How close are we to the maximum _perceived_ brightness?

Nereus

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Moving from Luxeon 3 to Cree XRE we have seen roughly 100% increase in led efficiency: lumens have doubled, keeping watts at the same level. But remember, human eye reacts logarithmically to light intensity. You have to double the lumens to _feel_ the light clearly brighter.

So where are we now? Some 25% of electricity pumped in to led will be transformed to light. One "wow this _looks_ brither" step upwards in efficiency means 50% efficiency. Again second (highly hypothetical...) step like this will take us to the absolute maximum, 100% efficiency.

To sum up, when it comes to the way human eye actually perceives brightness we are only one or two "wow this _looks_ brighter" steps or "lux3 -> Cree XRE" steps from the best possible. That's very close after all!

-N
 

kh74

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Point Cree XR-E straight to your eye and you are already there...
 

Tremendo

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As we here know how dangerous a 400+ lumen light can be in a notice's hands, I wonder how far technology will go for popular flashlight use. 40 - 60 lumens is enough for most of my uses, but I like having 100+ handy, if needed. I don't think I need 400+ lumens in my pocket EDC. Oh yeah, I'll buy it, but I don't think it's commercialy viable.
 

Curious_character

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I'm kinda new to this light business, so please help me out.

A P1D CE is the only Cree light I have so far. On high, it drains a CR123A cell in about 45 minutes, so the current is somewhere around 1.5 amps. At 3 volts, that's 4.5 watts. Other folks in this forum have estimated the output at 110 lumens. So that light is producing about 110 lumens/4.5 watts = 24.4 lumens/watt. A lumen is 1/685 watt at 555 nm, so if the P1D CE were producing all its light at 555 nm (which of course it isn't), its efficiency would be 24.4/685 = 3.6%.

Now, that's a far cry from the 25% figure in the original posting. Are there lights that put out 7 times as much light as my P1D CE for the same power consumption, or is there an error in my calculations? I'd be very appreciative if you'd show how you arrived at the 25% figure, or show me where I can get one of those 25% efficient lights!

c_c
 

65535

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Error in calculations and other factors like the fact that different wavelengths and a good mixture will make a better brighter seeming light. ATM the highest efficiency lights are HID
boasting over 100l/w using about as much energy as 2 Cree xlamps you get about 4 times the light and these are the lower end 10w Wolf Eyes when compaired to some of the best like the helios you get 40watts and 4000 lumens. So I pick HID as my future light.
 

tigermoth2000

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I just checked your calculations, I found a slightly dif constant for the conversion, But its D.P's – I wonder though this assumes that the LED emits only at one frequency, it's really a BW output, I suppose that this would give a higher efficiency reading – it should be taken into account as we can see it.
Some of the losses are in light, at a lower? Freq than the eye can see, and Heat, where does the rest go to, the driver? What sort of efficiency does the P1D's run at?
I didn't think that LED's are that inefficient! What sort of efficiency does an Incan give?

Joe.
 

jtr1962

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Curious_character said:
I'm kinda new to this light business, so please help me out.
A P1D CE is the only Cree light I have so far. On high, it drains a CR123A cell in about 45 minutes, so the current is somewhere around 1.5 amps. At 3 volts, that's 4.5 watts. Other folks in this forum have estimated the output at 110 lumens. So that light is producing about 110 lumens/4.5 watts = 24.4 lumens/watt. A lumen is 1/685 watt at 555 nm, so if the P1D CE were producing all its light at 555 nm (which of course it isn't), its efficiency would be 24.4/685 = 3.6%.
Under that kind of load the average voltage of a CR123A sags to something like 2.7 volts. Also, when pulling 1.5 amps a CR123A doesn't get anywhere near its rated mAh. Probably it gets maybe 800 mAh. Therefore, with a runtime of 45 minutes and 800 mAh from the battery you're pulling roughly 1.05 amps. At 2.7 average volts this is about 2.8 watts of power. 110/2.8 = 39.3 lm/W. To get 110 lumens out the front the Cree is probably driven at around 700 mA. With a typical Vf in the 3.4V area then the converter is feeding the LED about 2.4 watts. The difference between that and the input power of 2.8 watts is converter losses. Furthermore, in order to get 110 lumens out the front end the Cree is probably making around 135 lumens. For the LED itself then you get an efficiency of 135/2.4 = 56.3 lm/W.

