I found this interesting page on Cree site: http://www.cree.com/About-Cree/History-and-Milestones/Milestones
They announced a 303 lumen/watt LED "at research&development level" back in 2014.
In currently available LEDs on Cree site I was not able to find anything with more than 180 lumen per watt, did anybody have better luck?
Which is the current "Cree state-of-the-art" for LPW density?
I have not looked at the article, but lumen/watt is closely related to color rendering.
The eye is most sensitive around the yellow color, i.e. a yellow lamp can have a very high efficiency (Like a yellow street lamp).
When the color rendering improves the lumen/watt will go down.
well, i remember that eyes is most sensitive to green color, that’s why the same power, the green laser is brighter than other color
correct me iif i’m wrong
The correct wavelength is 555nm, that’s around where green turns into yellow, but to the green side.
Just fyi, the lower current you drive an LED, the higher lumens/watt you get.
For example,
Theoretical maximum for phosphor converted white light LED is around 300lm/W: White LEDs with super-high luminous efficacy could satisfy all general lighting needs
This wikipedia article is very informative: Luminous efficacy
We are already very close to that limit on the lower side of the current. You have to remember that LED efficacy drops inversely with current so in reality finding LED with more than 180 lm/W efficacy is quite easy.
According to Cree Product Characterization Tool XP-L2 HD W2 at 350mA has 211.6 lm/W, no data for lower currents but those values would be much higher. XP-G3 S6 at 100mA has 236.5 lm/W so efficacy at 10mA, not to mention 1mA, would be even higher…
Common XM-L2 LEDs in U3 bin exceed 200lm/W at 160mA.
Never understood that, because why then is 580 nm pure yellow the brightest colour to our eyes?
See?
Jerommel, see here: Photopic vision.
It’s determined by pigment absorption maximums in the eye and theirs superposition.
In the above picture yellow part might seem brighter just because it is 
It’s just some rainbow color picture - nothing guarantee uniform brightness and display device characteristics also play big role in picture perception.
That’s fine with me, but still yellow is the brightest to our eyes.
Well, to mine anyway…
And not only in that colour wheel i posted, but with any illuminated object.
…so i still don’t get it… (but that could be me…)
If you would compare two uniform sources (say monochrome lasers) with same power used, green would be brighter.
What you are talking about is not a light source but merely light reflected from some surface. Yellow in the picture might seem brighter due to many reasons.
Even when you compare cheap laser pointers it’s very clear green is the brightest and is visible from furthest distance. Yellow laser pointers are uncommon and thus expensive though…
It’s actually green.
You have more green cones in your retina.
This is why night vision equipment colours stuff in green, your eyes can distinguish more shades of it.
What is actually green?
What to our eyes is the brightest colour, with what monochromatic colour of light do we see best?
Let me just speak for myself then: It’s yellow.
A yellow object is of brighter colour than a green object.
Why are yellow lights used for highway lanterns and even headlights?
Probably because we see best with yellow illumination.
So i’m not sure if the technical explanation is as relevant as you think.
(or i’m frustrated i don’t understand it…)
Meh…
Yellow lights are used because street lights are mostly sodium lights, which mostly emit 589nm light (amberish yellow). Also, yellow to red tints are much less straining to our eyes than blue-green ones.
Also, the 555nm number is an average, but I think 580nm is wayy off average.
The reason yellow is brighter on our monitor is because yellow is made from red+green on your monitor, so you have twice as much light than just green. Lastly, our monitors are balanced to have colors of the same brightness, so there may just be less green emitted.
It’s not yellow, it’s low temperature white.
It emits light on all wavelengths so that you can see all colours.
It just happens that older technologies like sodium or filament lamps emit more green and red than blue, which results in a yellowish colour.
If it was yellow, you would only see everything in yellow.
This is what yellow headlights look like:
I don’t know about you, but I have never seen irl a headlight or street lamp with yellow colour.
Just like with yellow, it would be a pain to have green lighting, because again you would not be able to see any colour.
I’m not on about my monitor.
But a decent monitor does represent reality.
And in reality yellow is brighter than green, even brighter than yellowish green.
At least, to my eyes it is…
So why do you think Sodium (Natrium) lamps were such a success? They’re still used today.
Have you seen fields of sunflowers in bloom in real life?
I mean, i can’t believe we’re even discussing what is the brightest colour in human perception…
Why do we disagree?
There must be something we forget to take into account…
No, Sodium lamps are quite monochromatic.
There are 2 narrow bands of yellow in the sodium lamp spectrum, and a bit of red from the mercury to start it up.
With Sodium lamps everything IS in shades of yellow.
No red (well, maybe a tiny bit of the mercury), no green, no blue.
Yellow incandescent headlights only have a yellow coating on them, basically blocking the blue.
It’s because you have plenty of ambient lighting around and yellow has high contrast.
Also, your monitor is calibrated so that all colours are almost the same brightness, so you’re getting a biased view anyway.
If you compare yellow in green under identical conditions, green is brighter because the retina has the most green cones.
“The laser which will appear brightest will be of that color (wavelength of EM wave) to which sensitivIty Of the eye is maximum. That color happens to be green for the human eye. Under appropriate illumination (day) the sensitivity of the eye is maximum for 555nm that is a shade of green-yellow. Under dark conditions (night) the sensitivity if maximum at 507nm which is a shade of green.
So if you have three lasers of different colours which produce beams of the same intensity, then the GREEN-YELLOW or GREEN laser will appear brightest depending on ambient illumination.”
There have been tests done, and the minimum observable difference is lower for green than any other colour.
This is a proper test done in a pitch black room to detect the minimum amount of light needed to be visible. It is not an opinion of what is brighter based on some biased light source.
Obviously if your monitor reproduces colours with green at 50, and yellow with green at 50 and red at 25% then yellow will appear brighter because there is more light entering your eye.
PS: It’s especially the low pressure Sodium lamp that is monochromatic yellow, around 590nm (slightly amberish).
Well, no actually…
If the colours are indeed calibrated to the same brightness, then why is yellow brighter than green?
Sounds very true, but it isn’t… (somehow)…
Maybe it has to do with the blue receptors, which (iirc) make us perceive light as less bright.
For example:
When you shine a blue light on a white wall which is illuminated by white light, the blue dot may look less bright.
Obviously it is not less bright when you add more light, but we perceive it as a darker spot, because our vision does that with blue.
…something like that…
…yeah, i think that must be it.