Light reduction from using a filter

[metroplex]

How much light output is reduced from using a filter such as this:

http://www.showlenses.com/cart.php?target=product&product_id=16148&category_id=250

The application is the foglamp on 05-up Mustang GTs and I was thinking about using the yellow lens covers to distinguish them from the headlamps. I heard that these filters can reduce light output by 20-30%.

 

[2xTrinity]

That's probably fairly safe to assume. Naturally some light will be lost. In the case of the foglights though, many intentionally use yellow filters like this as the blue component of the light is what is most prone to getting scattered, and obscuring your view in the fog. So for actually using your fog lights in fog the filtered light should work just as well, maybe even slightly better. When it's not foggy, your regular headlights should still be sufficient.