Dimming cabin lights

[Mr Incognito]

I wasn't sure whether this was the correct forum for my query but here goes! Why are cabin lights dimmed for both take off and landing? During an HP&L lecture yesterday the point was raised by a fellow student but no one knew the answer!

Cheers.

[Guy Devane]

Dimming the lights requires less power from the generators, which of course are engine driven, and this allows lots of extra power for take-off or the go-round on landing. Some aircraft (e.g. BAC1-11) could not get airborne at night with the lights on.

[Zeitgebers]

Only happens at nite. It is so your eyes are adjusted to low light conditions should an evacuation be necessary, so you can fully enjoy the ride down the slide.

[GotTheTshirt]

Well now you know how to crash a BAC1-11 !!

The dimming is to allow your eyes to adjust to low light conditions which is just what you would have in a crash situation. Those emergency lights are not exactly blinding !

[Captain Airclues]

Could somebody please show Guy Devanes answer to Figment.

Airclues

[VH_KAM]

In my company cabin lighting is turned on full bright during all takeoffs and landings, whether at night or day...

I guess the logic for this is the cabin crew will have a good view of what is happening inside the cabin, and it assists in improving the visibility of the aircraft to others in the sky.

[jonno]

Hey Guy Devane,
I really hope that your response to this question on dimming lights was a joke, otherwise you've just lost all credibility as far as common sense is concerned, what a
stupid answer!

[Guy Devane]

Jonno
Well done- I was joking of course, I am amazed that you even thought for a moment that I could be serious. I thought a little light heartedness on this forum, where everyone takes themselves so seriously, would not go amiss. I think at least Captain Airclues appreciated my "stupid" answer and thought it might make the basis of a cartoon by figment.
I am sorry it did not amuse you.
signed:
Guy Devane ( from guide vane - as in jet engine? joke?)

[Lee Dingedge]

Guy,

Don't worry - me and my mates liked it. If you look closer you will see that jonno is Australian, which will explain everything. He probably doesn't even know what a BAC 1-11 is!
Lee Dingedge (as in leading edge, for jonno)

[Hew Jampton]

Having done a stint on the BAC111, I'm not sure that there wasn't an element of truth in the original joke! Bloody good aeroplane but talk about converting Jet-A1 directly into decibels.

Hew Jampton (Cockney rhyming slang - Hampton Wick - geddit?)

[boofhead]

One reason the Russian fighter pilot could not identify the Korean 747 in 1983 was that the crew had all their external lights off, thinking that would reduce the electrical load enough to make a difference to fuel burn. A common practice in that airline at the time.
SQ turns off the logo light above 10,000 for a similar reason, and does not use the landing lights below 10,000 if the strobes are working.
All these examples are to show that what is ridiculous to us makes a lot of sense to some airline managements.
But I thought the BAC111 joke was a good one, having watched a takeoff at a small island airport by a crew who ran out of water meth half way down the strip (or forgot to turn it on?). Made a big dust cloud in the overrun area!

Boofhead (A derogatory term)(used in Australia)

[This message has been edited by boofhead (edited 13 February 2001).]

[This message has been edited by boofhead (edited 13 February 2001).]

[Captain Airclues]

boofhead

The logo lights are turned off above 10,000ft to extend the life of the bulbs, not to save electricity.

Airclues

[Hew Jampton]

A major UK airline did a trial many years ago and concluded that it was repeated switching on and off that reduced lamp life. A year or so ago, I noted that a major Australasian airline keeps its landing lights on all the time, even on the ramp, at a very low power, presumably for the same reason.

Anyway, what's cheaper, a few lamps or the lives of all on board? KAL007 wasn't the first and won't be the last.

[Hudson]

In an emergency evacuation, the dimming of cabin lights is a complete waste of time. It is known that one bright light will completely ruin night vision and that 30 minutes is needed for full night adaption. And night adaption is the only reason why traditionally cabin lights are dimmed.

The cabin crew have their night vision already shot to pieces even before the take off starts as they mill around the galley area (plenty of bright lights there) and as they walk down the aisle checking seat belts. That is because many pax leave reading lights on which which are in full view of the cabin crew.

The cockpit crew will have never gained night vision adaption as they taxi due to myriad of airport lights, runway lights and the beams of their own landing lights, let alone the overhead map-reading lights.

