I doubt that complete darkness is necessary. In my opinion, we have evolved with a certain exposure of natural light (moon, fire etc.) while still being able to maintain a good sleep.

I believe that we need to remove all artifical light during night (and maybe also during day) that could interrupt our natural cycling between night and day.

Also, when you want to wake up, there should be a natural environment of a rising sun or increased natural lighting to trigger the start of the day. This is why I think that waking up in complete darkness is not necessarily healthy.

My 2 cents

I use an eye mask. Works great!

I have huge pieces of cardboard that I fit into the window frame. Then I roll down the blind, put a towel across the windowsill, and draw the curtains. This keeps out most of the light from the window.

I put a towel on the floor against the bedroom door, too, because light coming under the door is enough to wake me.

Crazy, isn't it? But I sleep way better since I've started doing this.

I live 40 minutes from the nearest town at the end of a dirt road :)

From what I read, you need darkness on the blue side of the spectrum, any little bit that hits your skin is enough to register and screw up your sleep. (Of course, less is always better than more even if you can't get to none.) If it's low intensity light sneaking through your blinds, that's probably ok, street lights and the like are generall Sodium Ion lamps and run on the yellow-red side of the spectrum. It's the fluorescent type lights that run blue that you have to worry about. Also watch the LEDs in the bedroom (i.e. the smoke alarm), they're much more intense than you think.

I live downtown in a big city... needless to say it's a lot brighter outside my window then natural full-moon lighting. But I am lazy so if it's bothering me I drop the AC and pull a tobagon/ski-cap over my eyes. Works perfectly. Goes just to the tip of my nose and no light gets in unless I open my eyes and look towards my nose. Also it's pretty cozy.

I don't sleep in total darkness and I sleep great. In fact, I don't see how you could wake up normally if there's no light to cue you.

Hayley and I have been sleeping in a pitch black room for about 6 weeks now, and the sleep difference is TREMENDOUS. She claims that her dreams are far more vivid, and we both feel better rested and more energetic the next day.

Here is our pre-bed checklist of things to keep the room pitch black:

• Blankets over the window. (we use thumbtacks and tack up heavy, doubled up blankets over the windows so that the blanket extends about 6" beyond the edge of the window)-
• Electronics off or covered up. (We will throw small towels over all electronic items that emit any light. This even includes the charge ports for our cell phones, the macbook, the light at the end of power strips, the wifi router, and alarm clocks)

Other than that, there really isn't much else to do. We keep about 6 hand towels in the bedroom to cover electronics while we're sleeping. The difference in our sleep quality is night and day [rimshot please!]

Hope this helps!

In Portugal, where I live, every house has roller shutters - that pretty much blocks all light coming from the window.

Other than that, I've covered all the artificial light sources in the bedroom (DVR clock, TV standby light, etc).

The fog horns under the Golden Gate Bridge have the same frequency as mammoth bellows and as a result I sleep soundly. Goodnight.