No, efficiency is not similar with brightness. I suspect the most efficient leds today are rather weak. Those Cree products are not available, and most brand name ones are too expensive to play with.
Have you measured the light output of the jumbos, or their cone angle? How did you manage to converge the 3 colour beams to the DLP chip? And finally, did the pwm and synchronisation work, or was it all just a simple single led preliminary test?
With merely 1 lm I can watch movies quite acceptably on a 1.5m diagonal screen, in a darkened room. 100lm is already luxury, keeping in mind they sell some models with just 11lm.
Have you measured the light output of the jumbos, or their cone angle? How did you manage to converge the 3 colour beams to the DLP chip? And finally, did the pwm and synchronisation work, or was it all just a simple single led preliminary test?
With merely 1 lm I can watch movies quite acceptably on a 1.5m diagonal screen, in a darkened room. 100lm is already luxury, keeping in mind they sell some models with just 11lm.
Hi zzonbi,
It was just a very early test of five of the white LEDs. I didn't buy any red, green or blue LEDs yet as I wanted to test the brightness of those Jumbo LEDs....
I'm no expert on LEDs, but they don't seem to be as bright as you might expect from the ratings.
Obviously, I was only using five LEDs for the test, but I was hoping for them to be brighter than they were. I will probably require a lens to get the most out of them anyway, as the area of the colour wheel section that the original lamp focused on is very small.
I don't have any sort of light meter, and I don't know much about optical stuff. The cone angle is surprisingly narrow on the Jumbo LEDs though, it's just a shame they're not as bright as I expected.
1 lumen! Surely not! I didn't think you'd light up more than a stamp sized image with that, even in a dark room!?
I emailed Edison Opto earlier about their LED engines, and I've already had a reply back. I'll keep you updated, but I don't have any prices as yet.
It was just a very early test of five of the white LEDs. I didn't buy any red, green or blue LEDs yet as I wanted to test the brightness of those Jumbo LEDs....
I'm no expert on LEDs, but they don't seem to be as bright as you might expect from the ratings.
Obviously, I was only using five LEDs for the test, but I was hoping for them to be brighter than they were. I will probably require a lens to get the most out of them anyway, as the area of the colour wheel section that the original lamp focused on is very small.
I don't have any sort of light meter, and I don't know much about optical stuff. The cone angle is surprisingly narrow on the Jumbo LEDs though, it's just a shame they're not as bright as I expected.
1 lumen! Surely not! I didn't think you'd light up more than a stamp sized image with that, even in a dark room!?
I emailed Edison Opto earlier about their LED engines, and I've already had a reply back. I'll keep you updated, but I don't have any prices as yet.
Hello
>The cone angle is surprisingly narrow on the Jumbo LEDs though, it's just a shame they're not as bright as I expected.
That is good for our purposes. It is easy to spread out the light, but impossible to do the opposite.
>1 lumen! Surely not! I didn't think you'd light up more than a stamp sized image with that, even in a dark room!?
1lm (at the screen) is enough light if the other lights are under that level. It's a far cry from quality cinema, but you can follow a movie with some effort. Subtitles can also be read. The trick is to improve the picture adjusting gamma, brightness and contrast levels. Reducing the blue component helps. I do that with powerstrip, from some user defined hot keys.
If you want to measure the cone angle project at a larger distance (1m or more), for better precision. Than just measure the diameter where the light is 1/2 less bright than in center. For a lm measuring you'd need a luxmeter (30$), perpendicular to the light source. A cheaper photodiode can also be adapted, but it's harder to calibrate. It would be interesting to know how much are the specs exagerated.
I'm still searching for a decent small screen, but it looks impossible to find, to the point I'd rather buy a DLP projector alltogether. It looks like the trend in LCDs is to make them sequential too. With no color filters they triple both resolution and light output.
Those flat leds look interesting as an add on to a normal LCD monitor, without ruining it for everyday computing. I'd need just a small patch of them, like 100cm^2. Perhaps even RGB.
