reply 7):
Huh. I thought turning lights (fluorescent, halogen, zeon, incandescent) on and off were harder on the bulbs then just leaving them on...
I believe that's true for all bulb types except incandescents.
Not so either... It is especcially true of incandescents, the constant flashing causes the filament to vibrate(constant expansion/contraction).
Pulsing the lamp does not extend it's life over a steady state, it minimises the reduction in life that would be caused by flashing it on and off.
The rise & fall in intensity is also more eyecatching than on/off, that is why the rotating beacons on emergency vehicles etc were more noticable than simple flashing lights
Visibility is greatly enhanced, from personal experience at SYD watching hundreds of QF Dash-8 approaches, those with pulselite systems stand out from the haze much earlier.
Birds eyes have a much higher "flicker rate" than humans, hence the spirals and patterns on Prop spinners and fan hubs so I would think that benefit is a minimal but welcome bonus.
If your camera sends text messages, that could explain why your photos are rubbish!