Solar Spectrum LED Tower

January 8, 2022


This project was an attempt to recreate the appearance of sunrise morning light with some LEDs. Early morning sunlight coming in through the window seems to have a mysterious energy to it, giving a subtle rich coloration to the room which somehow is not easily matched by regular lighting solutions, with the latter appearing relatively dull. Would it be possible to get a similar coloration with an artificial light source?

There are two factors to consider: the spectrum of sunlight vs skylight, and also the directionality or diffuseness of sunlight vs skylight. The sun near the horizon has a yellowish look with a lower color temperature, while skylight is a bluer, dimmer, and more diffuse light. The more diffuse skylight also produces more diffuse shadows compared to direct sunlight. The combination of yellow and blue, both on object surfaces and in object shadows, with the low angle of incoming sunlight casting long shadows, gives the rich coloration and contrast compared to normal overhead lighting.

Here I used LEDs designed to recreate a large portion of the solar spectrum (including importantly the red end, which is often poorly covered in cheaper approaches), purchased from The sunlight is simulated by a 2700 K color temperature LED strip ("Centric Home"), while skylight is simulated by 6500 K color temperature LED modules ("Absolute Series"). Both are attached around a metal tube which acts as a heatsink, and connected to a dimmer.

Photo of the assembled prototype LED tower. The lower section has yellowish 2700 K LEDs, while the upper section has bluish 6500 K LEDs.


A photo of a box label taken with overhead fluorescent lighting (left), and with the solar spectrum LED tower (right). With the tower, the red colors are slightly richer, shadows and glares are more prominent. It should be noted this is really not a good color test sample (it's the best I could find at the time), since the inks themselves have a limited spectral response and the colors on the label are based on linear combinations of ink dot size. The advantage of the full spectrum LEDs will be more evident with richer natural materials.

This combination of LEDs generated a pleasing appearance in the room, with objects in shadows having some different blue and yellow coloration due to the different vertical locations of the LEDs on the tower. The tower itself is at eye level which gives shadows similar to those of sunlight coming in through the window. Looking away from the tower, there is a satisfactory emulation of the "morning sunlight" invigorating effect, even though the diffuseness of the LEDs is not properly matched to what would actually be seen in the sky. However, an issue arises when looking in the direction of the tower, because the bright LEDs end up shining into the eye and it is unpleasant to have the operating LEDs in the field of view. Overall, this implementation is not something I would want to use as a regular light source, but it does prove that with proper spectrum matching one can simulate morning sunlight. In an improved version I would recommend finding some way to distribute the blue light over a wider area, while concentrating the yellow light into a narrower angle, so that one can look in the direction of the tower without disturbance.