Glare reduction on OEM foglights

The problem:

The OEM reflector based foglights on the Prius throw a lot of stray light, AKA glare, up above the cutoff level of the lowbeam headlights even when the reflectors behind the bulbs are adjusted to their lowest setting.

To verify this, park facing a wall about 15 - 20 ft. away with your headlights (lowbeams) on. Turn your foglights on and off and you will see a distinct difference where the foglights are illuminating the wall above where your lowbeam headlight cutoffs are delineated on the wall. That extra light above the lowbeam cutoff is glare to anyone approaching you from the opposite direction, and defeats the purpose of having "foglights", which are supposed to reduce the amount of light projected up, which is reflected back by fog/mist/snow/dust/rain, etc. back into your eyes at night, reducing your night vision.

The NHTSA is aware of the glare problem, primarily due to receiving numerous complaints from motorists:

See section 2.4 in the document for specifics to foglights and other auxilliary lights.
NHTSA Notice: Glare from Headlamps and other Front Mounted Lamps - FMVSS 108


Lighting 411:



The diagram above (I didn't make it, it's good right? ) illustrates the major differences between a reflector based light and a projector type light.

The reflector type light (left, diagram) has only a couple of components: a light source, a reflector and a lens or cover. Even with proper design, some stray light will get reflected off the bottom of the reflector and shine out of the light at a high angle (glare). The diagram on the left omits the corresponding "normal light pattern" coming off the lower half of the reflector to better show the source of the stray light that causes glare. Also, there would be corresponding stray light coming off the upper half of the reflector, but that stray light would be directed down toward the ground in front of the vehicle.

The projector type light (right, diagram) has a light source, and a reflector as well. However, there is also a proper lens, which focuses the beam, and more significantly, a physical cutoff shield placed between the light source and the lens. This cutoff shield in the projector design gives the light beam a sharp cutoff pattern as long as the shield is properly designed and placed at the right distance from the light source and lens.


Glare reduction:

My goal is to try to mitigate some of the glare that comes out of the lower half of the reflector in the Toyota oem foglight. I will do that by placing some colored vinyl overlays over the bottom third or half of the foglight glass lens/cover (experimentation to follow). Some light output will be lost as the "normal light pattern" that is coming straight out of the bottom third of the foglight will be attenuated by the overlays, not just the stray light; however, most of this lower light beam is shining on the road right in front of the car anyway. If anything, it is causing more reflected light off the roadway as glare to oncoming drivers, a problem especially when the road is wet and it becomes a more reflective surface.

I have some light smoke vinyl and yellow smoke vinyl overlay material coming in soon. I am using yellow overlay because I have Nokya Hyper Yellow H11 halogen bulbs in my oem foglights. When I receive them, I will apply first the yellow overlay to the bottom third of the foglight cover/glass to see if the glare is significantly reduced. If not, then I will try the light smoked material. I may also try a double layer (light smoked + yellow smoked) if I have to, but I'm trying to avoid putting multiple layers of film over the glass foglight cover because I don't want to create a situation where the glass is retaining heat unevenly, which might increase the chance of heat/stress fracture.

Also, I may have to increase the surface covered by the film from the bottom third to half, depending on the results of my experiment.


Aesthetics:

It remains to be seen, how much the aesthetics of the foglights will be affected. It may look weird to have only a partial covering of the foglight outer glass covers. That's why I'm going to start off with the yellow film and try to avoid the smoke colored film. But then again, our Prius is dark gray (Winter Gray Metallic), so maybe the smoke film won't stand out as much as yellow... plus, I suspect, that the gray film will be more effective at actual glare reduction than the yellow film. Well, we'll see.

 

Reserved for results and pics of my experiment.

Hopefully success.

Or utter failure. ... stay tuned.

Edit: I forgot to mention in the first post that I am running non-standard H8 35w halogen bulbs with modified bulb bases in my foglights:



I had changed them from the standard 55w H11 halogen bulbs to reduce heat in the foglight enclosures, as well as using less power, when I was using my foglights as DRLs (Daytime Running Lights). I'm no longer using my foglights as DRLs, but I find that the 35w H8 bulbs still put out a lot of light. If my glare reduction experiment works well, I might switch back to the H11's, or not. I like the fact that the H8 bulbs run cooler.

 

In case anyone suggests getting projector type foglights... I tried getting projector type foglights for a proper cutoff.

The ones I got were admittedly cheap, and manufactured in China. Upon receiving them, I saw that they didn't have DOT or SAE on the outer glass covers, so they were technically illegal to use in the US of A. On top of all that, the cutoffs were really cr@ppy, especially for projectors, so they got returned.

In case anyone wants to know which ones they were, let's just say avoid projector type foglights with LED based halo rings on eBay.

There are true CCFL ring projector type foglights also available, but I never tried them, because I feared that the projectors in those lights would have the same poor cutoff performance as the ones I tried (also manufactured in China?).