Warmer whites top DOE's wish list

comozo · Apr 6, 2008

http://optics.org/cws/article/industry/33658;jsessionid=30CCE46490692F9805C50A6DB817ECFC

The research focus on high-performance LEDs will now shift towards more warm-white LED and high-efficacy luminaire development, according to a US Department of Energy report.
DOE targets
DOE targets

The race between top LED manufacturers to deliver ever-increasing luminous efficacy will slow down in 2008 and 2009 as companies refocus on expanding their commercial reach. That's the finding of the US Department of Energy (DOE) 2009-2014 multi-year programme plan for solid-state lighting (SSL), which suggests that efficacy improvements will soon start to tail off.

"There are new things to deal with now that we've got the efficacy up where we'd like to see it," said Fred Welsh of Radcliffe Advisors, who helped prepare the report. "There's now more emphasis in getting warmer white light into commercial products. It's very difficult to sell cool white LEDs into some markets, particularly residential lighting."
The report is put together annually by the DOE with the help of many US-based SSL companies, including Philips' Lumileds division, Osram's US unit and Cree. Interstingly, the efficiency improvements achieved by the industry in 2007 exceeded its predictions.

In September last year, Cree delivered cold-white LED efficacy of 129 lm/W at a colour temperature of 5813 K. It also pushed up the standard for the intrinsically lower efficacy warm-white devices to 99 lm/W at a 2950 K colour temperature.

The DOE report's authors now predict that LED efficacy improvements will slow, before approaching a ceiling of 228 lm/W for cool white and 162 lm/W for warm white devices.

However, the impressive progress in 2007 has increased the overall milestones in the DOE's plan, which now call for 140 lm/W efficacy cool white and 90 lm/W warm white commercial chips by 2010. The report has also introduced a new LED goal that indicates the shift away from device efficacy: to deliver a 126 lm/W efficacy, 1000 lm output luminaire by 2012.

According to Welsh, this represents a growing feeling among the report's authors that more attention should be paid to the specific challenges of designing LED luminaires. "It's easy to ruin a good LED in a [poor] luminaire - and people are doing it," Welsh said. "We're very concerned that will sour the market."

The efficacy target graph from the DOE report, with the red dashed line representing the upper limit for cool-white LED efficacy. The yellow dashed line shows the maximum for warm-white emitters.

2xTrinity · Apr 7, 2008

Intersting. Although, I'd be curious to see how neutral white emitters stack up. As far as color temperature is concerned, they should be right in the middle of the warm and cool white emitters being discussed in this article. However, in terms of matching with our eyes' sensitivity, a neuatrl white emitter should actually have a HIGHER theoretical maximum than a cool white source, since the heavy proportion of blue light doesn't contribute much to the total lumens/watt count.

jtr1962 · Apr 7, 2008

2xTrinity said:
However, in terms of matching with our eyes' sensitivity, a neuatrl white emitter should actually have a HIGHER theoretical maximum than a cool white source, since the heavy proportion of blue light doesn't contribute much to the total lumens/watt count.

Yes. Luminous efficacy of tricolor emitters is maximized at ~400 lm/W right around 4000K according to theoretical studies. I imagine similar numbers would exist for white plus phosphor emitters if new phosphors were to be used, except they would be lowered by the phosphor conversion efficiencies. Even taking that into account, I suspect phosphor LEDs could exceed 300 lm/W in theory with the right phosphors. In practice I'd say figure 80% of these numbers, or 320 lm/W for tricolor emitters and about 240 lm/W for blue plus phosphor.

Seeing the move towards cooler CFLs even in residential markets, I think the DOE has the wrong focus. Probably 3500K to 4500K will be the highest market share of residential lighting. While incandescent type lighting might seem "normal" to most of the consumers over about 50 since that's what they likely grew up with, the younger market segment has gotten used to other types of lighting. This is especially true of those born in the 1990s and later who grew up with small LED lighting devices. Cool light may indeed seem more "normal" to them than warmer light by the time they start making lighting purchases. Just judging by what I see locally, it seems 5000K and even 6500K seems to be catching on as well. I see a lot more of it than I used to. The increasing use of CFLs has bought with it the realization that these things can produce non-incandescent type lighting. It appears many people are experimenting, and some like the results enough to stick with cooler lighting.