At least one major airline to my knowledge realises that dimming of cabin lights is all a big myth and leaves them on for take off and landing. One spin off is that pax wearing glasses can better see exactly where the position of the emergency exits are. It is well known that people who need glasses to see adequately, are invariably handicapped if the ambient light is poor as in a darkened or dimly lit cabin. Pax that take the trouble to read the emergency procedues card located in the seat pocket will often turn on their overhead reading light when the cabin lights are dimmed. Scratch their night adaption. Dimming the lights is significantly counter-productive to the elderly and those who wear spectacles.

Some third world cabin crew even turn off all the cabin lighting in full daylight for take off and landing - then turn it back on in flight! That is because their ops manual says that cabin lights must be turned off for ALL take off and landings. That is a myopic viewpoint for sure.

A similar mentality once existed at Manila airport where all the VASIS lights for runway 24 were showing crazy angles. To a pilot report of contradictory VASIS indications, ATC replied that this was probably the result of a minor earthquake causing damage to the VASIS boxes. But because their ATC Manual stated that the VASIS must be left on for all arrivals, they did just that..

Far better for airlines to leave the cabin lights on full bright for take off and landing, so that pax can note the position of the emergency exits in front and back of them. Anyway, if the aircraft catches fire, the glare of the flames are really going to ruin your day -and your night vision.

[boofhead]

Capt A: I personally believe logo lights enhance an airplane's visibility at night and make it easier to see and avoid. Very cheap insurance, but if your airline thinks the bulbs are more important than the safety of the airplane and all aboard, that merely proves my point.

[Hew Jampton]

Hudson
With all due respect (as they say) what a lot of tosh!

"The cockpit crew will have never gained night vision adaption as they taxi due to myriad of airport lights, runway lights and the beams of their own landing lights, let alone the overhead map-reading lights." None of these lights (how can they see their own landing lights, anyway?) will be bright enough to make much difference to their night adaptation.

Cabin staff have emergency torches, so night vision adaptation is not so much of a problem for them. I note that at least one European airline's cabin crew hold their torches in their hands for takeoff and landing, and they wear their gloves (fire). Sounds eminently sensible to me, and a pity that other operators don't require the same.

"that people who need glasses to see adequately, are invariably handicapped if the ambient light is poor " Rubbish!


[This message has been edited by Hew Jampton (edited 18 February 2001).]

[jonno]

Thanks Boofhead, I agree!

[Paulf]

Guys,
I was told when studying for my AMEL that the reason for dimming lights on approch to airfields in built up area was a UK requirement from the early days of aviation to avoid scaring people on the ground who would not know what the lights in the sky were.Even if this is not true - it sounds good
(when in doubt ask an engineer for an answer!!)

[bunyip]

And its funny that the guys who turn out all their lights enroute are the same ones who taxi around on the ground with landing lights, turnoffs and wing lights all on, never mind the glare and nuisance to others. Especially the FOs who slap on the strobes and lights when cleared to line up and "gotcha" the poor slob just landing.

[QAVION]

"A year or so ago, I noted that a major Australasian airline keeps its landing lights on all the time, even on the ramp, at a very low power, presumably for the same reason."

This is not a procedure, but, I hear, a quirk of the electrical system on the 747, Hew. Normally, in flight, there is a low voltage constantly applied to the landing lights to keep the lamps warm, with the landing lights in the OFF position. However, in certain configurations of power on the ground, the lamps also illuminate(using this same low voltage source). Unfortunately, I don't have any detailed wiring diagrams with me at the moment, so I can't tell you exactly what triggers the on-ground lamp illumination. It has something to do with either the Ground Service or Ground Handling Busses (when no power is on the Main AC Busses).

Rgds.
Q.

[boofhead]

For Quavion. I have flown the 747-200, 300 and 400 and am not aware of any such problem with the landing lights; they can be switched off on the ground or inflight. When in flight and clean, they operate on reduced voltage.
Some carriers choose not to have a taxi light and use the landing lights on the ground instead.
Another example of strange thinking!

[basil fawlty]

Mr incognito, the answer is very, very simple. The cabin lights are dimmed at night for T.O and landing merely so that the pax can see out of the windows! (less reflection!) Seems that testicles outnumber brain cells on your course!

[QAVION]

"Very cheap insurance, but if your airline thinks the bulbs are more important than the
safety of the airplane and all aboard, that merely proves my point."