>The cone angle is surprisingly narrow on the Jumbo LEDs though, it's just a shame they're not as bright as I expected.
That is good for our purposes. It is easy to spread out the light, but impossible to do the opposite.
>1 lumen! Surely not! I didn't think you'd light up more than a stamp sized image with that, even in a dark room!?
1lm (at the screen) is enough light if the other lights are under that level. It's a far cry from quality cinema, but you can follow a movie with some effort. Subtitles can also be read. The trick is to improve the picture adjusting gamma, brightness and contrast levels. Reducing the blue component helps. I do that with powerstrip, from some user defined hot keys.
If you want to measure the cone angle project at a larger distance (1m or more), for better precision. Than just measure the diameter where the light is 1/2 less bright than in center. For a lm measuring you'd need a luxmeter (30$), perpendicular to the light source. A cheaper photodiode can also be adapted, but it's harder to calibrate. It would be interesting to know how much are the specs exagerated.
I'm still searching for a decent small screen, but it looks impossible to find, to the point I'd rather buy a DLP projector alltogether. It looks like the trend in LCDs is to make them sequential too. With no color filters they triple both resolution and light output.
Those flat leds look interesting as an add on to a normal LCD monitor, without ruining it for everyday computing. I'd need just a small patch of them, like 100cm^2. Perhaps even RGB.
So, are lumens the measure of the power density at any point on the screen then? I'm still learning about all of this.
As for finding a screen. My brother-in-law is using an InFocus X1 with a £20 (~$38?) white roller-blind from Ikea!
If you can find something similar in Spain, it should make a pretty good screen for the money, and way better than my old "tobacco coloured" 2m motorised screen from a pub. The only thing you might want is to put a black border around it.
The LED modules look a bit expensive for using as a backlight, as you'd need quite a few of them without some sort of light guide. We still have hope for using them in commercial projectors though.
As for finding a screen. My brother-in-law is using an InFocus X1 with a £20 (~$38?) white roller-blind from Ikea!
If you can find something similar in Spain, it should make a pretty good screen for the money, and way better than my old "tobacco coloured" 2m motorised screen from a pub. The only thing you might want is to put a black border around it.
The LED modules look a bit expensive for using as a backlight, as you'd need quite a few of them without some sort of light guide. We still have hope for using them in commercial projectors though.
The lumens show an amount of light (flux), whereas candelas show its density (more corectly intensity). Uniform unidirectional rays of 1 candela over 1 square meter amount to 1 lm. Or spherically divergent 1cd rays in 1 steradian cone.
Actually I meant the screen at the other end, the smaller one 😉
Actually I meant the screen at the other end, the smaller one 😉
Hey, I see you're online.
Here's some more of my "teaching": the lux is roughly the equivalent of cd/m^2, but it refers of illuminated areas, while the other one of illuminating ones, ie with self luminance. So we see CRTs specced in cd/m2, and projection screens, or recommendations about room illumination in lux. A good lux value for a study room is at least 50lux, so I guess I'm streching things with merely 1lm over >1m2, but there's another catch: in low light the eye self calibrates in a high sensitivity mode (scotopic vision, by rod cells), with reduced colour perception though. I compensate a bit by maxing out the saturation (nVidia drivers have an option called "vibrant colour"). Before I had my mega lens I watched even lumen fractions in almost black and white. So if you're not spoiled by superbright commercial projectors beforehand it's easier to accept a puny led projection 🙂
Here's some more of my "teaching": the lux is roughly the equivalent of cd/m^2, but it refers of illuminated areas, while the other one of illuminating ones, ie with self luminance. So we see CRTs specced in cd/m2, and projection screens, or recommendations about room illumination in lux. A good lux value for a study room is at least 50lux, so I guess I'm streching things with merely 1lm over >1m2, but there's another catch: in low light the eye self calibrates in a high sensitivity mode (scotopic vision, by rod cells), with reduced colour perception though. I compensate a bit by maxing out the saturation (nVidia drivers have an option called "vibrant colour"). Before I had my mega lens I watched even lumen fractions in almost black and white. So if you're not spoiled by superbright commercial projectors beforehand it's easier to accept a puny led projection 🙂
Do you need less LEDs to illuminate a smaller LCD or is it just the more LEDs you can squish in the better? I just bought one of those 64 LED light bulbs from besthongkong just to test the illumination of my little 1.?inch gameboy LCD. The bulb is more than the size of the LCD but I don't understand the whole science of light spread over an area.
