If something has a 1 in x chance of happening, if you do it x times, you have a 63% chance of hitting it at least once. So after 18,595 years, at 60 fps, you would have a 63% chance of hitting it at least once.
Anyway, every spark has about a chance of 0.0000000000002273737 % to reach the end. The framerate of 60 fps and the fact that one spark is generated every 8 frames means we have 60/8 = 7.5 sparks per second. So if we know that, on average, one out of every 2^42 sparks hit the light, we just have to divide this number by 7.5 to get the number of seconds that pass, on average, until the spark hits the light. This works out to 18-thousand-whatever years.
For the actual math you requested... The spark has 1/2 chance to travel left. If we assume it did travel left, it has 1/2 chance to travel left even more. By now, it has only (1/2)^2 = 1/4 chance to be where it is. Three times is (1/2)^3. And so on. 42 times is (1/2)^42 ~ 2.274 * 10^-13. It does not matter if it has to go left or right, it has to take one exact predetermined path, and the probability to hit it exactly with 1/2 a chance to miss every single step is minuscle.
Also, I used the framerate to estimate the time required to win this game, it is needed to calculate the number of tries per second.
If I understood you correctly, you assume that the spark is equally likely to hit ANY of the outputs. This is NOT so. It hits them in a gaussian distribution, meaning the middle ones are the likeliest to be hit, the outer ones the least likely. This is because to hit the outermost output, the spark has to travel left EVERY time, it cannot go right even one single time. It cannot get back if it does.
So it's impossible to calculate the exact probability.
Due to pseudorandomness, the probability for a win will be somewhat off, because the random number generator isn't 100% random.
it is also the same as binary number consisting of 42 ones. (or howmuch ever there are steps i lost count)
isnt it 1 in 2^42? 1s step is 1/2 if its true 2nd is also 1/2 together 1/2 * 1/2 = 1/4 and so on. length of the side is irrelevant to probability here.
1 in 82,944. if anyone can prove those odds wrong with actual math I encourage you to do so