Why LEDs Make Us Blue!Recently (February 2015) LD+A published an article by James Brodrick titled "How Safe is the Light from LEDs?" Broderick is the lighting program manager for the U.S. Department of Energy Building and Technologies Office. The article was based on a new "Factsheet" from the DOE, "True Colors" which partially recycles some of the information from DOE's earlier "Optical Safety of LEDs." You can find the original factsheets at www.energy.gov/eere/ssl/technology-factsheets or www.ssl.energy.gov/factsheets.html. You will have to hunt for them by title. DOE doesn't make them easy to locate.
We glean several points from the article and the DOE publications it was based on. First we get an accurate description of "white" LEDs and how they work. "The predominant method used for creating white light with LEDs is to use a blue LED and convert a portion of the emission to longer wavelengths using phosphors. The same approach is used with fluorescent lighting, although the initial emission is in the UV, instead of blue." - DOE "Optical Safety of LEDs" June 2013.
Second, the literature gives us a good technical descriptor of the light source; "blue-pump, phosphor converted LEDs." Marketing types will continue to use the generic "white LED" and maybe provide a color temperature. You should, however, always think "blue-pump, phosphor converted LED" and ask for a spectral power distribution to determine just how blue it is.
Third, Brodrick and DOE acknowledge that "LEDs do have a unique "signature" peak in the short-wavelength "blue" region of their SPDs, around 450 nm, with a broader peak somewhere between 550 and 600 nm" and that "Light in this range (400-500 nm) is known to cause retinal damage with too much exposure... and to have greater potential to damage artwork than light at longer wavelengths."
We want to point out that this is a description of the physics and nature of the LED. Blue-pump, phosphor corrected LEDs will always have that blue signature peak just as fluorescents will always have a significant UV output. It is inherent to the nature of the source. Absent inventing a totally new source, it can not be designed around or corrected.
Recognize, too, that the acknowledged greater potential for damage by blue light is why NARA (National Archives and Records Administration) has set an absolute 500nm cutoff for illumination of our U.S. charter documents (Constitution, Declaration of Independence, Bill of Rights, etc.) While this may seem primarily important to the museum community, light damage can have a tremendous negative impact and create huge costs in retail applications. Losses due to light damaged merchandise or reduced sales due to poor presentation and color can easily offset prospective energy savings.
The surprising things are Brodrick's (and DOE's) arguments after acknowledging all of these points about LEDs. They go like this; "just because most LED light sources have a blue peak in their SPDs doesn't mean they emit more blue light in total, or that they necessarily have more potential to cause retinal, material or photo-biological harm." Say again?
O.K., just because LEDs by nature have proportionally more blue light than other sources, you can dim them so that they actually end up with less total blue light than other sources. That's kind of what I though he said! Adjust the volume not the mix! Get things dim enough and any color is safe.
Brodrick goes on, "...in fact, those risks are about the same for typical commercially available LEDs as they are for other light sources having the same CCT." Lets put that into English. LEDs have a "unique" blue peak, but they are no more dangerous that any other light source of the same blue color. Right!
Last, the DOE (Brodrick is just their spokesman) says that "blue-pump LEDs were generally found to be the least likely product type to cause material degradation... and posed no more threat that a typical (unfiltered) incandescent lamp." Even if that were true, its a terrible endorsement! Unfiltered incandescents cause 20 to 100 times the photochemical and photomechanical damage (material degradation) compared to sources like NoUVIR with a perfectly balanced SPD and no UV or IR.
The actual DOE factsheet states, "While the difference between LED products can be substantial (up to 26%), none of the products exceeds blackbody radiation by more than 8% for any of the risks considered." Since the DOE equates blackbody radiation with incandescent and halogen filaments, they are in fact saying that none of the LEDs they tested posed more than an 8% greater risk for "retinal, material or biological harm" than an unfiltered track light. We might buy that comparison for material (museum) damage although an 8% greater risk is probably low. It depends on just how much dimming DOE did to lower the blue spike in the SPD for their tests.
Regarding blue light hazard and retinal damage, the jury is still out. Like the rest of the industry, we'll have to wait for the class action lawsuits for definitive answers. We rather expect to see television commercials stating, "Did you or a loved one suffer macular degeneration or vision problems after working under LED lights? You may be entitled to damages. Call Duey, Cheatham and How at 888-555-5555." Unlike you, me or our companies, DOE is, of course, protected from such lawsuits.