post 203
"perpendicular to the light source" should be "facing the light source, and parallel to the screen". I guess that's how they calculate the ANSI lumen ratings, in different points of the screen, averaged and divided by screen area.
"perpendicular to the light source" should be "facing the light source, and parallel to the screen". I guess that's how they calculate the ANSI lumen ratings, in different points of the screen, averaged and divided by screen area.
No, unfortunately not. You need to squish the same light energy if you want the same end result, on an equal projection screen, regardless of LCD size. That is assuming LCDs have equal transparencies, and the TFTs non dedicated for projections are usualy worse as they get smaller.
hi killerofangels, you need a lens of some sort, can be plastic as you're using a cool light source
measuring screen brightness
This is the ANSI standard method:
Divide the screen area into nine identical area rectangles, in a 3 by 3 grid. Project a 100% white image on the screen in a completely dark room. Measure the LUX value (using a calibrated LUX-meter) at the center of each of the rectangles. Add all nine values together and divide by 9. This gives you the average LUX value. (Identical values would be ideal, but very unlikely!)
If you had a 1 square meter screen image, then the LUMENS would be the same as the average LUX. To calculate:
LUMENS = average LUX * screen area in meters squared
If you get 100 LUX in the center of your screen, then you will have a very watchable image in a dark room. If you have a lot less, then you can improve it by moving the projector closer (or adjusting a zoom lens) to get a smaller image.
This is the ANSI standard method:
Divide the screen area into nine identical area rectangles, in a 3 by 3 grid. Project a 100% white image on the screen in a completely dark room. Measure the LUX value (using a calibrated LUX-meter) at the center of each of the rectangles. Add all nine values together and divide by 9. This gives you the average LUX value. (Identical values would be ideal, but very unlikely!)
If you had a 1 square meter screen image, then the LUMENS would be the same as the average LUX. To calculate:
LUMENS = average LUX * screen area in meters squared
If you get 100 LUX in the center of your screen, then you will have a very watchable image in a dark room. If you have a lot less, then you can improve it by moving the projector closer (or adjusting a zoom lens) to get a smaller image.
parallel LEDs
Just in case anybody is still interested, the reason you don't hook LEDs in parallel is because they are each very similar to zener diodes: If you apply a particular current to an LED, it will drop a certain amount of voltage. If you apply a particular voltage, it will pass a certain amount of current. If you increase that voltage just a bit, it will pass much more current. It is non-linear because it is a PN junction, and not a resistor. If you apply a voltage to two LEDs in parallel, they will pass different amounts of current because their junction characteristics will not match. If you increase the voltage to try to get the dimmer LED to full brightness, the brighter one will pass so much current it may self-destruct.
If you want to run a whole bunch of LEDs, you can drive each one through its own resistor, or you can string them in series and use a single resistor. The resistor drops the voltage that is left over by the LED(s). Since the resistor is linear (Ohm's law) it will always drop the same volts per amp, and if the LED junctions decrease their voltage drops (ie. from heating up) then the resistor will protect them from thermal runaway by dropping more voltage.
Just in case anybody is still interested, the reason you don't hook LEDs in parallel is because they are each very similar to zener diodes: If you apply a particular current to an LED, it will drop a certain amount of voltage. If you apply a particular voltage, it will pass a certain amount of current. If you increase that voltage just a bit, it will pass much more current. It is non-linear because it is a PN junction, and not a resistor. If you apply a voltage to two LEDs in parallel, they will pass different amounts of current because their junction characteristics will not match. If you increase the voltage to try to get the dimmer LED to full brightness, the brighter one will pass so much current it may self-destruct.
