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I'd be very interested to know if anyone has definitive advice on which types of light bulbs are considered an issur d'rabbanan (Rabbinic prohibition) vs an issur d'oraita (Torah prohibition) to turn on on Shabbat. This is a great discussion forum, and this is my first posting.

I've read various articles and asked some sheylot about it, but it seems the answer depends on technological issues, which themselves are not so clear cut.

The categories of light bulbs currently on the market are:

Incandesecent

I understand that these are an issur d'oraita because of they involve heating a filament till it glows.

Compact fluorescent lights (CFLs)

Apparently these are less of a problem than incandescent bulbs, but some compact fluorescent bulbs use a starter that requires a glowing filament.

The situation is complex because there are sub-types of CFL, including the following (see also the above link)

(1) instant-on; and (2) cold-cathode

The above 2 types may use a different filament (or no filament), so maybe they are less of an issue (or perhaps they still use a hot filament.. one really needs to be an expert in the technology to understand!).

In general, it seems that if a bulb does not reach 'yad soledes bo' temperature then it would not be a Torah prohibition? However, the average 60W equivalent compact fluorescent bulb gets too hot to touch, so is that a problem?

LED bulbs

These should be less of a problem d'oraita, as they don't work by means of a glowing filament. However, they apparently can get very hot because the electronic circuit board that runs each bulb can generate a lot of heat, at least with the brighter types. Do they got so hot that they are a Torah prohibition?

Please correct me if my assumptions are wrong. I'd be very interested to hear any definitive views on this. Thanks!

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Hi, welcome to Mi Yodeya and thank you for sharing this enlightening question with us! You should consider giving yourself a username more meaningful than 2503. I hope to continue to see you around. –  Double AA Mar 11 '13 at 5:45
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Could you clarify what you're talking about? Lights are not an isur (prohibition) at all. Are you referring to lighting them on Shabas? Extinguishing them on Shabas? Lighting them on yom tov? Extinguishing them on yom tov? Using them to cook milk and meat together? Something else? Please edit this into the first part of your question to clarify it. [continued in next comment] –  msh210 Mar 11 '13 at 5:58
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[continued] As the question stands now, "It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete" and I'm closing this for that reason. I'll be more than glad to reopen it when the question is clear as to what it's asking. –  msh210 Mar 11 '13 at 5:59
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@msh210 he had tagged it Shabbat! –  Double AA Mar 11 '13 at 15:10
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Given the edits, I'm reopening. –  Double AA Mar 11 '13 at 16:10

2 Answers 2

Here is an article by Rabbi Michael Broyde & Rabbi Howard Jachter that discusses the entire topic: http://www.daat.ac.il/daat/english/journal/broyde_1.htm

(side note regarding heating a bulb before it becomes yad soledes- just because the glass encasing of the bulb isn't yad soledes doesn't establish that the filament itself is not.)

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Based on my knowledge, I would say that even if you would say that since light bulb filaments get hot, it would only be an issur drabonon. This is because you aren't heating the filament with intent to mold the metal into a shape like a blacksmith rather you are heating the metal filament for light, the case now becomes a מלאכה שאין צריכה לגופה.

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