Also interesting is how they revised the efficiency targets upwards. With projected power savings of 10 to 1 over standard household incandescents, or 15 to 1 over less efficient small base lamps, adopting LEDs on a large scale is a no brainer. The extremely long lifetime only adds to the appeal.

2xTrinity · Apr 7, 2008

jtr1962 said:
I think the DOE has the wrong focus. Probably 3500K to 4500K will be the highest market share of residential lighting.

I think having lights at least as warm as 3500k range will be critical before we see people start switching to LED lighting for in-home use. As much as I prefer cooler white light sources, theres' a pretty major bias against that among the general public simply because it is different from what they expect. Among older customers, memories of old school magnetic-ballasted fluorescent lighting doesn't help that perception, either.

I just hope the DOE does something so we see more quality control on LED products sold. Most of the LED lamps for sale now are total junk, so early adopters are getting a bad first impression of LEDs in general.

While incandescent type lighting might seem "normal" to most of the consumers over about 50 since that's what they likely grew up with, the younger market segment has gotten used to other types of lighting. This is especially true of those born in the 1990s and later who grew up with small LED lighting devices. Cool light may indeed seem more "normal" to them than warmer light by the time they start making lighting purchases. Just judging by what I see locally, it seems 5000K and even 6500K seems to be catching on as well. I see a lot more of it than I used to.

I seem to see 3500k becoming the most dominant. As it's slightly whiter than incan, but not too different as to be a major clash. Most schools, and offices already use 3500k, and more homes are starting to use them.

The last couple hotels I've stayed in are using 5000k in the rooms, which is interesting. I like 5000k at high intensity for task lighting, especially in offices with windows, as during the daytime it doesn't create a clash with the light coming through the windows.

Also interesting is how they revised the efficiency targets upwards. With projected power savings of 10 to 1 over standard household incandescents, or 15 to 1 over less efficient small base lamps, adopting LEDs on a large scale is a no brainer. The extremely long lifetime only adds to the appeal.

LEDs are particularly good in small applications, as both incan and fluorescent do worse when scaled down to small sizes (ie candelabra base lamps). A "cool burning" alternative to halogen MR16 spotlights is something I know a great deal of people are looking for, and something no fluorescent can ever replace. I actually found CPF while trying to search for an LED like that a couple years ago.

VanIsleDSM · Apr 8, 2008

For daytime or task lighting I also don't mind a whiter colour.. 4000-5000k, but not at night, it's not natural.

As the sun goes down more blue light scatters, that's why you get a more yellow/orange/red sunset and sunrise... after the sun has gone down, I think you want more of a "dusk" time light than daytime light.. More like the ~1500k colour temp of fire or candles that humans have been used to for nighttime lighting. In the home at night.. I like a 2600-3500k.. but in the workshop I use daytime fluoros.

Blue light has been proven to slow melatonin production in your brain.. melatonin helps put you to sleep and relax you.. too much blue light at night can disturb your sleep.. even blue indicator LEDs on electronics in the room can have an effect you may not even notice.. I think our bodies are used to the natural decline in blue light as the sun goes down.. it helps keep us awake during the day, and as it fades we will naturally start winding down for the night.. so I don't think 5000-6500k has any place in a home after sun down. I find warmer light much more relaxing.

jtr1962 · Apr 8, 2008

VanIsleDSM said:
For daytime or task lighting I also don't mind a whiter colour.. 4000-5000k, but not at night, it's not natural.

What about starlight and moonlight? You can't factor fire into the equation here because man hasn't been using it long enough for any evolutionary adaptation to occur. And reddish sunsets/sunrises occur for such a short percentage of the day that any evolutionary adaptation to them wouldn't give any survival advantage. Point of fact fire and candlelight are absolutely horrible for seeing precisely because evolutionarily it wasn't worthwhile adapting to such transient conditions. Sure they're relaxing. You can't really see enough to do anything worthwhile under them, so you just drift off to sleep instead.

