Tuesday, May 12, 2015

LED color temperature

A new contact that works on lighting castles sent me the photo below. It compares the light provided by an incandescent lamp (left) to the "warmest" white LED that their group could find (right).

Image used with the permission of the
Prussian Palaces and Gardens Foundation Berlin-Brandenburg

The problem with the LEDs, from her perspective, is that the blue light component is too large, and the colors of the objects in the castles are not properly represented. LEDs can be adjusted to provide nearly any color that's desired, but their "luminous efficiency" is often worse than a very cold, blue-white LED. This is the main reason why so many LED street lights glare with such an ugly, cold light. But it doesn't have to be this way!

An overly narrow focus on the luminous efficiency of lamps misses the point about saving energy. For example, regardless of how high the luminous efficiency of the lamp in this photo is, it's not being used in an efficient and sustainable way:

Light on during the day by Christopher Kyba is licensed under
a Creative Commons Attribution 4.0 International License.
Some colleagues and I wrote an article about how a more common sense view of the "efficiency" of a lamp its energy use per year, not the efficiency with which it converts electricity into light causes a human visual response.

While making a decision about how to light a space, energy consumption is a very important consideration, but the people who will use the light should never be taken out of the equation! In Davis, California, the city decided to let citizens choose which lamps they liked after residents  had protested the installation 4,000 K LED streetlights. The public ended up choosing warmer 2,700 K lamps. In addition to being more liked (or at least more tolerated), warmer LED lamps also have a smaller impact on the night sky than the most efficient white LEDs.

When the Nobel prize was announced last year, I wrote:
"It's possible to imagine a future in which driverless cars run without headlamps ... pedestrian and cyclist lights provide more uniform lighting at greatly reduced light levels, and the sky above even large cities once again glitters with thousands of stars."
For that to come to pass, the focus of sustainable lighting is going to have to shift beyond luminous efficiency, and keep the users of light in the center of focus.

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