Lamp Output vs. Power

A project log for Lighting Color Control with Commodity Lamps

A controller system using consumer LED lamps to provide color temperature control and management alongside daylight dimming.

JonJon 09/24/2020 at 08:150 Comments

The first results that were collected from the system were the normalized responses of the lamp light output relative to the power input. Rather than list the measured power level I've simply used the abstracted power levels used by the lighting controller board (a range from off at 66 to full on at 0). Although it was possible to calculate the measured lumens of each lamp once an exact distance between the lamp source and the sensor was measured, the method used to produce this graph involved using the rated lumens rating of the lamp as a reference relative to the readings measured by the ambient light sensor.

A graph of the output (lumens) of each lamp versus the power level setting in the lighting controller.

Right away there are a couple of curves that stand out for cutting across the others: that of the GE Cool Daylight and the Feit Amber lamp. I've included a halogen incandescent and Cree Exceptional Light Quality LED lamp in this stage as controls to provide some reference lines for what are otherwise lamps selected as commodities and not because they are highly rated for their compatibility with dimmer circuits (as is the case with the Cree).  Some manipulation of the data by changing the scale to logarithmic and reversing the order of the data amplifies what is happening.

The same data with the vertical scale made logarithmic and both vertical and horizontal scales inverted.

The halogen lamp reaches the highest point in this version of the graph, demonstrating that it has the widest range of lighting levels. However, this may not be entirely useful since there may be little to no value gained from being able to control light output at such low levels as single-digit lumens. In contrast, the Feit Amber has the lowest starting point on the graph indicating a short range from minimum to maximum brightness.

The Cree and EcoSmart lamps have the widest graphs demonstrating that they make maximum use of the power output range of the dimming circuit relative to their supported brightness ranges. The narrower graphs of the GE and Feit lamps suggests that they would provide less granular dimming control relative to the other lamps.

Of course, a big factor to consider here is the design of the dimming circuit. Though certainly worthy of a dedicated post, suffice it to say that the power control method used by this particular controller - known as leading edge dimming - is actually not of the type best suited to controlling LED lamps - that would be trailing edge dimming. As such, a circuit more optimized for controlling LED lamps might demonstrate wider control ranges for the Feit or GE lamps, and taller output light ranges for sources like the Cree.

Ultimately the EcoSmart lamps have to be congratulated for performing very comparably to the highly-rated Cree in this particular measure. The GE lamp performance is somewhat disappointing given the prominence of the GE lighting brand, whereas the limited range of the Feit Amber shouldn't be too surprising or discouraging for what is very much a specialty lamp likely not intended for general illumination.

As one of the target applications of this control system, we've already used this collected data to create what could be termed the ultimate dim to warm lighting range. Dim to warm LEDs like the Warm Glow series from Philips lower the output color temperature as the light is dimmed to simulate a similar result which occurs with incandescent lamp dimming. However, this color temperature shift is usually small, moving a 2700K lamp to 2200K when dimmed.

Using the dimming data above and the full spectrum of the lamps targeted for this prototype it was possible to create a scenario where the lamp output at full brightness possessed a cool 6500K temperature and, while dimmed, took the lighting color temperature down the very warm (and perceptibly red) 2000K temperature of the Feit Amber lamp before finally shutting off. This can be challenging to properly capture in video as it requires controlling for aperture and white balance, but the image below gives some insight into what is immediately possible with the controller circuitry at this early stage. More to come regarding color spectrum and color temperature measurements!

A dim to warm range from 6500K at maximum illumination - 800 lumens - down to 2000K at 200 lumens and below. Note the color shifting on the white door and colorful board game boxes (despite the camera attempting to accommodate the changing light levels and white balance).