To be more energy efficient, many people have replaced their incandescent lights with LED bulbs. However, those currently on the market emit a lot of blue light, which has been linked to eye troubles and sleep disturbances.
Now, U.S. National Science Foundation-funded researchers reporting in ACS Applied Materials & Interfaces have developed a prototype LED that reduces -- instead of masks -- the blue component, while making colors appear just as they do in natural sunlight.
LED lightbulbs are popular because of their low energy consumption, long lifespan and ability to turn on and off quickly. Inside the bulb, an LED chip converts electrical current into high-energy light, including invisible ultraviolet, violet or blue wavelengths. A cap that is placed on the chip contains multiple phosphors -- solid luminescent compounds that convert high-energy light into lower-energy visible wavelengths.
Each phosphor emits a different color, and these colors combine to produce a broad-spectrum white light. Commercial LED bulbs use blue LEDs and yellow-emitting phosphors, which appear as a cold, bright white light similar to daylight. Continual exposure to these blue-tinted lights has been linked to cataract formation and turning them on in the evening can disrupt the production of sleep-inducing hormones, such as melatonin, triggering insomnia and fatigue.
To create a warmer white LED bulb for nighttime use, previous researchers added red-emitting phosphors, but that only masked the blue hue without getting rid of it. So, Jakoah Brgoch and Shruti Hariyani at the University of Houston wanted to develop a phosphor that, when used in a violet LED device, would result in a warm white light while avoiding the problematic wavelength range.
As a proof of concept, the researchers identified and synthesized a new luminescent crystalline phosphor containing europium. In thermal stability tests, the phosphor's emission color was consistent between room temperature and the higher operating temperature, 301 degrees Fahrenheit, of commercial LED-based lighting.
In long-term moisture experiments, the compound showed no change in the color or intensity of light produced. To see how the material might work in a lightbulb, the researchers fabricated a prototype device with a violet-light LED covered by a silicone cap containing their luminescent blue compound blended with red-emitting and green-emitting phosphors. It produced the desired bright warm white light while minimizing the intensity across blue wavelengths, unlike commercial LED lightbulbs.
The prototype's optical properties revealed the color of objects almost as well as natural sunlight, fulfilling the needs of indoor lighting, the researchers say, though they add that more work needs to be done before it is ready for everyday use.
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I feel for you. Been there done that. I design LED grow lights for Horticulture Research at the University of Florida.
LEDs are so much more complex than one would think. So much so I am currently writing a paper titled "Understanding LEDs"
There are blue LEDs and there are Royal Blue LEDs.
Blue is typically around 475nm
Royal Blue is typically around 450nm
The bandwidth of a Royal Blue stretches out to around 400nm near UVA and hitting the limit of human advisably (about 400nm). Blue does get as close so it is still considered Luminous.
Blue is visible so measured in Luminous units typically lumens.
Some of Royal Blue wavelength spectrum is not really visible. The eye can react to 400nm but it is perceived so much less by the eye Royal Blue is almost always measured in Radiant Units mWatts of flux.
I have seen studies on the photoreceptors in the retinal ganglion cells with a highest sensitivity of 470-490 nm blue light on the effects of short-wavelength light in humans. Several studies have explored the efficacy of monochromatic blue or blue-enriched light in the treatment of syndromal seasonal affective disorder(SAD) and Sub-SAD.
One study, The effects of low-intensity narrow-band blue-light treatment compared to bright white-light treatment in sub-syndromal seasonal affective disorder used a 470 nm, Philips, goLITE HF3320. So we are probably talking Blue not Royal Blue.
To answer your question on comparing mWatts to Lumens it can be estimated.
The perceived brightness, or luminous efficacy, of light is technically specified by the International Commission on Illumination (CIE). Each wavelength efficacy is related to a wavelength of 555nm (Lime Green).
I am only somewhat confident these number are relevant. I do need to have someone else verify they are correct before I publish.
I created this table for common LED colors
What I am going for here is the factor to convert mWatts to Lumens. To convert other colors to the 555nm equivalent output flux, multiply the LED's published lumens by the reciprocal of the CIE factor.
CIE sets the spectral luminous efficacy of the human eye for each wavelength starting a 555nm. The CIE defines photopic vision as 683 lumens/watt at 555 nm.
This I wrote a PHP script to create an SVG image from the table of CIE table of CIE Photopic Luminous Efficacy.
Royal Blue wavelength is 450 where the CIE luminous efficacy is 0.038.
Using the CIE photopic luminous efficacy for 450nm of 0.038 we can convert lumens to the approximate Radiant flux (mWatts):
(lumens÷683) / 0.038 = mWatts
Conversely
mWatts × 0.038 × 683 = lumens
None of this should matter. If you are using Blue (470nm) and not Royal Blue(450nm). Blue is almost always specified in lumens. You should be able to ignore any measured in mWatt.
You probably want either Cree XPE or Lumiled Rebel ES Color LEDs. Which depends on what is available at the time you order them.
Cree
Lumiled
You probably want the ones circled in Red. But you are going to need between 6 and 8 each to reach 250 lumens.
Notice the blue circle on the Lumiled Blue. This is another thing you have to watch out for when comparing LEDs. LEDs are spec'ed out at various currents. The one circled is pumping twice the current of all the others.
Temperature affects luminous flux significantly. Some are spec'ed at 25º C others 85º C.