Just like when doing the button tutorial. The digitalwrite accounts for current by turning on a 20k resistor built into the arduino to limit the incoming current while reading the button press, though in your case its the LED that its reading a signal from, but its kinda the same principle. Make sure the LED is running on 5V though.
Actually looking now, the digital read tutorial doesn't do a digitalwrite, it uses an external 10K resistor. Thatd work too though requires you to have another part in your system.
Note crosscheck this with someone else before going and trying it. I'm still a scrub with electronics.