Part of the interest in this project revolved around building and testing tools we've always dreamt of having access to over a lifetime of obsessing over artificial lighting. Some of the fun we had involved color temperature measurements with sources outside of the commodity lamps selected for this prototype. This included, unbelievably enough, traditional filament incandescent lamps and halogen capsule lamps also rated for the same 800 lumens range as those selected for the prototype.

One feature which was immediately visible in the Color Temperature vs. Power testing was the natural tendency of incandescent lights to shift their color temperature as they are dimmed. I've zoomed into the range previously examined for our LED sources to highlight that range here for a standard 60 watt incandescent and 60-watt equivalent halogen (the latter being commonly available today as an energy-efficient incandescent replacement option).

Testing of color temperature readings relative to power levels for older filament incandescent and halogen capsule lamps.

Note how unlike the LED lamps in the prior log, these lamps have a graph best expressed as a polynomial and represent shifts of approximately 10-20% in color temperature. This noteworthy distinction is significant in that it is a natural function of the method by which incandescent lamps operate, but not of the sources which have replaced them. This has led to manufacturers attempting to emulate this functionality on newer sources using various techniques... the availability of which convinced this team that the project we have proposed might even be possible!

One problem we noticed in calculating color temperature values for these lamps was that the resulting number seemed far too low relative to expected values. This problem may likely be a function of skipping the calibration step and is likely exacerbated by the differences in spectrum between the LED sources and the incandescent sources (see our earlier entries comparing the normalized spectra of incandescent and fluorescent sources as well as the spectrum of LED sources).

For anyone worried about our lighting bills, please rest assured that these lamps were returned back to their safe resting places in the "lamp and bulb curiosities" box and aren't being kept in regular service.

A newer capsule halogen lamp on the left and an old filament incandescent lamp on the right. To produce a comparable amount of light (800 lumens) the incandescent consumes 60 watts (and doesn't really output a full 800 lumens) while the halogen does so with just over 50 watts... while all the LED sources used in the prototype do so with under 9 watts(!)