Blue light has been proven to slow melatonin production in your brain.. melatonin helps put you to sleep and relax you.. too much blue light at night can disturb your sleep.. even blue indicator LEDs on electronics in the room can have an effect you may not even notice.. I think our bodies are used to the natural decline in blue light as the sun goes down.. it helps keep us awake during the day, and as it fades we will naturally start winding down for the night.. so I don't think 5000-6500k has any place in a home after sun down. I find warmer light much more relaxing.

You're going on the operative assumption that we still go to sleep shortly after dusk and rise at dawn. In that case, you really don't need any type of artificial light at all. The whole point of artificial light is so that societal functions aren't constrained by the hours of the day. In winter especially that would mean a mere 7 or 8 productive hours. The fact is whatever type of light you like in your home is more personal preference than anything else. Why then is 5000K preferred in a lot of Eastern countries? Did they evolve on a different planet? I think not. And sleeping at night isn't natural for everyone. As a night person I actually start getting sleepy when the sun comes up, and sleep easily during the first half of the day.

Intensity is really what determines if light is relaxing or not. I don't think warmer light would be any more relaxing than cooler light at 50,000 lux. The reason we associate warmer light with relaxation has been because warm incandescent light is horribly inefficient. The power to light a room to any reasonable intensity is cost prohibitive. One or two 4x32W T8s will light an average size room nicely. You'll need 1500 or 2000 watts of incandescents to do the same thing. Obviously that would be ridiculous, so we use maybe 100 watts but end up with cave-like lighting. Traditionally we've used only fluorescents where brightness mattered, and only incandescents where it didn't. Had we chosen low-wattage fluorescents instead, the association of relaxation with low intensity, rather than low CCT, would have been clearer. I've tried dimly lighting rooms with white LEDs. To me this is as relaxing and natural as sleeping under the stars. Few people believe it until they actually try it. As a bonus, you can actually see fairly well even at a lower lux level because your scotopic sensitivity peak is shifted to lower wavelengths than the photopic peak. In other words, the apparent lumens are more for a high CCT source. This makes such sources better from an eenrgy efficiency standpoint, which is really the DOE's ultimate goal. I certainly wouldn't want a room lit like a stadium if I was trying to relax, but by the same token I like to have light I can actually see fairly well under regardless of intensity. Low CCT light gives horrible contrast. Things look really fuzzy. Red light is an extreme example where it's hard to get anything into focus at all. I'll even go so far as to say I'm sure the incandescent lamps many have used in their homes have caused all sorts of long term vision problems from the eye lens straining to focus under a type of light it didn't evolve to deal with on a continual basis.

All is not lost though. I think we'll soon have LED fixtures with user adjustable color temperature. This is really the best of all worlds. I wish the DOE would push for this instead of pushing for warmer LEDs.

2xTrinity · Apr 8, 2008

VanIsleDSM said:
For daytime or task lighting I also don't mind a whiter colour.. 4000-5000k, but not at night, it's not natural
...
More like the ~1500k colour temp of fire or candles that humans have been used to for nighttime lighting. /quote]
I greatly prefer the 4200k of a full moon, myself. Too bad that's unnatural

In the home at night.. I like a 2600-3500k.. but in the workshop I use daytime fluoros.

Click to expand...

Agreed. In the house, I use 3500k (the upper end of your range), and in the shop/office, I use 5000k. I would probably use 4000k more, but most lights at that color temp also tend to have low CRI. That should change with next-generation LEDs though.

Blue light has been proven to slow melatonin production in your brain.. melatonin helps put you to sleep and relax you.. too much blue light at night can disturb your sleep.. even blue indicator LEDs on electronics in the room can have an effect you may not even notice..

Click to expand...

If you're reading this post after sunset, I guarantee you your retina is receiving orders of magnitude more blue light from the bright 6500k rectangle you're currently staring at than from any room lights, and ESPECIALLY more than the blue LED on your mouse.

