

For most people the short answer is, mains power is so reliable that it’s not worth your bother to worry about the emergency situations. As long as things work, even a significant amount of inefficiency doesn’t add up. So stop worrying, just get things working.
If, on the off chance, you actually are using emergency power a lot, for whatever reason, then yes, this is a worrying about. In that case, you no longer want a short answer. You need a long, complex answer that covers all the different possibilities. So you need to start studying. Be prepared to spend months working at all the details for your specific situation.





The vast majority of blind people can see the sun. Blind really means that their vision is so bad that we cannot correct it to anything close to normal and not that they see anything at all. Each experience is different, but likely they can see enough that for purposes of your question they are not blind.