Um ... one "light year" IS one earth year, but it's also the DISTANCE light travels during that one year.

It depends on how fast you travel. If you travel at the speed of light it would take 1 year.

One if travelling the speed of light, much longer if not you need to give a speed to get the answer.

1 year.

For WHAT to travel one light year? The term "light year" is a distance quantified in terms of time, because it's easier to think of such vast distances this way. Specifically, it is the distance light travels in a vacuum in one standard Earth year (planetary orbit around Sol). The speed of light in a vacuum is 299,792,458 meters/second (exact), or approximately 186,282 miles/second, or 670,615,200 MPH (give or take a smidgen). If you do the math, this works out to a distance of roughly 9.46 X 10^12 kilometers, or 5.88 X 10^12 miles. So if you are talking about something moving at the speed of light, then it would take one Earth year to travel a distance of one light year. For anything else traveling LESS than the speed of light, the time required to cross that distance would be proportionately longer than one Earth year. For example, if you were in a car driving 100 MPH, it would take you 6,706,152 years to travel a distance of one light year. The Voyager 1 probe, on track to exit our solar system and enter intersteller space, is currently traveling at about 17 km/sec, or about 38,000 MPH. If it maintains this velocity, it will take Voyager 1 about 17,648 years to travel a distance of one light year. I haven't double checked my calculations here (I leave that up to you), but they are probably fairly accurate. If you find an error, I'll happily edit my answer!

Two years at half the speed of light.

at what speed? for an electron moving at the speed of light, it would take 1 year. for anything else traveling slower, longer.

If your question is, "How many Earth years does it take for THE EARTH to travel one light year around the Sun?" ... my calculations indicate it takes about 44 Earth years plus 5 Earth months and a fraction of 1 Earth day. So ... when you turn 44 years + 5 months old, you can celebrate having travelled 1 lightyear around the Sun since birth (a.k.a. 1 lightyear old, in reference to the Sun)!!! Obviously, the Solar System, Milky Way, etc. are also moving, so you might be 1,000,000+ lightyears old in reference to some other star or black hole out there ... but the Sun is the most logical reference point for us Earth-dwellers! Thankfully, I haven't yet reached my 1st lightyear birthday ... apparently, my grandmother will turn 2 next year!!!