I agre though that some of those blue LEDs are annoyig, I have a few devices in my bedroom that are right at eye-level, which I "fixed" by covering them up with green fluorescent labels/tape. Now obnoxiously bright blue is a soft diffused green. I'd have the same gripe about any colored LED as bright as those were, though -- for some reason, the newer devices just have brighter indicator LEDs.

I think our bodies are used to the natural decline in blue light as the sun goes down.. it h1elps keep us awake during the day, and as it fades we will naturally start winding down for the night.. so I don't think 5000-6500k has any place in a home after sun down. I find warmer light much more relaxing.

Click to expand...

I don't think it's entirely decline in blue light, it has to also be related to the decline in lux/quantity of light in general.

VanIsleDSM · Apr 8, 2008

jtr, You haven't quite got it figured.

Modern man has been around for only about 100,000 years, while sub species of man have been around for 2-3 million years... it's believed that fire was first controlled by a sub species of man about 1,420,000 years ago.. no time to evolve you say?

Red light is not the hardest to focus on, blue light is.. because it doesn't focus right onto the retina, slightly in front.

You say Incandescent lights are horrible for looking at things.. Then why is the CRI (colour rendering index) based on incan bulbs? They score 100, setting the bench mark. Pure white LEDs will generally score 60-70CRI.. while warm white LEDs can be over 90CRI.

There is a reason why most people prefer the light from an incandescent bulb more than anything else... Although warm white LEDs are nearly just as good these days... and most of the time probably indistinguishable to the non lighting-minded person.

You must have also completely discounted what I said about melatonin production in the brain.. I suppose you think this is just some odd coincidence? You're looking right past the evidence.. this is the evolution we've reached from our surroundings.

I just went to wiki to prove my correlation of light to melatonin.. and was surprised by how much they go into depth about it, even speaking of higher cancer rates in night workers who are under bright lights all night.. never produce enough melatonin that acts as a very powerful antioxidant in the body.. check it out yourself.. worth the read..

http://en.wikipedia.org/wiki/Melatonin

I'm glad you challenged what I said.. I've now learned even more about it.. and I'm completely positive that 5000k or 6500k light has no place in a home at night... I didn't understand how much harm too much blue light at night could do to you.

Your intensity being the deciding factor of relaxing lighting theory is completely unfounded.. warmer colours allow more production of melatonin and promote more relaxation.. founded.. proven.

P.S. How about this?.. it's no BS that every 911 call station gets more calls on every full moon.. and many more oddities happen on the full moon.. maybe that extra blue light keeps people up and stirring about.. causing more ruckus.

jtr1962 · Apr 8, 2008

VanIsleDSM said:
Modern man has been around for only about 100,000 years, while sub species of man have been around for 2-3 million years... it's believed that fire was first controlled by a sub species of man about 1,420,000 years ago.. no time to evolve you say?

Yes, that's what I'm saying. Evolutionarily, changes like that happen over tens of millions of years or more, especially in primates with a relatively long time between generations. Also there is NO evolutionary advantage to it. That's my greater point. During the day we have sunlight. At night our eyes see well enough under starlight/moonlight to hunt. Fire for a long time was difficult to make, transitory, and mainly used for warmth, cooking, or scaring away animals, not seeing. There would be zero reason for our eyes to adapt to see well under it. We just didn't use it for that function until we moved north and lived in caves some tens of thousands of years ago. Yes, we probably associated the color of fire with the warmth and safety of being among the tribe, but that's a cultural association, not a evolutionary one.

Red light is not the hardest to focus on, blue light is.. because it doesn't focus right onto the retina, slightly in front.

I'm basing this on my experiments with monochrome LEDs. The reds by far were the worst as far as being able to see any sort of detail or contrast. Maybe focus is the wrong word. I just know red light is horrid for visual acuity, at least with me.

You say Incandescent lights are horrible for looking at things.. Then why is the CRI (colour rendering index) based on incan bulbs? They score 100, setting the bench mark. Pure white LEDs will generally score 60-70CRI.. while warm white LEDs can be over 90CRI.

