[lojban-beginners] Lightbulb

["Daniel Adamec" <dadamec123@gmail.com>]

What {sumti tcita} would be used for 'because' in a response to the query "why is the light bulb bright?". (apologies for the simplicity of the sentence).
I had thought {ri'a} because there are several physical causes (the switch being moved to the 'on' position, the electricity moving through the filament, etc.).
Also, because it is (presumably) a working light bulb and has a sufficiency of electricity correctly applied, there could be a certain amount of logic involved (perhaps including {ni'i}) (improbable but...)
 While I doubt that this is a correct usage, there is also a human factor, because had one not moved the switch, the light would not have activated (barring a house fire of several thousand degrees!!). 
I am probably making the problem more complicated than it really is, so once again I apologize for the simple explanation I will no doubt receive from several (rightfully) exasperated {jboprenu}
mu'omi'e daixel