If you want to run a whole bunch of LEDs, you can drive each one through its own resistor, or you can string them in series and use a single resistor. The resistor drops the voltage that is left over by the LED(s). Since the resistor is linear (Ohm's law) it will always drop the same volts per amp, and if the LED junctions decrease their voltage drops (ie. from heating up) then the resistor will protect them from thermal runaway by dropping more voltage.
good info, Guy Grotke !
thanks for cutting through some of the confusion
so lux is a spot measurement, and lumens an average per metre squared ?...makes sense now
thanks for cutting through some of the confusion
so lux is a spot measurement, and lumens an average per metre squared ?...makes sense now
Yes, that was very informative. Thanks Grotky!
Just wondering if anyone knows what type of LED arrangement they use in those new commercial LED projectors like the Toshiba TDP FF1? They seem to indicate it's some kind of RGB LED if I'm not mistaken. Would there be any benefit to using an RGB LED grid with a controller to match the video feed (to match luminance behind the LCD, not produce pixels)?
throwit - I have a lense. It's a short throw NEC projection lense. I've gotten a dim image on the wall about 10 feet from the lense just by holding a normal gameboy behind it. The focal point of the lense is very short (22mm) so a larger LCD is out because even the 1.x inch gameboy screen goes blurry around the edges. I'm hoping I can fix this after making the projector housing by using the three adjustment rings on the lense. Anyone know what each ring is for? The thing came with no documentation and it's hard to adjust while holding all the components perfectly still. Exciting results are soon to come!
Just wondering if anyone knows what type of LED arrangement they use in those new commercial LED projectors like the Toshiba TDP FF1? They seem to indicate it's some kind of RGB LED if I'm not mistaken. Would there be any benefit to using an RGB LED grid with a controller to match the video feed (to match luminance behind the LCD, not produce pixels)?
throwit - I have a lense. It's a short throw NEC projection lense. I've gotten a dim image on the wall about 10 feet from the lense just by holding a normal gameboy behind it. The focal point of the lense is very short (22mm) so a larger LCD is out because even the 1.x inch gameboy screen goes blurry around the edges. I'm hoping I can fix this after making the projector housing by using the three adjustment rings on the lense. Anyone know what each ring is for? The thing came with no documentation and it's hard to adjust while holding all the components perfectly still. Exciting results are soon to come!
Lumens generally represent a sum of all the light emitted by a device. Since you cannot really integrate, you approximate it with just 9 measurements in ANSI method. The luxmeter is kept flush to the surface you do this integral sum (screen in this case). The luxmeter at its turn measures a flux itself, since its sensor is not a point but a patch, a small area.
As for the leds yes, the idea is to drive them in current, not voltage. However I read some leds are somewhat able to support the torture of being run without a safety resistor: http://led.linear1.org/myth-of-the-5-volt-led/
I guess the mobile led projectors use 3 leds only, looking at their fluxes. The 3 models available now are all DLP. Reducing led output could be used just like some home cinema projectors make use of a diaphragm to get >5000:1 contrast ratios. That gives well in specifications. It won't help the contrast inside a frame, though.
As for the leds yes, the idea is to drive them in current, not voltage. However I read some leds are somewhat able to support the torture of being run without a safety resistor: http://led.linear1.org/myth-of-the-5-volt-led/
I guess the mobile led projectors use 3 leds only, looking at their fluxes. The 3 models available now are all DLP. Reducing led output could be used just like some home cinema projectors make use of a diaphragm to get >5000:1 contrast ratios. That gives well in specifications. It won't help the contrast inside a frame, though.
