2011+ IS models have a LED DRL instead of using a high beam bulb run at a low voltage as the DRL. I recently pulled out the high beam bulbs in my '12 IS and noticed that both high beam bulbs were covered with some brown stains on the bulb glass. These stains are indicative of a halogen bulb being run at a reduced voltage for an extended period of time. Everyone who owns a 2006-2010 IS will have high-beam bulbs that are stained brown if they leave their DRLs on, guaranteed.

But I have a '12 IS and the high-beams should be running at a normal voltage (12.4+) when on. I don't believe I have any wiring issues. Can other '11+ IS drivers check whether their high beam bulbs are similarly stained? I want to know if all '11+ IS models suffer from a lack of voltage reaching the high beam bulbs. If you don't use your high beams at all, then your bulbs should be crystal clear. If you use them frequently, as I do, then they should still be crystal clear, unless there's some sort of widespread issue among IS models with underfed bulbs.

 

Did you measure the voltage with the bulb in place?
Are you sure the deposits are not on the outside from contaminants (moisture) in the housing?

Toyota has historically used a voltage regulator to limit voltage to 12.3 / 12.5v as the peaks of say 14v that the charging system sees will kill a bulb fast. Over voltage kills a bulb much faster than under voltage. Under voltage <12v drops light output drastically while voltage of say 13.6v plus cuts the lifespan nearly in half.

9005 bulb is 12v/60 watts = 5.0A, while our battery off voltage is about ~12.9v but operating range is like 13.3 to 13.9v which is not 12 volts/60 watts the bulb is spec'd at.

When lit, some tungsten is shed from the filament and deposited onto the glass. As the bulbs hits nominal operating temperature, the deposits on the glass return to the filament so it can live on. Obviously over time not all of the tungsten returns to the filament and the filament weakens and breaks due to vibrations or initial startup when cold and the current is high.

In short low voltage typically doesn't do what you are seeing there.

 

Deposits are internal.

I will have to measure voltage drop at the bulb socket later when I have more time.

Chronically low voltage absolutely causes the browning of the bulb glass. I pulled a high-beam bulb from a family member's Toyota, and the glass was almost completely stained brown inside. That Toyota has high-beam DRLs, which runs the high beam bulbs at 6 volts (if I remember correctly).

The deposits on my IS bulbs are not returning to the filament. Some of them are remaining on the glass, which is indicative of a low voltage issue.