One of the stated goals of the project is to create a color temperature controlled light source using commodity LED lamps. With such a wide range of possibilities available in the market today two primary constraints were used to guide the team on lamp selection:
- Select for dimmable LED lamps of a type widely available at retail.
- Select lamps of multiple color temperatures to facilitate color control.
Fortunately dimmable LED lamps are indeed available from every imaginable retailer. For this project we opted to source our LED lamps from big-box home improvement stores primarily due to the wide selection available in that setting.
Selecting lamp color temperature deserves a modicum of explanation as the sources in question (at this stage) are all still fundamentally white light sources. Retail buyers will be familiar with correlated color temperature (CCT) labels on lamps by either their numerical value, expressed in degrees Kelvin and typically in a range between 2000 K and 6500 K, or by their marketing terms such as warm white (temperatures in the 2000 K range) , soft white (often used for temperatures in the 3000 K range) to cool white and daylight (referencing temperatures from 5000 K and above). Future project entries can elaborate upon the some of the meaning behind these terms.
Nonetheless, even with the constraints above the options available remained numerous so a few other considerations were selected as options which might facilitate early testing. Note that these are choices which could later be intentionally ignored as we learn more about the capacity of the system to provide a color-controlled lighting experience and also as we consider opportunities for expanded functionality from the device.
- Select for lamps of comparable lighting output (lumens).
- Select for lamps with a comparable light source structure.
The first choice meant that in theory the system would, at a minimum, allow direct switching between two or more color temperatures at an equivalent level of output. This functionality is typically limited to smart lighting or special purpose lamps/fixtures. Another functionality this should automatically enable would be a dim-to-warm experience where lower lighting levels could be tied to lower CCT values, emulating the dimming performance of older incandescent lamps. Again, this is a feature that is sometimes integrated into premium, manufacturer-specific LED lamps but is otherwise not a normal functionality associated with LED dimming.
The second choice is more complicated but was also a consideration as part of the testing phase. LED light sources are highly directional and, as such, LED lamps use all manner of methods to position LEDs and route their light output to ensure appropriate distribution of light. Typically, LED lamps designed as incandescent-replacements attempt to match the pattern of light distribution appropriate to the lamp shape (omni-directional for classic A-lamps, to highly directional for reflectors). To prevent differences between models from creating measurable differences with the testing platform one additional refinement was made to initially opt for LED filament-style lamps of comparable shape. This should hopefully minimize any differences at the sensors which might occur because of significant differences in beam shape and LED placement (though other considerations will also be made regarding sensor placement to further minimize this issue).
Given all of this, the following two lamps were selected as the primary range of light sources for our initial testing:
|Soft White (2700 K)||Daylight (5000 K)|
These lamps are relatively inexpensive if not cheap by today's standards at under $6 per individual lamp. The shape is a straight tubular design popular for vintage/retro- applications known as ST19. Note how both lamps have their LED filaments oriented in the same vertical fashion. The lamps are both rated to output 800 lumens which, though referenced as a 75 watt replacement for vintage ST19 lamps, puts them at exactly the output considered a 60 watt incandescent equivalent when discussing typical Arbitrary shape lamps (A-shape) such as the one pictured in our project banner. I'd also add that both lamps are rated at 90 CRI, which is a color rendering index. This metric is complex and worth another future project entry, but suffice it to say that these lamps should perform well at rendering colors in their associated color temperature range.
In an effort to further expand the potential range of color temperatures two additional lamps were selected at the extremes of what is available in the market:
|Amber (2000 K)||Daylight (6500 K)|
The first example is a directly comparable ST19 lamp rated at 2000 K. This lamp is comparable to the earlier choices, having a similar lumens rating, shape, and construction. The only noteworthy distinction is a lower 80 CRI (which is specific to the lamp and not necessarily relate to the lower color temperature). Note that 80 CRI is a common CRI rating for mass-market LED light sources. The 6500 K daylight lamps are a different lamp shape but close examination shows that they have a similar (if more compact) vertical LED filament positioning. Note that the cool daylight lamps are of as yet undetermined CRI, though the lack of an Energy Star rating suggests that these are likely in the typical 80 CRI range (current Energy Star ratings mandate a minimum 90+ CRI for omnidirectional lamps, explaining why so many manufacturers attempt to position replacement lamps with that rating).
Note that all the lamps above sip a mere 8.5 watts to generate their 800 lumens (compared with 50-60 watts in an incandescent source), meaning that at their maximum they are rated to output over 94 lumens per watt. One of the more interesting pieces of data which may come out of this experiment will be a measurement of efficiency changes relative to output.
Take note that an explicit effort was made to reference these devices by their industry name, lamps, rather than bulbs. As lamps these are by definition replaceable and self-contained sources in contrast to the term bulb which is typically taken to reference the glass, filament-containing end of a typical incandescent lamp. As a core purpose of this project is to create a flexible solution which could leverage devices of different types and capabilities, identifying the sources as lamps was a critical part of communicating the modular nature of this solution.