In places were candles are unsafe or prohibited from use, could light emitting diodes with batteries substitute? Closing the circuit would be regarded as work. But so is lighting a candle for any other purpose but the blessing. Could an analogy of kindling a candle be applied to activating the substitute to honor shabbat only?
Yes you can light shabbat "candles" using battery powered flashlights. Some rule you can even do so using electric lights (although others disagree).
Here is one source
Hacham Ben Sion, in his work Or Le'sion (vol. 3, p. 189, and vol. 2, 18:13), writes that one does not fulfill the obligation of Shabbat candles with electric lights because the "fuel" is not present at the time of lighting. When a person lights a candle, all the wax or oil needed to sustain the flame is already present. An electric lamp, however, is sustained by the electric current that is constantly being fed into the lamp. Since that current is not present at the time of lighting, one cannot use such a light for this obligation. Hacham Ben Sion contends that this would be analogous to an oil lamp that has just several drops of oil, and into which one slowly pours oil drop by drop. Clearly, one cannot recite the Beracha over lighting in such a fashion, since the fuel needed to sustain the flame for the required period is not already present. Likewise, according to Hacham Ben Sion, one cannot fulfill the obligation of Shabbat candles with an electric light.
Of course, if we follow this rationale, we would allow using a battery-operated light for this Misva. As Hacham Ben Sion notes, in the case of a battery-operated light all the power is already contained in the mechanism, and it would therefore suffice for the obligation of Shabbat candle lighting.
Hacham Ovadia Yosef, in his work Yabia Omer (vol. 9), disagrees, and rules that in principle, one can, in fact, fulfill the obligation with electric lights. Since when all is said and done electric lights have the effect of providing illumination, they suffice for this Misva regardless of the fact that the source of power is not currently present.
This ruling has numerous ramifications. For example, if a person spends Shabbat in a hotel or hospital, where he is not permitted to kindle a flame, he may turn on an electric light before Shabbat in fulfillment of the obligation to light Shabbat candles. (Rav Aharon Kotler is likewise reported to have taken this position.)
and here from Ohr (!)
Most Poskim, therefore, say that you may use electric lights and even recite the blessing over them, since they add to Shalom Bayit and Oneg Shabbat the same way as candles.
Some Poskim, however, differentiate between battery-powered lights, such as flashlights, and those that run on electricity generated from a power plant. Battery-powered lights are all right since they contain 'fuel' - i.e., the battery - which is right there when you light it. Regular lights, on the other hand, have no 'fuel'. Rather, the electricity is 'piped' in from the outside; and furthermore, the electricity doesn't really exist yet - it's being created every second at the power plant. In a sense it's like lighting a wick with no oil. It's known about Rabbi Moshe Feinstein, zatzal, that once when he was in a hotel and unable to light candles, he 'lit' a flashlight and made a blessing over it.
- The Radiance of Shabbos, Rabbi Simcha Bunim Cohen
- Shmirat Shabbat Kehilchata 2:43, footnote 22
There is a question of what type of lightbulb qualifies, and whether a traditional incandescent lightbulb is required (because it is closest to fire) or whether fluorescent (and presumably LEDs) would suffice. In an extensive review of sources R Howard Jachter and R Michael Broyde conclude that fluorescent lights are permitted for shabbat candles in cases where candles are not possible, based on R Ovadia Yosef and R Neuwirth (same sources as above).
As always CYLOR before using this in actual cases.