1998 - 2000 LS400 uses a secondary 5 watt T 3-1/4 bulb which protrudes into low beam reflector of headlamp assembly.

This secondary bulb illuminates when the low beams are turned on (at stalk), but not for daytime running lights.

So when a primary low beam expires you remain visible to other drivers and avoid probable cause stop by officer friendly.

Left and right lamps were burnt out, so acquired new bulbs from Lexus.

Worth checking and replacing.

Lamp replacement requires removal of air filter box and battery...if not dexterous.

Just recovered 5W of illumination...

LEDs would work well in this application as this circuit does not trigger a bulb failure indicator.


Bulb is item 8160F in exploded diagram


Image of low beam reflector taken through plastic headlamp lens.. Upper top left depicts cutout where secondary bulb resides.

Secondary bulb illumimated in slot. Picture taken daylight

 

It is my understanding that they are the park lamps aka city lamps. I replaced mine by taking out the head lamp assemblies (3 bolts, 1 nut). The front turn signal has to be removed to access 1 of the bolts and the nut. There is a Phillips head screw that has to be removed to get the turn signal out, then the assembly is pulled forward—this can be tricky though. I used a homemade tool to make extraction easier (see pix). Never thought about them being a back up system, thanks for pointing that out!