I think the light stuff is about not starting of extinguishing fires, and electric lights are considered "fire" to ultra Orthodox Jews. So turning the light switch on is starting a fire, and turning it off is extinguishing one. The oven thing could also be to do with that, as anything that produces heat could also be seen as starting a fire. 5 seconds of research that I did states:

In addition to the general forbidding of all manner of work on the Sabbath, there is a special prohibition against making a fire (Exod. 35:3). The Rabbis considered this to include everything that pertains to the kindling of light, even if no actual work is involved. In modern times, there is a controversy regarding whether the switching on of electric lights and appliances is equivalent to making a fire.

...Orthodox Jews do not use electric appliances on the Sabbath, believing that the prohibition against kindling a fire was not based on the physical effort involved in rubbing two stones together to produce a spark but rather on the thought and planning that resulted in its generation.

For the Hazon Ish, the activation of an electric current and its transmission to sources of power, heat, and light that is produced by turning on a switch is forbidden because it falls under the category of “building” — intentionally causing something to happen. An exception is the refrigerator, which may be opened and closed because any electric current that this produces is incidental and without conscious intent. However, many observant Jews unscrew the refrigerator bulb for the Sabbath.

Lights that have been kindled before the Sabbath, such as the Sabbath candles, are allowed, as are an oven for keeping previously cooked food warm and a burner to keep water warm for coffee or tea. Similarly, it is permitted to leave an electric appliance running during the Sabbath and to use a timer to automatically turn an appliance on or off, as long as the timer is set before the Sabbath begins.

Exodus 35:3

You shall kindle no fire throughout your settlements on the sabbath day.