CRI is not a good measure of light quality. It's only relevant to compare two light sources at the same color temperature. Even there it has limitations. There's actually an ongoing discussion about that in another thread. As for the CRI of warm white versus cool-white LEDs, that has little to do with color temperature. The phosphor used for cool whites happens to have very little red output. A better phosphor which approximates 5500K sunlight could have a CRI close to 100. And not all warm white LEDs have a high CRI. The ones from Lumileds do, but most others are similar to cool whites. They have more yellow phosphor emissions and less blue primary emissions (hence the warmer color) but they're still as deficient in reds as the cool whites. Lumileds used a special phosphor to overcome that problem. They could have easily adjusted the color balance of that phosphor to make a high-CRI cool white LED if they wanted to.

You must have also completely discounted what I said about melatonin production in the brain.. I suppose you think this is just some odd coincidence? You're looking right past the evidence.. this is the evolution we've reached from our surroundings.

It's all interesting stuff but there are so many confounding factors here. For example, most places with artificial light also have high levels of air pollution. Most of the food we eat contains carcinogens as well. It's impossible to really do a controlled study here. If we lived in a pristine environment and ate only natural, pure food then maybe we could say lack of melatonin production causes cancer. Being that I've never liked to sleep in the dark, and in general consider 6 or 7 or 8 AM bedtime, I should be a cancer stick by now. There are plenty of other things that cause cancer, and also plenty of other ways to protect oneself against it. I prefer diet, exercise, taking vitamin supplements to name a few. I'm sure I could take melotonin supplements also. To me that's a far better way to protect myself just in case these studies are correct than living under light I don't like. And that brings me to this:

I'm glad you challenged what I said.. I've now learned even more about it.. and I'm completely positive that 5000k or 6500k light has no place in a home at night... I didn't understand how much harm too much blue light at night could do to you.

You state this as some sort of absolute, that nobody should have this kind of light in their homes at night. That's what bothered me enough to type a long post. Aesthetics and ability to see are two important functions of lighting. I *can't* see well under incandescent light. There is little ability to distinguish cooler colors. Navy blues and black look the same, for example. Furthermore, there is no white point. I just think it makes everything look ugly and yellowed and decayed, not relaxing. In short, it causes a great deal of stress in me. And that's why I hope that DOE doesn't make the same mistake they did with CFLs, namely that getting any color other than warm white from retail stores is close to impossible. That's what peeves me. I don't care what you or someone else wants to use, but I like to have lighting that appeals to my aesthetics as well.

As for the greater number of 911 calls on a full moon, I could come up with any number of plausible theories as to why that is so. Truth is nobody knows yet. Given the amount of light pollution in most areas where people live nowadays, the extra light from a full moon just blends into the background. I don't even notice when there's a full moon. Somehow the moon is making its effect felt in other ways. If I had to guess the reason, I would say we evolved some sort of internal mechanism, perhaps based on magnetism, which stirs us up when there's a full moon. In the prehistoric world, we would have had more success hunting a wooly mammoth or a TRex if we had moonlight to see it with. Evolutionarily it makes a lot of sense to be more active when there's a full moon. We just don't know what the mechanism is yet.

jtr1962 · Apr 8, 2008

Getting back to the main topic, based on these new guidelines, whether banned or not does anyone seriously think incandescent lamps will be around in any way, shape, or form in let's say 3 years? If the price follows the trends of other semiconductors we'll probably have sub-$1 emitters before long which have 125+ lm/W efficiency and last 50,000 hours. I just don't see how anything else can compete with that. For that matter, I see CFLs going the way of the dinosaur very soon also.

LEDependent · Apr 8, 2008

To me, CFLs are the uncomfortable transition stage between incandescents and LED lighting. Like hybrid cars, they will only be around until the transition is made to the newer technology. Incandescents, requiring no circuitry, will never completely die out, especially in cooler climates where their heat can be of use. Financially, it would be difficult to find a compelling reason to replace an incandescent in an old shed with something more energy efficient.

That being said, I prefer T5's and T8's in as many rooms as possible.

-Jason

SemiMan · Apr 8, 2008

Wow... nice thread.... or it could be.....

