Condensation keeps forming inside this 400 watt metal halide flood light, anytime its on for a while and then I turn it off condensation forms inside, I think its due to the temperature difference inside and outside the fixture so if anyone has any idea on how I can stop this from happening please tell me.


Thanks

Perhaps very steamy in your area (Humidity of 80% and over).

I see it sometimes and I can't stand it

Toss a bunch of those silica packets from beef Jerky bags inside the light.

If fogging or a visible condensation appears on the lens AFTER you turn it on, it means there is water trapped somewhere inside of the fixture. Normally humidity from the outside does not condensate in a lantern. When it is off, there is no reason to pull it in. When it is ON, it gets warmer than surrounding, so the relative humidity will always be way below 100%, so it can not condensate. So the only thing remaining is water trapped inside (very likely either pooling in some area exposed to the ballast or lamp heat, or soaked into the ballast), so once powered on, it evaporates from there and then condenses on the coldest surface within the lantern: The lens. After powering down, all temperatures equalize back, so the greater affinity of the ballast materials to the water means the humidity gets absorbed back.

So what to do:
First you have to find where the moisture resides, mainly when the thing is OFF. And so get rid of it (pour it away, dry with towel, in case it is absorbed within the ballast, bake dry them - 100degC for an hour or two in a hot air oven for the ballast,...). Alternatively you may just keep the lantern ON with the bowl open, provided the lamp is open rated or there is nothing underneath that may catch fire should the lamp explode (although not related, any time you run a lamp, it may fail catastrophically, so you should always take that risk into consideration).
Then look for is how the water got in in the first place. Is the weather seal compromised somehow? Through the pole? Were some components (mainly the ballast) exposed to elements (so allowed to absorb the water into their structure - mainly the coil/transformer ballast part) before assembled into that lantern?

The silica gel from a chip bag (or anything else) won't do a thing, because once you open the package where ir is, it stsrts to absorb humidity from the air around and saturate pretty fast. You would have to regenerate it (dry it out) first, e.g. in the hot air oven at 100degC. And even after that, the capacity to absorb water is rather limited, the small packets you found in the bags are designed to absorb just what had diffused in. If you look to big truck air brake systems, there is about 1kg of the silica gel and it is supposed to dry out just one cycle of the pressure governor (compressor topping up the system, so about 100 l of air) between each regeneration cycle (when not pressurizing, the compressor just warms up the air and pushes it through the dryer can to drive the absorbed moisture out by that hot air). So when a 1kg of the silica gel is good for barely 100 l of air, the few gramm packets won't do anything except just really residual moisture in already dried out container.

I had some condensation form inside one of my AJ Ferguson Zodiacs. All I had to do to fix it was slightly loosen the retaining nuts for the diffuser so that the heat could escape. Since doing that, the issue has gone away. I have the light installed indoors so there's no issue with rain getting inside.