ATLflyer From United States of America, joined Jan 2006, 802 posts, RR: 0 Posted (9 years 8 months 2 weeks 5 days 18 hours ago) and read 2598 times:
I flew to Miami last Thursday and back to Atlanta this morning on Air Tran, and I noticed that on both planes the light covers had turned a dark, unattractive yellow color. Parts of thel light cover looked ok, but the majority was a yellowish color. Does anyone know why lights on airplanes turn this particular color? Also, it seems to me that I only notice this on Boeing planes; Airbus seems to always have clean, white light.
Quoting EMBQA (Reply 1): For the same reason overhead florescent lights do the samething. The light effects the plastic and causes it to brittle and turn yellow.
More percisely, IIRC, it's the UV output of the lights which causes the plastic to change color as well as become more brittle. It also causes colored paper to fade (witness any display in a school/office building).
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Warreng24 From United States of America, joined Nov 2005, 721 posts, RR: 0
Reply 6, posted (9 years 8 months 2 weeks 5 days 16 hours ago) and read 2437 times:
It is correct.
Most aircraft use florescent lighting. Florsecent lighting is very common, cheap, and is very energy efficient (compared to incandescent lights).
However, florescent lighting provides a very large spectrum of light waves. Most are towards the upper end of the visible spectrum.
The florescent lights have a layer of phorphorus on the inside of the blub. This phorphorus flilters out all the wavelenghts that are above the visible light waves. This is mostly ultra-violet light. Sometimes as the bulb's age, the phorphporus ages as well, and allows a greater amount of ultra-violet light through.
Ultra-violet light adversely affects plastics. It clouds them, yellows them, and makes them brittle. Look at most car head lamps. The lenses are sometimes made of plastic. As the car ages (and is affected by ultra-violet light from the sun) the plastic will turn yellow or get cloudly. This is especially true of "clear" plastics.
The plastic resin used by Boeing's suppiler must be more supectiable to yellowing than the plastic resin used by the Airbus supplier.
On the other hand it may just by the bulbs. Warm White florescent bulbs produce a "warmer" more reddish-yellow light. Cool White florescent bulbs produce a "cool" more pure "white" light. AirTran (as the OP mentioned) might prefer using the Warm White bulbs.
As we move to LED based lighting, the yellowing of the plastic shouldn't occur as LED's emit a much narrower spectrum of light (more visible light and not as much ultra-violet).
Tod From Denmark, joined Aug 2004, 1767 posts, RR: 3
Reply 7, posted (9 years 8 months 2 weeks 5 days 4 hours ago) and read 2234 times:
Quoting Warreng24 (Reply 6): Warm White florescent bulbs produce a "warmer" more reddish-yellow light. Cool White florescent bulbs produce a "cool" more pure "white" light. AirTran (as the OP mentioned) might prefer using the Warm White bulbs
Most operators chose warm white because they feel it makes that cabin appear less stark. CX is one of the few that go with cool white.
Quoting Warreng24 (Reply 6): As we move to LED based lighting, the yellowing of the plastic shouldn't occur as LED's emit a much narrower spectrum of light (more visible light and not as much ultra-violet).
And the LED systems allow for ajdusting the color as required.