Thoughts:

- We will have plenty of incandescents (at least halogen) variety 3 years from now. 5 years may be completely different, but 3 yes. LEDS still need to overcome not just efficiency, but cost and heat hurdles, i.e. the ability to put out not just efficient light, but lots of light at high efficiencies. We are not there yet.

- Melatonin production is highly dependant on blue light, period. It has been proven in highly controlled studies. It is really not open for debate. That said, you do not need necessarily to get rid of blue(ish) light whenever it is dark outside, but you may want to consider not having brighter blue lights around near bed time.

- Visual acuity is highly effected by color temperature (not CRI). In fact, the higher the color temperature (to a point), the better your visual acuity. That is because your pupil responds predominantly to the blue in the visual spectrum. Close the pupil and you increase depth of field just like increasing the F-Stop on a camera.

- Higher color temperature lights are perceived as brigther even at lower source lumens. However, that could be as much from the reflectivity of the typical environment.

- 1.3 million years is enough for some evolutionary pressure...check our anthropology texts.... we are different from our ancestors. That said, fire was likely in general for heat, not specifically lighting....given our scotopic sensitivity, which seems pretty well tuned to moonlight, I think you can safely say any evolutionary pressure has favoured moonlight as the light source. I am guessing, but good evidence.

- Actually, people do not prefer high CRI lights all the time. There have been studies that have shown preference for lights that are not high CRI, or warm. They preferred the lower CRI, high CCT light. Also remember that a 100 CRI tungsten bulb is still going to make your colors look "wrong" compared to 100CRI daylight. Your eyes can correct for white pretty well, but they can not correct for the varied reflective spectrums of the objects in the real world. I have repainted in my house after changing lighting.... I like the new lighting, so I changed the paint to get the color I wanted under that light.

Semiman

LEDependent · Apr 8, 2008

SemiMan said:
Also remember that a 100 CRI tungsten bulb is still going to make your colors look "wrong" compared to 100CRI daylight."

This confused me until I looked in up in Wikipedia. Apparently, light sources under 5000K are not compared to sunlight. Instead, they are compared to black-body radiation at their corresponding temperatures. CRI, then, is more of a judge of how close a source is to an ideal black body.

-Jason

Calina · Apr 8, 2008

VanIsleDSM said:
P.S. How about this?.. it's no BS that every 911 call station gets more calls on every full moon.. and many more oddities happen on the full moon.. maybe that extra blue light keeps people up and stirring about.. causing more ruckus.

Interesting discussion! This however is nothing more than a urban legend as serious statistical analysis have proven.

jtr1962 · Apr 8, 2008

SemiMan said:
They preferred the lower CRI, high CCT light.

That's actually interesting. Did the studies also include a high CRI, high CCT light source, and if so why wasn't that preferred over the low CRI, high CCT source? I can definitely understand the preference for a low CRI, high CCT source over a high CRI, low CCT source as I remember preferring old school CRI 60 cool-white fluorescent over incandescent. At least with the fluorescent there was a decent white point of sorts.

Melatonin production is highly dependant on blue light, period. It has been proven in highly controlled studies. It is really not open for debate. That said, you do not need necessarily to get rid of blue(ish) light whenever it is dark outside, but you may want to consider not having brighter blue lights around near bed time.

I wasn't debating that part of it. I was just debating whether or not lack of melotonin production was harmful enough to cause a rise in cancer rates. I personally have no troubles falling asleep and dreaming even with exposure to daylight but then again I only sleep when I'm tired. I don't sleep on a schedule.

jtr1962 · Apr 8, 2008

LEDependent said:
Financially, it would be difficult to find a compelling reason to replace an incandescent in an old shed with something more energy efficient.

That's certainly true. I wasn't saying that nobody will be using incandescents in a few years. Rather, I was saying that I doubt they'll be on store shelves by then. Doubtless lots of people will use up their old stocks of incandescents for utility areas where usage patterns don't justify replacing the lamps with energy efficient ones. We still have an incandescent lamp in a socket in the attic. Being that we hardly ever go up there, it'll only be changed for an energy efficient bulb if/when it burns out.

