Another random q (light wavelength) - Page 2 - SV650.org

tigersaw · 09-02-07, 07:22 PM

Cut from wikipedia:

LED light sources
Automotive headlamp applications using LEDs are not yet in volume production, but have been undergoing very active development, and present prototypes give performance roughly equal to existing halogen headlamps. These prototype designs currently require large packaging and a large number of the most powerful LED emitters available. As LED technology continues to evolve, the performance of LED headlamps is predicted to improve to approach, meet, and perhaps one day surpass that of HID headlamps. LED headlamps, foglamps and other forward illumination devices have so far generally been featured only on manufacturers' concept cars, but the first series-production LED headlamps will be factory-installed on the 2007 Lexus LS 600h / LS 600h L. They will also appear on the version of the 2007 Audi R8 sports car sold outside North America.

The limiting factors with LED headlamps presently include high system expense, regulatory delays and uncertainty, glare concerns related to the output spectrum of white LEDs, and logistical issues created by LED operating characteristics. LEDs are commonly considered to be low-heat devices due to the public's familiarity with small, low-output LEDs used for electronic control panels and other applications requiring only modest amounts of light. However, LEDs actually produce a significant amount of heat per unit of light output. Rather than being emitted together with the light as is the case with conventional light sources, an LED's heat is produced at the rear of the emitters. The cumulative heat of numerous high-output LED emitters operating for prolonged periods poses thermal-management challenges for plastic headlamp housings. In addition, this heat buildup materially reduces the light output of the emitters themselves. LEDs are quite temperature sensitive, with many types producing at 30° C (85° F) only 60% of the rated light output they produce at an emitter junction temperature 16° C (60° F). These needs, to exhaust heat from the headlamps and to keep LED emitter junction temperatures under control, require expensive powered ventilation systems.

Additional facets of the thermal issues with LED headlamps reveal themselves in cold ambient temperatures. Many types of LEDs produce at -12° C (10° F) up to 160% of their 16° C (60° F) rated output. The temperature-dependency of LEDs' light output creates serious challenges for the engineering and regulation of automotive lighting devices, which are in some cases required to produce intensities within a range smaller than the variation in LED output with temperatures normally experienced in automotive service.

Cold weather also brings another thermal-management conundrum: Not only must heat be removed from the rear of the headlamp so that the housing does not deform or melt and the emitters' output does not drop excessively, but heat must in addition be effectively applied to the front lenses of the lamps—which are not heated by the cold light beam produced by LEDs—to provide rapid and complete thawing of snow and ice accumulation.

LEDs are increasingly being adopted for signalling functions such as parking lamps, brake lamps and turn signals as well as Daytime Running Lamps, as in those applications they offer significant advantages over filament bulbs with fewer engineering challenges than headlamps pose.

09-02-07, 09:14 PM

Showing my age here...

About 15 (maybe slightly more?) years ago they showed this idea on Tomorrows World.

1st white coat with normal headlights,
Then reflective jacket with headlights (far in the distance from the first obviously)
Lastly normally dressed with UV light (far ahead of the reflective person)

Effect was amazing, but they turned the main lights off so you could see the UV illumiated person. Whether this was for effect, or due to the normal lights interferring somehow I can't remember.

Stu

I initially types 10 years there, then remembered I've nearly been out of the UK for that long!

Stu · 10-02-07, 12:38 AM

I take it your idea won't suffer from the following problem -
On full beam and come up to a large road sign that the reflection is so bright it affects your vision?

10-02-07, 10:01 PM

Quote:

Originally Posted by Stu

I take it your idea won't suffer from the following problem -
On full beam and come up to a large road sign that the reflection is so bright it affects your vision?

Nope, that thought struck me too a long while back. They will be powerful enough to give a glow, but not so powerful that any glare hinders vision.

That means I'll have to comprimise overall distance, but there's always comprimise to be made somewhere.

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09-02-07, 07:22 PM	#11
tigersaw Member Mega Poster Join Date: Mar 2005 Location: Llanwrtyd Wells Powys Posts: 1,146	Cut from wikipedia: LED light sources Automotive headlamp applications using LEDs are not yet in volume production, but have been undergoing very active development, and present prototypes give performance roughly equal to existing halogen headlamps. These prototype designs currently require large packaging and a large number of the most powerful LED emitters available. As LED technology continues to evolve, the performance of LED headlamps is predicted to improve to approach, meet, and perhaps one day surpass that of HID headlamps. LED headlamps, foglamps and other forward illumination devices have so far generally been featured only on manufacturers' concept cars, but the first series-production LED headlamps will be factory-installed on the 2007 Lexus LS 600h / LS 600h L. They will also appear on the version of the 2007 Audi R8 sports car sold outside North America. The limiting factors with LED headlamps presently include high system expense, regulatory delays and uncertainty, glare concerns related to the output spectrum of white LEDs, and logistical issues created by LED operating characteristics. LEDs are commonly considered to be low-heat devices due to the public's familiarity with small, low-output LEDs used for electronic control panels and other applications requiring only modest amounts of light. However, LEDs actually produce a significant amount of heat per unit of light output. Rather than being emitted together with the light as is the case with conventional light sources, an LED's heat is produced at the rear of the emitters. The cumulative heat of numerous high-output LED emitters operating for prolonged periods poses thermal-management challenges for plastic headlamp housings. In addition, this heat buildup materially reduces the light output of the emitters themselves. LEDs are quite temperature sensitive, with many types producing at 30° C (85° F) only 60% of the rated light output they produce at an emitter junction temperature 16° C (60° F). These needs, to exhaust heat from the headlamps and to keep LED emitter junction temperatures under control, require expensive powered ventilation systems. Additional facets of the thermal issues with LED headlamps reveal themselves in cold ambient temperatures. Many types of LEDs produce at -12° C (10° F) up to 160% of their 16° C (60° F) rated output. The temperature-dependency of LEDs' light output creates serious challenges for the engineering and regulation of automotive lighting devices, which are in some cases required to produce intensities within a range smaller than the variation in LED output with temperatures normally experienced in automotive service. Cold weather also brings another thermal-management conundrum: Not only must heat be removed from the rear of the headlamp so that the housing does not deform or melt and the emitters' output does not drop excessively, but heat must in addition be effectively applied to the front lenses of the lamps—which are not heated by the cold light beam produced by LEDs—to provide rapid and complete thawing of snow and ice accumulation. LEDs are increasingly being adopted for signalling functions such as parking lamps, brake lamps and turn signals as well as Daytime Running Lamps, as in those applications they offer significant advantages over filament bulbs with fewer engineering challenges than headlamps pose.

09-02-07, 09:14 PM	#12
MavUK Guest Posts: n/a	Showing my age here... About 15 (maybe slightly more?) years ago they showed this idea on Tomorrows World. 1st white coat with normal headlights, Then reflective jacket with headlights (far in the distance from the first obviously) Lastly normally dressed with UV light (far ahead of the reflective person) Effect was amazing, but they turned the main lights off so you could see the UV illumiated person. Whether this was for effect, or due to the normal lights interferring somehow I can't remember. Stu I initially types 10 years there, then remembered I've nearly been out of the UK for that long!

10-02-07, 12:38 AM	#13
Stu Trinity Mega Poster Join Date: Jun 2006 Location: Guildford Posts: 8,027	I take it your idea won't suffer from the following problem - On full beam and come up to a large road sign that the reflection is so bright it affects your vision?