Rods and Cones and ???????...
In less than one generation, several new technologies that are capable of resetting our circadian cycle and disrupting our sleep patterns have become ubiquitous. For some reason, while pharmaceutical companies are making huge profits selling hypnotic sleep drugs, people are not being told about what may be causing the impairment of their sleep.
Around the turn of the century, it was discovered that there is a third kind of photoreceptor, in addition to rods and cones, in our eyes! This receptor is optical but not visual: it does not contribute to vision, and it can function in people who cannot see.
One apparent function of this receptor is to use daylight to maintain the setting of our biological clocks. Here's basically how it seems to work:
When the Sun is very low in the sky, at sunrise and sunset, its light is rather yellowish, almost reddish. But that effect is a continuum; it is least yellowish at noon when the sun is directly overhead. The 3rd photoreceptor is sensitive to that most whitish/blueish light. Certain blueish wavelengths at high intensity tell our bodies that it is mid-day.
Melatonin is a brain chemical that is necessary to sleep. When the 3rd photoreceptor tells the brain that it is mid-day, the brain produces less (or suppresses production of) melatonin. That is how our sleep cycle is regulated, and can be disrupted...
Within the past 20 years, new lighting and display technologies have appeared that can, as far as the 3rd photoreceptor is concerned, mimic mid-day light, and thus suppress our melatonin levels, and thus disrupt our sleep.
Blue LEDs (Light Emitting Diodes)
For decades, LEDS have found their way into the devices that have found their way into our lives. The first LEDs were red. Eventually they showed up in orange, yellow, and green. There were also blue LEDs, but for a long time they were far more expensive to produce. Suddenly, in the late 20th century, blue LEDs became affordable, and manufacturers embraced their use. Their light became fashionable; in part because it had a unique appearance and it signified a new device. Apparently their use resulted in increased sales; manufacturers engaged in blue-wars, trying to out-blue each other.
But exposure to such light can be sufficiently bright to trigger our 3rd photoreceptor, which our brains interpret as a need to suppress melatonin production. And that delays the desire to sleep and makes a good night's sleep more difficult to obtain.
LCDs (Liquid Crystal Displays)
Most modern (laptop) computer displays and HDTVs are flat-screen LCDs. They utilize some kind of backlighting to provide a broad-spectrum white light, and then individual pixels can block some or all (colors) of the light shining through that pixel from behind. Many portable devices, including GPS and smart phones, also use LCDs for their displays.
On the showroom floor, extreme brightness seems to be a sales/survival advantage. In manufacturers' zeal to provide the brightest display for the money, the ability to accurately display images with a low backlight level has been sacrificed in many displays.
Many LCDs have a good deal of light that, in addition to what shines through the white portions of the display area, leaks out around the edges even when all the pixels are black. This light is whiter (and thus better able to reset your circadian clock) than what has more traditionally been emitted by bulky old glass CRTs (Cathode Ray Tubes).
HID (High Intensity Discharge) Headlights
Cars and trucks now often come with HID headlamps. These bright blueish-whitish lights are far less yellow than more traditional halogen incandescent headlamps. While responsible vehicle manufacturers do tend to show a little restraint in this regard, some people are suckers for numbers, and foolishly change their lights for aftermarket replacements that have the highest color temperature they can find on the internet...
So if you find that your sleep is not as good as it used to be, it may be because your melatonin levels are being suppressed by exposure after dark to these modern sources of blue-ish light.
Adjusting Your Melatonin Level
You can test that possibility by avoiding such sources of artificial lights after dark. For example, don't bring that cell phone with the bright blue backlit keys up to your face. If that is not possible, there are melatonin supplements available at some drug and health food stores.
In our experience with melatonin supplements (pills), any melatonin product will help you get to sleep (assuming your sleep impairment was caused by a low melatonin level), but only time release melatonin will help you stay asleep, and also help you get back to sleep if something awakens you during the night.
As when experimenting with any drug that is new to you, it is a good idea to start with an extremely small dose (1 mg is more than enough for a first try; don't be afraid to split a pill) and then, if the desired results were not achieved, try slightly more the next night...
Why pay a pharmaceutical company for a powerful hypnotic drug when simply adjusting the level of a naturally-occurring brain chemical can more directly compensate for a common cause of 21st-century sleep disruption?