In this post we learn how to make a sunrise/sunset simulator circuit using LEDs and just a couple of BJTs. The idea was requested by Mr. Jerry
The Circuit Request
Apparently natural daylight is best for humans in regulating our circadian rhythm. I would like to build an LED lighting circuit to control ceiling LED lamps for my darker and windowless rooms. I'm hoping for thin flat panel lamps with a nice trim could mimic the characteristics of natural daylight (as coming through a window).
I envision a solar panel outside regulating our circuit and possibly charging a back-up battery.
To create the change of kelvin and brightness that natural daylight has during a typical day, we may be required to use a soft-white and a bright-white LED combo to create about 1100 lumin from each lamp. Kelvins and brightness start low in the morning and increase towards midday then fall off as evening approaches.
None of the companies I've seen do this any of this well imo. Some don’t have a kelvin adjustment. Other companies went Wi-FI smart bulb route, but they have timing circuits that get out of sync with the seasons and other issues.
I'd like to make thin flat panel lamps with nice molding trim and maybe have 2 lamps per circuit. Making it to handle 1 to 4 lamps would be an ideal option, but more issues in the circuit build. Using a small solar panel outside and a battery/ charge circuit indoors for night time lamp use and power outage lighting.
I appreciate any thoughts. Making just a single one lamp circuit and using simple power supply for night time use would be a great start to make lighting work this winter
The Circuit Design
As proposed, a simple sunrise and sunset simulator circuit can be implemented using the circuit shown in the following diagram:
The entire circuit can be seen powered from a single solar panel for the required sunrise/sunset simulation effect on the connected LEDs.
The NPN BJT stage using the TIP122 becomes the main section of the circuit and can be expected to execute the required slow brightening of the yellow/white LEDs proportionately in response to the rising sunlight level exposed on the solar panel.
The PNP stage using TIP127 is optional and this stage is introduced to do the exact opposite of its NPN counterpart. The indicated cool white/blue LEDs are supposed to gradually illuminate and get brighter as the sunsets.
During day time, the solar panel operates the gradual brightening of the warm LEDs simulating sunrise effect, and simultaneously it also charges an attached back up battery.
When night falls, the same battery provides power to the cool white LEDs which keeps the house illuminated when its completely dark.
The battery is also under-charge protected since the 4 LEDs which are connected in series simply stop conducting as soon as the battery voltage drops below the 11V mark making sure that it does not go through a deep discharge.
For the above shown example sunrise/sunset simulator circuit using LEDs, the approximate specifications of the components could be selected as described below:
Solar Panel: 18V, 1 amp
LEDs: 3.3V 1 watt