stop/tail light single filament question

[Cyrus]

On my daily drive ( vaux ashtray) it has single filament 21watt rear bulbs ( as per t25) but this is used for stop/tail light, dual brightness.
I understand that the car electronics must put in a lower voltage for the tail light and then full 12v for stop light. But does anyone know what voltage would be put into a 21watt bulb to make it equivalent to a 10watt tail bulb?

[California Dreamin]

On my daily drive ( vaux ashtray) it has single filament 21watt rear bulbs ( as per t25) but this is used for stop/tail light, dual brightness

Seems Vauxhall use some sort of adaptive lighting system on some models that varies the intensity of the bulbs.
I read some reference to 'pulsing' to control intensity.

Adaptive brake lights are a clever touch with this Vauxhall and the intensity of the three red rear lenses increases depending on the pressure applied to the brake pedal.

First I've heard of it...
Martin

[Cyrus]

It's an astra h 54 reg. It confused me when my tail light failed and only fitted a single filament. Like you say I could of missed a bulb in there but I'm pretty certain it had 5 21watt bulbs, stop, tail, rev, fog and indicator.

[Cyrus]

The reason I asked in the 1st place was I`m thinking of incorperating it into the T25 stop light to have it as a tail/stop light.

[Ian Hulley]

The tail light bulb should be a lower wattage than the brakelight and the fog light bulb, that's why they are normally 5/21w twins and a 21w for the brakelight.

Ian