Fogging lenses?

Recently, with me adding a number (4) of high power (2.5a+) XM-L P60 drop-ins to my line-up I've been noticing a few of my lights seem to fog up when used on high for a time outside, especially if cold/windy.

I understand this is due to the humidity in the air being driven away from the heating reflector and eventually ending up condensing on the coolest part of the light, which on a cold night is the reflector. I have tried to eliminate this by opening the light and leaving it outside on the lowest humidity time/day I can and trying that night to see if it fogs.

This has improved it, but when colder nights come it still doesn't seem to work completely, and I have ended up in what seems an endless cycle of re-opening just to try and lower the humidity of the air inside the head every day only to find it hasn't worked at night. :hairpull:

Does anyone know of any better/more effective ways to stop fogging of the inside of lenses on high power lights?

Thanks,

RF

I don't know the answer, but have noticed this in my Fenix TK35. This light drives an XM-L really hard.
I tried to unscrew the module in the bezel to gain access to the reflector and lens in case they weren't screwed in airtight.
Unfortunately the module is threadlocked and all I ended up doing was scratching around the dimples in the module with my circlip pliers.

One of my first ROPs did the same thing. The lens would partially fog up. I finally disassembled the light and left it in the sun and wind for a day, then I ran the light without the head, then finally used a hair drier to finish off whatever the sun and wind had missed. No problems since. Can't explain it....but it worked.

You just need to clean the inside of the lens. Warm air can hold more moisture than cold air (hitting the cold lens). If there are particulates on the glass the fog forms. If there are no particulates it doesn't form.

In diving when we either spit on or use a commercial preparation on the inside glass of our masks before submerging this is what we are doing...cleaning the glass to prevent fogging during the dive.

In the winter in your house if your windows are clean generally they don't fog but if you go and put your fingers on the glass pretty soon water droplets will be running down the window.

Thanks, I hadn't considered particulates on the inside of the lense as a problem before.

I do try to keep my lenses as clean as possible though, and the more powerful ones still fog up..

.....

A large 'air tight' storage box from a supermarket, fill with rice to create a bed for your flashlight. Take it apart as much as you can sensibly do so. Leave it for a few days in the box.
If this doesn't dry it out, repeat. If it still doesn't dry it out, cook and eat the rice in protest.

Thanks, I never knew about the saliva thing, I'm not sure I should go spitting on my lenses though.

I had also considered the rice box method, but worried that as I would have to remove the light from the box to re-assemble, wouldn't it just re-fill with more humid air again?

.....

RedForest UK said:

I had also considered the rice box method, but worried that as I would have to remove the light from the box to re-assemble, wouldn't it just re-fill with more humid air again?

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Nottingham is that humid?
I guess you'll have to wait for a dry spell like the drought we're been having

I've had an eBay Chinese P60 SST-50 dropin fog up in a light, I felt it was possibly the 18650 battery venting. When I opened the light, the dropin was uncomfortably hot. I tried tightening the thermal connections with a larger spring and some thermal grease but the result was the same. I parked the dropin in a drawer for safety reasons.

Size15's said:

Nottingham is that humid?
I guess you'll have to wait for a dry spell like the drought we're been having

Click to expand...

Ha ha it's not that bad :nana: But if the air that's in it now is too humid for it then I mean even after drying it would end up with similar air in it again before it was reassembled..

I don't think the mist is a safety issue, just a natural side effect of a drop-in getting hot.

I'll have to go on the look out for some anti-fog spray I think.

This may be as simple as a leaking o-ring or boot. I'd try replacing all o-rings, properly lube them and replace the boot or at least tighten if possible. I know, you haven't been diving with the light, but airborne moisture is somehow getting into the light. Just need to seal off points of entry. That's my 2 cents. :wave: