It's not always interchangeable. A lamp is always a light, but a light isn't always a lamp.
Lamp is a funny word. I had to think about this for a minute. If I'm at the store I'm more likely to say "I need a lamp for my desk.", but at home I'm more likely to say "Turn on the light on my desk." In any event I should think "lamp" and "light" should be interchangeable in this instance, but I don't think duoLingo will agree.
You would actually say "I have a red light" to refer to your lamp (the sentence we have here)? I can't imagine phrasing it that way. A red light is the colour of a bulb, or a traffic light.
I don't know. Like I say the distinction between "lamp" and "light" is funny. When I saw this sentence: "J'ai une lampe rouge." I thought "douLingo is going to want me to call it a lamp, but it's not always a lamp. Sometimes it's a "light" " I had to think about it for a minute. Anyway. I would probably say "I have a red lamp on my desk.", but ask you to "Turn on that light (meaning the red lamp)." duoLingo doesn't accept "light" for any of the three sentences with "lampe" in this unit.
French has separate words for light and lamp, just like English. I think we have to translate each sentence as seems appropriate. Here, it's clearly lamp. I don't know what the other two sentences are that you speak of.
I agree that in English, you turn on a light, not a lamp. But in French, you don't turn it on, you light it, or illuminate it. "Allumer." If you imagine an old -fashioned oil lamp, you would light it. "Turn on" applies to an electrical light switch. The French verb is no doubt of far older origin than the English expression.
I just got back from Spanish duoLingo. There they accept queue for "cola". Now from my understanding a line is not always a queue, but a cola is always a line (or a tail). That is to say if a line of soldiers were marching down the street they'd be in a line (cola) but not a queue.