Electronics Weekly covered the effect of LED light circadian (sleep-wake) rhythms - scroll down to 'Sleep' here.
There are a whole bunch of inter-related light effects in the eye/brain that can upset sleep and, very roughly, the more blue you are exposed to before sleep, the harder it can be to get to sleep - and LED lighting is largely based on blue LED die. Melatonin is the key hormone affected.
“My daughter was having trouble falling asleep at night,” said Saffron CEO Preston Wily. “She wanted to read. I wanted her to sleep. I came up with the idea of a bulb that slowly dims itself until it eventually turned off allowing her to read for about a half an hour before the light turned off. The prototype had an unexpected result: she fell asleep faster than she would when I just turned her lights off. I knew we were on to something.”
What he came up with is a bulb that automatically dims over 37 minutes - it also works like a normal bulb, and does some other stuff (see below).
Knowing what we know about blue light and sleep, we asked Wily a couple of questions about negotiating circadian complexities, which revealed he is taking the subject seriously:
When your bulb mimics the setting sun, how does the blue content of the light behave?
"Our first prototype adjusted the colour temperature as it dimmed, but after consulting with light therapy research we learned that you should avoid any exposure to blue light within 2-3 hours of bed time. Since the Drift Light was meant to run through its entire dimming program in less than an hour we decided to just use a warm [2,700K] colour temperature," said Wily.
Does it really go, or are there still blue die active in the bulb, even if they are behind phosphors?
"By changing the colour temperature we were able to significantly reduce the blue light emitted, but you are correct that we did not completely eliminate the presence of waves in the blue spectrum. When we completely filter these out the light takes on a reddish tint that most people didn't like. We are experimenting with different alternatives, though, and are considering another product geared toward people who want to completely eliminate it."
UK lighting firm PhotonStar has also taken the subject seriously - you can read about its ChromaWhite II product here, which can completely cut its blue output.
Back to Drift Light
Saffron's Drift Light has three settings, via an internal microcontroller:
Daylight Mode - like a normal light bulb, illuminated at full power - 530 lm.
Midnight Mode slowly dims the bulb until it is completely off.
Moonlight Mode slowly dims the bulb until it is at night-light brightness.
The last one is for children who are either afraid of the dark or who like to sleep with some light on, and also for hall ways.
To initiate Midnight Mode, the light switch is flipped twice, or three times for Moonlight Mode
Switch dimming is a nice idea that retains standard wiring and needs no wireless interfaces or smartphone intervention - and means off really means off, adn not just an nominal 'off' that is actually power-consuming active stand-by. EnOcean's wireless interfaces used to consume over 1W when 'off'. I wonder if they have cut that yet?
Supertex (now owned by Microchip) makes chips for LED lighting with switch dimming - one example is the HV9801A which cycles through 100, 50, 25 and 12.5% intensities when the light switch is clicked.
One other thoughtful thing about Drift Light is, "it features a diffusing cap made of plastic, which makes it almost impervious to drops or bumps", said Saffron.