Agreed, but it might not be quite as cheap as you think ;)

Sure, bulbs are relatively cheap, but if you start adding labour costs, cherry picker hire/purchase costs (if we're talking 747's), delay costs (if headed to a place where logo lights are compulsory),...

Some aircraft now have 3 lamps per side (probably not for visibility, but for redundancy).

Rgds.
Q.

[QAVION]

"I have flown the 747-200, 300 and 400 and am not aware of any such problem with the landing lights;"

So this means it doesn't exist, Boofhead?

The latest info I have is that the PSEU (Air/Ground computer), on power down, has the possibility of latching in either Air or Ground mode. Latched in Air mode, the PSEU will put the lights on dimly when the aircraft is powered by the Ground Service Bus.

Being a pilot, I doubt very much that you've seen a -400 powered by the GSB ... and would probably complain if it was.

Q.

[shopsywhopsy]

PA on NZ 737 "because we flying to Invercargill we will dim the lights"

[boofhead]

Sorry Quavion, I don't follow your points.
Maintenance is usually done under contract, so cherry pickers and such will not cause extra cost. If the bulb is out the MEL can be used to get to Base where the lights can be fixed by your own blokes who are paid whether they are fixing the airplane or not.
The landing lights on ground power are not really relevant, are they?

[Centaurus]

So what's the real reason for dimming the cabin lights or has it been well and truly lost in the myths of time. Is it for a lovely view of the towns at night or secretly because few passengers eat carrots for night vision nowadays - preferring fast food.

[Dr Feelgood]

My brother-in-law asked the original topic question and the combined 50 years of experience in the family was unable to give a positive reply.
What we have figured out is this.
1. Night adaption.
2. Subconscious learning. These were the last lights on and they mark the exits.
3. Improved view out for interested passengers.
4. The warm, dark environment is relaxing, thus having a soothing effect on nervous pax.
5. It says so in th e book!
Anymore guesses?

[QAVION]

"Maintenance is usually done under contract, so cherry pickers and such will not cause extra cost."

[To Boofhead] Unfortunately, there are certain things under many aviation maintenance contracts which don't incur extra costs and there are certain things which do. Our airline charges customers extra for things like cherrypickers. An engineer with a screwdriver comes a lot cheaper than an engineer with a cherrypicker :-) And on the subject of contracts.... A daredevil handyman with a stepladder would obviously be cheaper to contract than an engineer with a cherrypicker... but, thankfully, there are laws in many countries to prevent this.

"If the bulb is out the MEL can be used to get to Base where the lights can be fixed by your own blokes who are paid whether they are fixing the airplane or not."

But what happens when an MEL specifies that an item be fixed/fitted before the aircraft departs to a country? I must admit, I hadn't read our Logo Light MEL for a while and had forgotten the details (so I re-read them):

It specifies that if the lamps are inoperative, the aircraft can depart provided TCAS is OK. However, when going to the USA, operations are restricted to one night arrival and one night departure only. Sounds OK, too, but on some days our aircraft have to make three stops in the USA before they return home.

"The landing lights on ground power are not really relevant, are they?"

Previously, I was simply commenting on what someone (else) perceived as a "feature" (rather than a design bug). You _seemed_ to suggest that I didn't know what I was talking about simply because you had never come across this anomaly before (in your many years of experience)(???). I apologise if this was not the case.

Rgds.
Q.

[Royan]

Cabin Lighting: -
Must be dimmed before every take-off and landing
Must never be in total darkness during flight.
http://www.newscientist.com/lastword/answers/lwa353machines.html

[boofhead]

For Q..looked at the MEL last night and the company I work for uses FAA version. Logo lights are not required so they can be out with no restrictions, and will usually be fixed on rtb. For what that is worth.

[maxmobil]

During emergency training we were told that the main reason for dimming of cabin lights is to enhance recognition of an exterior fire, should any rejected T/O or emergency during landing occur.

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This Airbus is o.k., but why did it come with a RENAULT key ??

[ITCZ]

You guys are getting your knickers in a twist without actually pointing to a definitive study or case.

Most of the ideas put forward here are simply the ideas that you heard way back when and never questioned. Reminds me of the thread on the space shuttle booster diameter being determined by the designers of Roman roads.

Anybody got a REASONED reason for dimming/not dimming the lights?