Now to calculate the conversion efficiency you need to integrate the output spectrum of the Cree to get the luminous efficacy (not the same as efficiency). For blue plus phosphor white LEDs this comes out to about 330 lm/W. Only monochromatic green at 555 nm would be 685 lm/W. Therefore, you get an efficiency of 56.3/330 or 17%. However, running the Cree at 350 mA does indeed give you from about 22% to 25% efficiency. If you want to account for converter and reflector losses in your P1D CE then you end up with 39.3/330 or 11.9% (the 39.3 figure was derived in the first part of the paragraph above).

Yes, we still have a long way to go to get to 100%. However, if we underdrive a Cree we can get maybe 100 lm/W at 60 mA. Couple that with a 99% efficient converter and a 90% efficient focusing system (both possible), and we can end up with roughly 90 lm/W or 27% out the front end. In a year or two when the 145 lm/W Crees are out it should be possible to obtain greater than 50% out the front end by underdriving them.

Another thing worth noting is that the phosphor conversion to white light is a best about 80% efficient so using blue plus phosphor the most we can attain is 80% efficiency, or around 265 lm/W. This assumes a 100% efficient blue emitter. More likely we'll only achieve 75% so blue plus phosphor whites will top out at around 200 lm/W (note that we're already three quarters of the way there in the lab). With RGB we can theoretically achieve 100%. By choosing the proper center wavelengths for each color we can achieve a luminous efficacy for the emitted spectrum of up to 400 lm/W. Even if we ultimately only reach 75% efficiency this means 300 lm/W white LEDs.
 

2xTrinity

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65535 said:
Error in calculations and other factors like the fact that different wavelengths and a good mixture will make a better brighter seeming light. ATM the highest efficiency lights are HID
boasting over 100l/w using about as much energy as 2 Cree xlamps you get about 4 times the light and these are the lower end 10w Wolf Eyes when compaired to some of the best like the helios you get 40watts and 4000 lumens.
The bottom line here is that the LEDs will be best off for low-intensity applications, suhc as compact lights, and the HID is best for high output, such as flood lighting, street lighting, etc. LEDs get more efficient at low power, while HID gets more efficient at high power.

A P1D CE is the only Cree light I have so far. On high, it drains a CR123A cell in about 45 minutes, so the current is somewhere around 1.5 amps. At 3 volts, that's 4.5 watts. Other folks in this forum have estimated the output at 110 lumens. So that light is producing about 110 lumens/4.5 watts = 24.4 lumens/watt. A lumen is 1/685 watt at 555 nm, so if the P1D CE were producing all its light at 555 nm (which of course it isn't), its efficiency would be 24.4/685 = 3.6%.

Now, that's a far cry from the 25% figure in the original posting. Are there lights that put out 7 times as much light as my P1D CE for the same power consumption, or is there an error in my calculations? I'd be very appreciative if you'd show how you arrived at the 25% figure, or show me where I can get one of those 25% efficient lights!
I believe white light at 5000k color temp is around 350 lm/watt, as opposed to 685 for green, making your light closer to about 7%. Also, the efficiency of Cree emitters varies dramatically by bin. Their oldest bin is rated at 65 lm/W at 1W output, their latest at about 95, that's a massive difference. Keep in mind that at 3 watts you're expected to get double the brightness of 1 watt, so efficiency goes down by a third. Also, in the case of your flashlight, I'd guess there are significant losses for voltage converters, and Battery internal resistance loss is also a big one, as that will increase with the square of your current. The lenses and reflectors also cut total light output by about a quarter as well (I'd expect this loss to be higher for HID though)

I wouldn't be surprised if your lumens per watt on low or medium brightness are more than triple what they are on high, or around 21%+ efficiency
 
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chris_m

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65535 said:
ATM the highest efficiency lights are HID
boasting over 100l/w using about as much energy as 2 Cree xlamps you get about 4 times the light and these are the lower end 10w Wolf Eyes when compaired to some of the best like the helios you get 40watts and 4000 lumens. So I pick HID as my future light.

Errors in your calculations! I checked the Wolf Eyes website, and they're only claiming 550lm for their 10W light so only 55lm/W. Yes you'll get better efficiencies with higher powered lights, but down around the 10W mark I doubt HID will get much better and will soon be overtaken by LED (they're very close right now for overall system efficiency if you take real figures including ballast losses etc.)
 
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