DLP vrs color LCD
It would be much easier to get a decent image using LEDs if your color modulator was a DLP and color wheel, or even a DLP with red, green, and blue LEDs pulsed to simulate color wheel timing. Color LCDs just have an enormous amount of loss because 2/3 of the incident light is lost to the color filters, losses in the polarizers, the LCD geometry, etc.
Most commercial LCD projectors seperate the white light into red, green, and blue beams using a highly-efficient dichroic prism beam splitter. Then they recycle the part of each beam that has the wrong polarity and twist it to the correct polarity. Then they modulate its polarity using individual monochrome LCDs (no filters). Then they absorb the twisted parts of each beam with seperate polarized filters. The net result is MUCH higher efficiency than you can get with a color LCD, and all the heat is generated in the seperate polarized filters so the LCDs do not get hot.
So if you want to build an LED-based projector that is competitive with MH lamp-based projectors, I think you will need to experiment with better options than a color LCD. I have been thinking about building my own experimental projector using three monochrome LCDs driven by individual low-wattage red, green, and blue MH lamps. Should work with color LED arrays, although that would cost a lot more and have half the operating efficiency of MH.
It would be much easier to get a decent image using LEDs if your color modulator was a DLP and color wheel, or even a DLP with red, green, and blue LEDs pulsed to simulate color wheel timing. Color LCDs just have an enormous amount of loss because 2/3 of the incident light is lost to the color filters, losses in the polarizers, the LCD geometry, etc.
Most commercial LCD projectors seperate the white light into red, green, and blue beams using a highly-efficient dichroic prism beam splitter. Then they recycle the part of each beam that has the wrong polarity and twist it to the correct polarity. Then they modulate its polarity using individual monochrome LCDs (no filters). Then they absorb the twisted parts of each beam with seperate polarized filters. The net result is MUCH higher efficiency than you can get with a color LCD, and all the heat is generated in the seperate polarized filters so the LCDs do not get hot.
So if you want to build an LED-based projector that is competitive with MH lamp-based projectors, I think you will need to experiment with better options than a color LCD. I have been thinking about building my own experimental projector using three monochrome LCDs driven by individual low-wattage red, green, and blue MH lamps. Should work with color LED arrays, although that would cost a lot more and have half the operating efficiency of MH.
diy rgb led lcd
I've managed to get about twice the brightness by using 2 lenses and overlapping their images. It sure made a nice difference.
With 3 lenses I could project 3 areas of the same monochrome LCD, each backlighted by R, G and respectively B leds. Thus I'd have roughly 9x more light.
I don't know if I can get a cheap monochrome LCD, though. Without the printed colour surface they should come close to commercial 3LCDs in transparency. Not sure if they use the highly efficient polariser film, although some newer 17" units use almost half the power of the older units (led backlights?).
I've managed to get about twice the brightness by using 2 lenses and overlapping their images. It sure made a nice difference.
With 3 lenses I could project 3 areas of the same monochrome LCD, each backlighted by R, G and respectively B leds. Thus I'd have roughly 9x more light.
I don't know if I can get a cheap monochrome LCD, though. Without the printed colour surface they should come close to commercial 3LCDs in transparency. Not sure if they use the highly efficient polariser film, although some newer 17" units use almost half the power of the older units (led backlights?).
Hi,
zzonbi,
I've also found it fairly impossible to find the monochrome LCD panels for repairing projectors. This is especially true in the UK.
You can find certain panels like Sony ones in a few places, but then you'd need all the drive electronics to go with in (not simple, unless you're using a commercial projector). An example of the part number would be the LCX016AL or LCX016AM SVGA panel.....
http://www.horizontechnology.com/Sony_lcd_LCX016AL_6918.htm
The problem is driving these types of panel as they don't have simple video inputs?
Ok, changing the subject slightly.... I've done a few tests with these Jumbo LEDs but was hoping someone on here could suggest a way of collimating the beam better. Would a simple positive lens work quite well for "collecting" the LED light? Has anyone tried something similar? Actually, as I'm trying this with a DLP projector, I should be better off with a focusing lens, but I wouldn't know what to look for?
