DIY Video Projector Part II

[ace3000_1]

Ok, I think I see where I got confused , mutiplying the candela by 12.57 seems to be a way to convert to lumens when your light source radiates sphericaly or something (or at least I think thats what they meant, still not sure really), where as leds only cast their light at a particular "viewing angle".

Playing with leds and thier brightness can be tricky, i personally dont fool with leds, Yet! but may do further down the line so realy i have no say on the matter, but what i did know is that 250lumens will never come from a 20000cmd led.

Parabolic reflected lamps are measured like leds aswell, anything with a beam wont be measured in lumens on a manufacturers site, why? not sure, but its to do with the beam angle and there is a way to convert it back.

Regarding light loss, there is a way we can tackle this without a great loss of light, but a few calculations need to be kept in mind, here is the thread where i posted the idea.

http://www.diyaudio.com/forums/showt...580#post459580


Trev

[elstcb]

My 2c:

A narrower beam may give a lower lumen output per LED but will probably produce less light loss (to the surroundings before the LCD) and give a much crisper picture.

I have yet to see anyone here do any decent pulsing with these white LED's, traditional LED's should take a couple of Amps if it's for a very short period of time giving a perceived increase in brightness. It would be great to find out how much current the cheap white LED's can take and if it made their colour better or worse.

verbose mustafa's calculations look spot on, great work with the dos program by the way.

[elstcb]

70,000:1 Contrast Ratio (pdf)

No idea how acurate their contrast ratio claim is but it's interesting to see how they've used an LED matrix as a backlight, not quite what we're discussing here but still kinda relevant IMHO.

[Guy Grotke]

Personally, I love the new super-bright white LEDs, but there are a few issues that are being ignored here.

1) LEDs are less efficient than MH lamps. That power consumed, but not converted to light, has to go somewhere. Where it goes is... heat! So an LED projector light source will actually get hotter than a same-lumen MH lamp light source. (The heat WILL be spread out more, but you will need more airflow to get it out of the box.) It will also cost you more to power it.

2) This is the killer: All the very bright whites I have seen use a narrow-band blue LED to stimulate a narrow-band yellow phosphor. When we see blue + yellow, the blue stimulates our eye's blue receptors, while the monochromatic yellow stimulates both our red and green receptors. So it looks "white" to us. But it does not look like an even mixture or red, green, and blue to the red, green, and blue filters on the LCD panel! The blue will get through fine, but reds & greens will be very dark. This is why LED projection tests go through the lenses just fine, but look horrible when you pass it through an LCD.

3) There are true RGB LEDs that are used for devices that need to create any color on demand, like paint matchers. But those LEDs are much more expensive and much too dim. The other option is to make your own array of R, G, & B LEDs. Then you would get each color you need, but you would also introduce lots of color artifacts in the image.

[Guy Grotke]

They get "70000:1 contrast ratio" by using a backlight made of individual pixel LEDs? But that leads to a more interesting question:

Once you have a full-sized panel of RGB LEDs,why would you put an LCD in front of it? Why not use the LEDs as the display device directly. You could run them at 10% of the power needed to get the same amount of light through LCD filters, etc.

[arniel]

Originally posted by Guy Grotke
They get "70000:1 contrast ratio" by using a backlight made of individual pixel LEDs? But that leads to a more interesting question:

Once you have a full-sized panel of RGB LEDs,why would you put an LCD in front of it? Why not use the LEDs as the display device directly. You could run them at 10% of the power needed to get the same amount of light through LCD filters, etc.

Size?
Speed?
Soldering?

[Guy Grotke]

>Size?
>Speed?
>Soldering?

My point was that the 70000:1 contrast ratio idea doesn't make much sense. If you have individual pixel backlights, why not just use those as the display device? I don't see what putting an LCD in front of them gets you.

Size: If you have individual pixel LED backlights, then that has to be exactly the same size as the LCD panel. (In fact, they would have to very precisely aligned.)

Speed: LEDs are thousands of times faster than LCD pixels.

Soldering: An LED array like this would have to be fabricated in a semiconductor processing facility, rather like where they make LCD panels. No soldering would be involved, just lots of photo-etching and vapor depositing using very nasty chemicals.

AND it doesn't help us at all, since it would result in a panel with a fixed backlight. Even if you could seperate the backlight from the LCD, the LCD would still be 400:1 max.

[mrmonopoly]

Hello all again , i have something which you lot will find very intresting. I have still been followig the project through , and a new LED device has just come into a local electronics store claming this new LED gives more light that a Halogen bulb and is priced at £8 each. Here are the details.

• Very high brightness
• Very high flux per LED
• Very long operating life (to 100k hours)
• Cool beam, safe to the touch
• Instant light (less than 100ns)
• Fully dimmable
• No UV Superior ESD protection
• More energy efficient than incandescent and most halogen lamps

Luxeon star hexagonal modules can be connected and powered in a close packed hexagonal configuration for tight spacing and increased light output per unit area. They are available in white, green, cyan, blue, royal blue, red and amber. Typical applications include passenger reading lights, portable lighting, orientation/emergency lighting, mini accent lighting, decorative lighting, fiber optic alternatives and other appliances. This range of products have a batwing (low dome) radiation pattern and slots in the aluminium-core PCB for M3 or #4 mounting screws. All codes have a viewing angle of 110°

if anyone has any views i be pleased to hear them

[mrmonopoly]

or there is this one , data sheets are avalible

Luxeon V Emitter Lambertian


• Highest flux per LED family in the world
• Very long operating life (up 100k hours)
• Available in white, green, cyan, blue, royal blue
• Lambertian radiation pattern
• More energy efficient than incandescent and most halogen lamps
• Low voltage
• DC operation
• Cool beam, safe to touch Instant light (less than 100nS)
• Fully dimmable
• No UV Superior ESD protection

Luxeon III is a revolutionary, energy efficient and ultra compact new light source, combining the lifetime and reliability advantages of LEDs with the brightness of conventional lighting.
Luxeon III is rated for up to 1000mA operation, delivering increased lumens per package.
Luxeon emitters give you total design freedom and unmatched brightness, creating a new world of light.

[elstcb]

Luxeons have been looked at several times in the past, the broad viewing angle they give might be good for the numbers but means you'd need a lens for every unit in order to get parallel light. They also tend to be more expensive per mcd than traditional LED's.