Re: standing behind a window - the same as sunbed??
I don't know if standing in front of a window is something you should consider. Sunbeds are lit by UV light bulbs, and the amount of exposure you get is equivalent to spending 8 hours in the summer sun. If you stand in front of a window, you'd be getting indirect sunlight that may or may not be as strong as the sun in the summer. I know people that ski a lot get tanned from the reflection of the winter sun off the snow, but in terms of the length of time you'd need to be in direct contact with the sun, I couldn't know. You could TRY, I'm fairly sure that you wouldn't burn... But I don't know if you'd get any color at ALL. Maybe you could consider a bronzing powder, or spray-on-tans if you want a little glow?