Like thermostats that learn your heating and cooling patterns, these new Stack light bulbs are billed as the first “responsive” light bulb. The company offers a number of benefits for the Stack light system, including better sleep, hands free operation and energy savings.
Circadian Lighting—The Stack light bulb can adjust the color temperature (warm/yellow or cool/blue) to the time of day, which can help your body regain more natural circadian rhythms offering more natural sleep patterns and better alertness during the day.
Occupancy Sensing— If you loved the motion sensing lights often found in European settings, this is an attractive feature. Stack senses when there are room occupants to turn the lights on and off automatically. The website notes that “you’ll never have to flip a switch again.” This could be a boon to those family 
members who are continually turning off lights throughout the house.
Light Sensing— Here’s where the energy savings can really kick in: Stack lights automatically dim and brighten according to the natural light in the room, and as a result can reduce energy consumption by as much as 40-60%.
Like many of these new smart home devices, Stack is easy to set up. Just plug in the Stack hub, screw the bulbs into existing fixtures and set up your Stack using a smartphone app. According to the manufacturers, the light will learn your preferences over time, becoming effortless in lighting based on your preferences. A Stack starter kit —reasonably priced at
$89-$99—comes with two Stack lights and a wireless hub. Additional bulbs are $28 for a classic style bulb and $45 for a “down” light.