That being said, I prefer T5's and T8's in as many rooms as possible.

Same here. Outside of chandeliers in the master bedroom, dining room, and living room, and perhaps a dozen CFLs in table lamps or outdoor lamps, we're mostly T8s here. The entire finished basement is T8s with a few T12s. The kitchen and my bedroom have 4x32W T8 fixtures. Hopefully we'll have nice small base LED bulbs for the chandeliers soon. Funny that my mom hates incandescent light also, but she won't part with the chandeliers because "they look pretty". If it were my house they would have all been gone and replaced with 4x32W T8 fixtures.

I don't see LED replacing T8 or T5 anytime soon though. Most businesses only replace fixtures on a 20 to 25 year cycle. Seeing that many local businesses have T8s for 5 years or less, it'll probably be at least 15 to 20 years before they go fo LED fixtures.

2xTrinity · Apr 8, 2008

SemiMan said:
Wow... nice thread.... or it could be.....

Thoughts:

- We will have plenty of incandescents (at least halogen) variety 3 years from now. 5 years may be completely different, but 3 yes. LEDS still need to overcome not just efficiency, but cost and heat hurdles, i.e. the ability to put out not just efficient light, but lots of light at high efficiencies. We are not there yet.

I suspect it will be at least 15 years before we start to see incans disappear on a wide scale. Consider that many were expecting high-definition TV in the early 90s, and the technology existed even then, yet HDTV is still in the "early adopter" phase in 2008.

- Melatonin production is highly dependant on blue light, period. It has been proven in highly controlled studies. It is really not open for debate. That said, you do not need necessarily to get rid of blue(ish) light whenever it is dark outside, but you may want to consider not having brighter blue lights around near bed time.

Good point, cool white is a bad choice for night-lights. I think the point that some like JTR and myself are worried about is that the government will only explicitly encourage <3000k warm white, to the point where it is very difficult for those who want to to purchase higher color temperature lighting to find it.

If I am trying to actually do work though, I specifically don't want to sleep. Also, If I'm going to be using a computer, all this talk about inhibiting blue light is completely moot -- computer monitor are 6500k, and FAR brighter in my field of vision than any room lights... and before anyone suggests it, no, I'm not going to disable the blue component in my monitor. I'd probably get more ill from trying to work with a brown monitor than from the lack of melatonin :sick2:

- Visual acuity is highly effected by color temperature (not CRI). In fact, the higher the color temperature (to a point), the better your visual acuity. That is because your pupil responds predominantly to the blue in the visual spectrum. Close the pupil and you increase depth of field just like increasing the F-Stop on a camera.

Another factor is that of all the monochrome wavelengths, our eyes have the best acuity with green light. Neutral white light sources have the greatest percentage of green light output relative to the other colors.

In my case, all these effects are somewhat exaggerated too, as I have astigmatism. While my eyes focus perfectly with predominately green light, they do somewhat worse with predominately blue light (>5000k), and much worse with predominately red light (<3500k). My astigmatism also means I get a more pronounced benefit from the "pupil constriction" effect.

- Higher color temperature lights are perceived as brigther even at lower source lumens. However, that could be as much from the reflectivity of the typical environment.

At low intensity, our eyes shift toward being more sensitive to blue light. Also, our peripheral vision is also a lot more sensitive to blue light than other colors. The lumen scale only refers to center of field of vision, in photopic (bright) conditoins, so a blue light that is fewer lumens than a red light can actually appear far brighter in a dark environment.

Once my night vision has become adapted, I can light an entire trail bright enough to hike comfortably using less than 1/4 lumen from a cool white LED. In order to see equally well with red light, I need over 100 lumens.

- Actually, people do not prefer high CRI lights all the time. There have been studies that have shown preference for lights that are not high CRI, or warm.

This false dichotomy between Warm/High CRI and Cool/Low CRI has only existed because up until very recently, the only "cool white" artifical lighting has been poorer quality fluorescent and HID sources. Once we start getting nearly-perfect CRI cool and neutral LEDs on the market, I believe people who give them a chance will prefer those over everything else.

Warmer whites top DOE's wish list

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