This week, the lighting start-up company vu1 is beginning to ship a new type of lightbulb that could displace compact fluorescents and LED lamps as the energy-saving bulb of choice.
The technology, known as cathodoluminescence or electron-stimulated luminescence (ESL), offers similar energy savings, but provides a more natural quality of light.
My life in the past several years has been a living lightbulb joke. I’ve changed, re-changed and re-re-changed the bulbs in my house trying to find replacements that save money but don’t make our skin look like zombie flesh. Compact fluorescents and LED lamps save energy, last longer, and emit less heat than incandescent bulbs. But their light is ickier, versions advertised as “dimmable” often dim only over a limited range, and CFLs take maddeningly long to come to full brightness. No single type works everywhere. LEDs are great for desk lamps, but their narrow beams fail to fill larger spaces. In darkly painted rooms, I went with cold-cathode fluorescents with alow brightness temperature. I’ve filled a big box in the basement with all the bulbs I’ve tried and rejected. So much for saving money.
The color quality has to do with how these bulbs work. The white(ish) light you see is given off by a phosphor coating. In a CFL, the phosphor glows when backlit by ultraviolet light from mercury vapor; in an LED bulb, it soaks up light from a pure-blue LED. (The mercury is why you can’t just throw a CFL in the trash when it dies.) On the left is a graph showing the spectra of incandescent, CFL, and LED bulbs; the x-axis is the wavelength in nanometers. Although this particular graph was provided to me by vu1, which has a certain self-interest in showing its competitors in their worst light, it matches information from other sources such as the lighting control company Lutron and the RPI Lighting Research Center. The CFL spectrum is a series of spikes, reflecting the combination of phosphors used to approximate white light; CFLs therefore accent certain colors and fail to render others.
LED bulbs, which use a different type of phosphor, have a smoother spectrum, but the blue LED that drives the phosphor creates a sharp peak in the blue, short-wavelength range of the spectrum, which might pose a “blue light hazard.” Ignacio Provencio of the University of Virginia will have an article in our May issue about how our eyes have a special class of photoreceptor that doesn’t form images; instead it absorbs blue light to synchronize our body clock with the day/night cycle. Too much blue light coulddisrupt your sleep cycle. I’ve also seen claims that excessive blue light might fry your retina and increase your chances of developing macular degeneration. The French counterpart to OSHA issued a report last November warning that children are at particular risk, although Physics World quoted other experts who thought the claims overblown.