Throw or flood for mist/smog

The other morning there was mist everywhere, could only see 4 or 5 meters before everything disappeared in the white wall of nothingness...
It was too cold and so i did not bother going for my usual early morning walk, so I did not get a chance to test it but during the day as the sun slowly burnt off the mist I was wondering what you need in the mist...throw or flood?

What would work better, would the throw get absorbed by water vapour, or would the light pierce the smog, or would something that lit a big area be better, just for general walking, not driving mind.

I find throw works better, my L1 is my best light for heavy fog....but still not that great.

Incandescent light with pin point throw.

An aspheric mag might be the best. Something with a tight beam, but very little to no spill. I found my DBS cuts through fog fairly well.

Flood will just get soaked up by the water vapor and often will cause glare which will make it harder to see. A tight, intense beam works best to cut through the fog without blinding you.

stitch_paradox said:

Incandescent light with pin point throw.

Click to expand...

Like a Princeton Tec Tec 40!

Throw. Flood will reflect back and wash everything out.

The stock answer is a tight beam, but how far do you need to see to walk around? A flood light is generally much more useful for walking around in my opinion, so if you can see far enough with a floody light, I would recommend that as a walking light (but I prefer flood to throw in general anyway).

Actually, "throw" is not quite the correct term since even a light with great throw can have a big spill beam that creates a lot of glare in fog when you're trying to see something in the distance. To be more precise, you want a light where all the light is concentrated in a tight beam, like any of the lights designed with fire fighters in mind like the Streamlight Survivor. Also, how you use the light makes a difference, too. Holding the light away from the axis of your line of sight helps minimize the glare thrown back at your eyes.

Aspheric mag or Pelican Recoil LED series.

Tight beam and lower frequency of light.

Tight beam lessens the back scatter and lower frequency gets reflected less and won't blind you as much.

From my experience, it depends on what you're looking at, how far away, how much you want to re-aim your light, etc. If you're going for distance, a floody light is going to light up way too much of the mist between you and your target. But if you're primarily needing to see the path directly in front of you, and only occasionally wanting to look in the distance, flood is fine.

All the points that others have posted have essentially been true for my experience as well. Tight beams with relatively little spill will likely serve you best in most misty conditions. The one other thing that I've found key (perhaps even more important than the characteristics of the beam) is where you position the light. From my experience, the greatest portion of reflected light in mist is going to go almost directly back in the direction that it came. Thus, if your eye were right next to the flashlight, you'd have terrible visibility, whereas if your friend had the light and were standing six feet off to your side, you'd be MUCH better off. This means that in fog/mist, you'll probably want to avoid the fairly typical tactical-style grip, where you have your thumb on the light's tail, and you're holding the light at face- or shoulder-level. Instead, you'd want to hold it, say, like you would a 3D MagLite, when your thumb would be on the switch (thus, with the head sticking out the thumb/index finger end of your hand) and your arm hanging directly down.

Whether a beam is tight or floody (for example, a SF L1 either without or with a diffuser) has made less difference to my visibility in the fog than how I position the light relative to my eyes.

If I remember correctly, an old army trick used to be to use a blue filter in foggy/misty conditions.

Generally a "throw" light will work better for you. It doesn't have to be a super narrow angle neecssarily, the key is that there be as little spill as possible -- this is the main theory behind vehicle fog lights, they are positioned low to the ground -- so that the backscattered light won't dazzle the driver, and they direct the light low to the ground. They are not "pinpoint" lights, either.

The biggest reasons why incans are generally better suited is because of the way their filament emits in all directions, as opposed to into a ~150 degree forward angle, nearly all the light is capture as part of the beam, with relatively little spill. LED lights are the opposite, most actually transmit more light as spill than as part of the main beam. In a foggy situation, this creates two main problems:

1) the target isn't receiving very much light as a smaller fraction of the total lumens are captured in the beam
2) the greater percentage of the spill gets back-scattered by the fog, obscuring the target

Now, LED lights that use TIR optics I find work fine, this is because they have almost no spill. The wavelength/ color temp is not nearly as significant as beam profile for fog.

and lower frequency gets reflected less and won't blind you as much.

Click to expand...

Sorry to nitpick on the physics here, but there are a few things I'd like to clarify:

I believe you mean lower wavelength (eg "bluer" light), instead of frequency. Either way, in the case of rayleigh scattering, or scattering off the air molecules themelves, blue is scattered more -- that is why the sky is blue. However, that effect only applies when the particles doing the scattering are smaller than the wavelength of light.

Water droplets in fog, which are much larger than the wavelength of light, reflect all colors indiscriminately.

However, for practical purposes, very cool white LEDs are still typically worse in fog for the following reason:

1) our eyes are more sensitive to shorter wavelength light in the dark, so the dazzling effect is worse
2) most objects in nature, such as trees, dirt etc. absorb blue. ie, if you were to use a monochromatic blue light, it would be useless as just about anything you try to look at will only reflect very little of that light, but the fog would reflect just as much of it as with any other color.

If the fog is too thick, no amount of flood or throw will penetrate it. In fact it will shine back as an intense hotspot in the air.

Now if there is some visibility through a less dense fog where some details can be made out, then I would go with an incan with at least 100 lumens over an LED which will reflect most if th light back to you.

My SureFire M3T is my current light that seems to punch through the fog, rain, and snow better than my other lights. My M3T seems to have a less stippled reflector which helps in the throw department than my M6 which is has more texturing to it.

Also, don't hold the light at eye level.

Get an incandescent or an aspheric LED Mag.

My personal experience is that an LED with a focusing optic that eliminates the majority of the spill works well, while a ROP Low in a smooth reflector works even better .

WadeF said:

An aspheric mag might be the best. Something with a tight beam, but very little to no spill. I found my DBS cuts through fog fairly well.

Click to expand...

+1 on the DBS,I found that also.

This question reminded me that Lumaray's FL6 and FL12 have recently been upgraded to use the Nichia GS emitters for 2008. I don't think the FL6 "fog" head has been upgraded, though.

But even with the normal heads, the focused beam of the FL6, or the FL12 with the flood emitters turned off, seem like they would produce a beam suitable for distance spotting in fog because there is little spill. Plus, you have a totally watertight light for those misty, wet nights in the fog.

Always been intrigued but never pulled the trigger on the Lumaray before, but with the Nichia GS's, I'm getting a bit closer. However, not sure how they come up with their lumen figures, though. E.g. the FL6 has six GS's, which output about 10 lumens each. How do they come up with 150 lumens? Overdriving?

The light that works best for me in fog has been an Inova X02. Anything with a good optic with no flood light works best.