Guy Grotke, are you sure about LEDs having half the efficiency of MH lamps in terms of actual light output? It's just that I've been checking out the specs for MH lamps, and there seems to be a common misconception that they give out tens of thousands of lumens, but this only true of the total light output and AFAIK only a fraction of this light is collected by the reflector? btw, do you know if the more modern polarizer films can actually "collect" most of the light on the opposite polarizations like people say they do, or can polarizers only ever block the light on the other polarizations?
I've seen lumens specs for MH lamps of around 15'000 lumens or higher, but surely it can't be giving anywhere near that output out of the front of the reflector? Does anyone know more about this? I'm still a bit fuzzy on the actual lumens output of your average projection lamp (useful light into the PJs light path)?
Thanks for the info on series / parallel LEDs btw. I'm fine with the digital side of electronics, but I'm still getting to grips with analog theory.
zzonbi,
I've also found it fairly impossible to find the monochrome LCD panels for repairing projectors. This is especially true in the UK.
You can find certain panels like Sony ones in a few places, but then you'd need all the drive electronics to go with in (not simple, unless you're using a commercial projector). An example of the part number would be the LCX016AL or LCX016AM SVGA panel.....
http://www.horizontechnology.com/Sony_lcd_LCX016AL_6918.htm
The problem is driving these types of panel as they don't have simple video inputs?
Ok, changing the subject slightly.... I've done a few tests with these Jumbo LEDs but was hoping someone on here could suggest a way of collimating the beam better. Would a simple positive lens work quite well for "collecting" the LED light? Has anyone tried something similar? Actually, as I'm trying this with a DLP projector, I should be better off with a focusing lens, but I wouldn't know what to look for?
Guy Grotke, are you sure about LEDs having half the efficiency of MH lamps in terms of actual light output? It's just that I've been checking out the specs for MH lamps, and there seems to be a common misconception that they give out tens of thousands of lumens, but this only true of the total light output and AFAIK only a fraction of this light is collected by the reflector? btw, do you know if the more modern polarizer films can actually "collect" most of the light on the opposite polarizations like people say they do, or can polarizers only ever block the light on the other polarizations?
I've seen lumens specs for MH lamps of around 15'000 lumens or higher, but surely it can't be giving anywhere near that output out of the front of the reflector? Does anyone know more about this? I'm still a bit fuzzy on the actual lumens output of your average projection lamp (useful light into the PJs light path)?
Thanks for the info on series / parallel LEDs btw. I'm fine with the digital side of electronics, but I'm still getting to grips with analog theory.
I was hoping I could remove the colour layer of an old 15" LCD, but no chance. It's on the inside of the glass sheet not holding the TFT substrate. Perhaps exposing it to some destructive radiation 😉
I would try any positive lens placed so that its distances to leds and dlp are conjugates. Their ratio should match the led/dlp sizes one. With more leds each ought be beamed individually.
As for collector efficiency, looks like roughly half the light is lost (from the pdf I linked here). The better polarizers are said to improve flux 1.5x. It's an ingenious system which splits light according to its polarisation plane, and only twists the half which needs it, in a single pass.
The pdf explains the factors pending the collecting efficiency. Mostly arc length (smaller better) and necessary etendue at the LCD/DLP (higher better). A larger display, with larger viewing angles, needs less collimated light.
I would try any positive lens placed so that its distances to leds and dlp are conjugates. Their ratio should match the led/dlp sizes one. With more leds each ought be beamed individually.
As for collector efficiency, looks like roughly half the light is lost (from the pdf I linked here). The better polarizers are said to improve flux 1.5x. It's an ingenious system which splits light according to its polarisation plane, and only twists the half which needs it, in a single pass.
The pdf explains the factors pending the collecting efficiency. Mostly arc length (smaller better) and necessary etendue at the LCD/DLP (higher better). A larger display, with larger viewing angles, needs less collimated light.
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