Anders Hoveland
Enlightened
- Joined
- Sep 1, 2012
- Messages
- 858
An LED emitter generally emits just one distinct color wavelength. The type of white color LED that has become ubiquitous involves using a blue wavelength LED emitter with phosphor, to convert some of the blue light into other wavelengths.
What I would like to discuss here is something we often do not consider. Phosphor-converted white LEDs may use different wavelengths of blue emitters, depending on the design.
Many white LEDs use a 465nm emitter.
I have some cheap Chinese "sky blue" color LEDs that seem to be using a 470-475nm emitter with some green phosphor.
The Cree LS (using TrueWhite technology) uses a 440nm blue emitter.
I have a Philips Luxeon lime color LED (highly efficient, 190 lumens when run at 1W) which uses a 430nm emitter with greenish-yellow phosphor.
(only a very small amount of 430nm gets through)
Of course, underdriving a blue LED emitter can shift the wavelength a little. When run at 30% of its rated power, the wavelength will typically increase by about +3nm.
These different emitter wavelengths have an effect on the quality of light emitted. The color shift resulting from even a 3 nanometer shift in blue wavelength can be noticeable to the human eye. That is why manufacturers are often concerned about color shift in dimmable white LED products.
(the human eye is much more sensitive to wavelength changes in this blue-green region of the spectrum than it is in other parts of the color spectrum)
Then there is color rendering. Shorter wavelengths of blue typically render blue colors more of a pure vibrant indigo blue, whereas much longer blue wavelengths can render blue colors more faded, or sometimes even a little greenish-blue. There is a clear difference in how jeans look under a white LED using a 465nm emitter compared to 470-475nm.
The third effect has to do with perceived harshness. I have never seen anything written about this effect, but my personal observations suggest that shorter blue wavelengths seem to be "harsher" on my eyes, more difficult to concentrate on. Using a multi-emitter LED array to generate white light for reading, it seems much easier on the eyes when using longer wavelengths for the blue, and I experimented with several different wavelengths.
This range of "blue" wavelength emitters can really span from azure blue to indigo, even violet. There are advantages and disadvantages to using different blue emitters.
What I would like to discuss here is something we often do not consider. Phosphor-converted white LEDs may use different wavelengths of blue emitters, depending on the design.
Many white LEDs use a 465nm emitter.
I have some cheap Chinese "sky blue" color LEDs that seem to be using a 470-475nm emitter with some green phosphor.
The Cree LS (using TrueWhite technology) uses a 440nm blue emitter.
I have a Philips Luxeon lime color LED (highly efficient, 190 lumens when run at 1W) which uses a 430nm emitter with greenish-yellow phosphor.
(only a very small amount of 430nm gets through)
Of course, underdriving a blue LED emitter can shift the wavelength a little. When run at 30% of its rated power, the wavelength will typically increase by about +3nm.
These different emitter wavelengths have an effect on the quality of light emitted. The color shift resulting from even a 3 nanometer shift in blue wavelength can be noticeable to the human eye. That is why manufacturers are often concerned about color shift in dimmable white LED products.
(the human eye is much more sensitive to wavelength changes in this blue-green region of the spectrum than it is in other parts of the color spectrum)
Then there is color rendering. Shorter wavelengths of blue typically render blue colors more of a pure vibrant indigo blue, whereas much longer blue wavelengths can render blue colors more faded, or sometimes even a little greenish-blue. There is a clear difference in how jeans look under a white LED using a 465nm emitter compared to 470-475nm.
The third effect has to do with perceived harshness. I have never seen anything written about this effect, but my personal observations suggest that shorter blue wavelengths seem to be "harsher" on my eyes, more difficult to concentrate on. Using a multi-emitter LED array to generate white light for reading, it seems much easier on the eyes when using longer wavelengths for the blue, and I experimented with several different wavelengths.
This range of "blue" wavelength emitters can really span from azure blue to indigo, even violet. There are advantages and disadvantages to using different blue emitters.