Turn left on green

[rawonam]

On intersections with two lights (main (round) and left arrow), am I allowed to turn left (giving way to opposite traffic) if the main indicator is green and the arrow is red? Someone told me that it was possible, the only functionality of the arrow is to tell you that the opposite traffic has red light.

If the main indicator would show an arrow (forward) it would be clear, but as it is the situation is ambiguous.

[onkko]

No. Red arrow tells that you may not turn to left. If there is not a red arrow and only green arrow then you may go and "someone" is right.

[riku2]

Someone told me that it was possible, the only functionality of the arrow is to tell you that the opposite traffic has red light.

That applies to the green arrow (showing you that you can turn across approaching cars since (invisible to you) they have a red light). But not a red arrow, that must always be obeyed if you are turning.

There are various configurations of lights

1. only circular traffic lights
2. circular traffic lights + left turn green arrow light
3. circular traffic lights + left turn green arrow + left turn red arrow (and probably left turn amber)

In #1 you always give way to oncoming traffic if turning left across them. In #3 you always obey the arrows that apply to you and when you have green the oncoming cars will have red as part of the cycle.
#2 means you can turn across the oncoming cars if you have a green arrow but otherwise wait for a gap, sometimes the green arrow is part time (rush hours only) or comes on later in the cycle (so before the green arrow some cars can cross if there is not much oncoming traffic).

What is common in finland is scenario of lights like #1 but the oncoming cars will have a red, so you CAN turn across them, but for various reasons (saving money? changing the cycle later and not upgrading the lights?) the green arrow light is not installed. You have to learn which intersections these are based on previously observed behaviour of oncoming cars. This is obvious if they stay stopped and your lights go green, but not so clear if a car is coming towards the lights opposite and you don't know if they will stop because they have a red light or not. If you stop then regular drivers behind you are likely to crash into the back of you (since they have learned oncoming cars have red when you have a green).
This kind of lazy - learn intersections over time - design method is common in Finland and not just regarding traffic lights. When you have low traffic volumes you can get away with poorly designed junctions like this.

[rawonam]

Thanks a lot! Now it's much clearer.