Confusion about Halogen UV filtering

[Pspboy17]

I was looking into swapping the sockets on a lamp to G8 so I could use common halogen bi-pin bulbs. I'm slightly concerned about running these bulbs without a UV cover since all my halogen lamps have a cover, but I haven't been able to find how important it is. This little segment on wikipedia sounds like common bulbs should have glass that filters UV?

High-temperature filaments emit some energy in the UV region. Small amounts of other elements can be mixed into the quartz, so that the doped quartz (or selective optical coating) blocks harmful UV radiation. Hard glass blocks UV and has been used extensively for the bulbs of car headlights.[24] Alternatively, the halogen lamp can be mounted inside an outer bulb, similar to an ordinary incandescent lamp, which also reduces the risks from the high bulb temperature. Undoped quartz halogen lamps are used in some scientific, medical, and dental instruments as a UV-B source.

But after looking a bit more I'm not sure. Satco sells some bulbs which are advertised with uv blocks, and many that don't say anything about filtering. Was hoping someone could clear this up for me, I would be sitting very close to these lights.
https://www.satco.com/s3542.html

Thanks

 

[ebuchner]

Often times, yes, the lamp envelopes themselves will pass UV if the envelope is undoped fused quartz which is very common. The reason you're seeing some that say they don't emit UV is because it's either quartz doped with a bit of cerium oxide, which allows it to block UV, fused quartz with an external UV blocking coating applied, or because it's a highly refractory aluminosilicate glass which inherently passes very little UV.

It will be non-obvious which is which unless it's clearly labeled, so for your purposes just go with whatever has a label explicitly mentioning a "UV coating feature," or is filtered or something like that.

 

[Pspboy17]

Often times, yes, the lamp envelopes themselves will pass UV if the envelope is undoped fused quartz which is very common. The reason you're seeing some that say they don't emit UV is because it's either quartz doped with a bit of cerium oxide, which allows it to block UV, fused quartz with an external UV blocking coating applied, or because it's a highly refractory aluminosilicate glass which inherently passes very little UV.

It will be non-obvious which is which unless it's clearly labeled, so for your purposes just go with whatever has a label explicitly mentioning a "UV coating feature," or is filtered or something like that.

Thank you. I might pick up a uv test card just for peace of mind. Is there a reason why no uv blocking would be desirable? Kinda strange to me that's it's not just a standard coating.

 

[ebuchner]

There are a few reasons for this. I'm sure there's a correct ranking of importance for them, but I haven't been able to dig deep enough into the technical history to be sure of them yet. So in no particular order:

a) The fact that they can emit UV is an advantage in applications where you're using the output of the source to cure UV sensitive resins and coatings. Why use a specialized mercury discharge source when a simple incandescent source will suffice?

b) Projectors and DJ lights have heaps of optics between the lamp and the outside world. Almost invariably, the lenses found in these optical systems are made of glasses that contain non-trivial fractions of boron oxide, sodium oxide, aluminum oxide, etc... The addition of these oxides improve workability of these glasses so they can be processed at lower, more friendly temperatures during manufacturing. Coincidentally, the addition of these oxides give them UV filtering properties, so why filter the lamp when everything between you and it will?

c) Tradition. Manufacturers invested lots of time and money into developing metal-to-fused quartz seals for electrical leads beginning around the 1950s. Using different envelope materials (even quartz with just a dash of titania or ceria to filter UV) throws uncertainty and a little bit more cost into process control. In a production environment with lines dating back decades that's not a risk that *everyone* is going to take, although obviously plenty of manufacturers figured it out just fine.

 

[PhotonWrangler]

Thank you. I might pick up a uv test card just for peace of mind. Is there a reason why no uv blocking would be desirable? Kinda strange to me that's it's not just a standard coating.

I highly recommend the UV test card, especially if you're going to be working in close proximity to a halogen lamp for extended pe4riods of time. A decent UVA/UVC card is only around $10-$20.

 

[JoakimFlorence]

It very much depends on the situation. In some cases it might make almost no difference at all. In other cases it could be a big cause for worry.
It will not have a greater percentage of UV than sunlight.

If it's going to be a work lamp and you will be up close, or examining things under a high degree of illumination from the light, then it could be a cause for worry. That UV is not good for your eyesight.
I would not advise unfiltered light for reading, for long periods.

If there are things (like antiques) in the room that you are worried about fading or light damage over time, then there should be a filter.

If, on the other hand the light is at low to ambient levels, and just in the background, especially if the light is directed up at the ceiling and diffuse, and you do not spend very much time in that room or are not too close to the light, then it would not be something to worry about.

I also doubt that unfiltered halogen is much worse than bare exposed fluorescent or metal halide lamps (though those are not good, in my opinion).

For portable lights (flashlights), in most cases it will not matter. Though probably a good idea not to shine the light directly into people's eyes for too long.