Blue light and sleep deprivation
Studies have shown that artificial light in the evenings and at night suppresses our melatonin production which disrupts circadian rhythms while asleep. The biggest disruption comes from "blue" light and other lights higher up on the visual spectrum such as those emitted by modern televisions and smart phones. The lowest disruption comes from red lights at the bottom of the visual spectrum.
I was recently advised to switch to red lights in the evening to help with my sleep patterns. I am told that the key is to achieve light as low as possible on the spectrum. Can this be achieved by filtering a white light through a red cover or does the light emitted have to be intrinsically red itself (eg the difference between a Christmas light with a red cover and a red heat night light for reptiles)?
If my smart phone is "blue" light even when it displays many different colours then can a standard light bulb with a red filter also still be considered "blue" or "white" light and therefore in the higher melatonin-suppressing end of the spectrum?
My doctor told me the same thing about blue light and sleep patterns. I have learned the hard way that I can't use my computer within an hour of bedtime and expect to go to sleep. At night, humans traditionally had only firelight, which is red, with maybe a bit of star/moonlight. Therefore, your brain thinks blue light means daytime.
The easiest thing to do is replace all your compact fluorescent bulbs or LED bulbs with non-halogen incandescents. Compact fluorescent and LED bulbs put out a lot of blue and green light in addition to red--see a compact fluorescent spectrum at http://protonsforbreakfast.wordpress.com/tag/spectra/ (scroll down a bit). Incandescent light is almost all red (see the spectrum on the same page). You don't perceive it as red because your brain adjusts its "white point" so that most things look the same color no matter how they're lit. However, if you've ever thought your face had a greenish cast in the office, it's because of the green emission from fluorescent lights.
You could filter white light through a red filter, as you suggested. Such a filter would absorb blue and green light so it wouldn't reach your eyes. As far as your brain is concerned, it doesn't matter if the light source is intrinsically red or filtered. But it would be tricky to find red filters for all of your lights. Incandescent bulbs are much easier, though not so great for the environment. Red-tinted lamp shades could also work.
Your smart phone is tougher. Even though it doesn't look blue (because of the way your eye adjusts its white point), it has an LED (light-emitting diode) display. See the LED smartphone spectrum at http://www.displaymate.com/Spectra_4.html and note the fraction of the total light that is blue---WAY more than for an incandescent light, even more than for the Sun. Your smartphone doesn't give off as much light as the Sun, but the light it gives off is bluer than daylight. The only thing to do is to put away the smart phone in the evening.
Edited to add: I just learned about the Twilight app that adjusts the color scheme of your phone based on the time of day. In the evening, it shifts toward redder colors. Twilight is available for Android OS. (This is not a product endorsement.)