rodger@hpdml93.HP.COM (Rodger Anderson) (09/22/88)
>/ hpdml93:sci.electronics / aardvark@nmtsun.nmt.edu (Bill Gallagher) / 9:34 am Sep 19, 1988 / >I'm looking for a source for Blue LEDs. I recall a discussion >last year that proved such a thing exists, but didn't save the >address where they could be bought. Now I have a good use for >them, and need alot of them. MAIL me the address if you know >it, but pointers to reputable, well-stocked supply houses would >be appreciated, too. I remember reading about them in the latest Radio-Electronics. I will have to recheck to get more exact information, but this might get you started. >Thanks for your help. >-- >Bill Gallagher aardvark@nmt.edu >NMT Computer Center "What's that watermelon doing here?" >Socorro, NM 87801 Drop bomb here--->[34 03'58"N/106 54'12"W] >---------- -- Rodger Anderson (rodger@hpdml93)
rsd@sei.cmu.edu (Richard S D'Ippolito) (09/24/88)
Chris, sit down and grab some coffee, and lighten up -- I'm going to yank your chain a bit later: In article <871@ritcv.UUCP> Christopher E. Piggott writes: >Hmm ... The reason I thought they would be effecient (since I guess I am the >one who started it) is because I read that GREEN LED's are less effecient >than red ones are, significantly. (I learned a neat lesson this week - if >you're not sure, SHUT UP ... some advice from me to myself). Sometimes, even when you're sure, it's still wrong! Read on, please... >Question: why are R.G.B. monitors Red, GREEN, blue, when GREEN is not one of >the primary colors (being a combination of blue and yellow)? Why shouldn't >it be red, YELLOW, blue? Green IS one of the primaries. There are two sets of primaries, (corresponding to the two ways of combining or processing colors), the additive and subtractive. Most of us are familiar with the subtractive set from coloring in kindergarten, even though the teachers never told us the correct names for the colors (art teachers generally know). Subtractive pigments or dyes work by absorbing (or filtering) certain wavelengths from incident or transmitted light and reflecting or passing the rest. When you put red crayon on white paper, the pigment subtracts most of the colors from the white light and reflects or transmits (depending on the thickness of the layer) the red. The primaries used in color printing and photograpy are really non-spectral, i.e., they are rather broad bands of wavelengths (some discontinuous) and are called magenta, yellow, and cyan. In fact, they are also known by the wavelength bands (colors) missing as minus green, minus blue, and minus red. When all are applied to paper, the result is black (although due to the imperfect nature of the dyes, real black ink is added to get a true and denser black. This is known as four-color printing, although black is not strictly a color. The additive primaries are red, green, and blue. All of them together produce white light (remember, all of the subtractive primaries yield black, or no light). These are the ones used in color TVs. These colors are spectral, i.e., can be produced from narrow bands of radiation. It is your eye/brain that "sees" white when stimulated by only three narrow frequency bands of light. True "white" can be obtained this way or by including all visible frequencies in the correct balance. >Projection televisions work the same way ... is it possible to emit green, >and blue 180 degrees out of phase with the blue component of the green, to >cancel out the blue and the green and make yellow? If not, how do you make >yellow? Now you can see that you "make" yellow by using only the red and green components. (If red, green, and blue make white and blue is minus yellow, then red + green = yellow.) Prove it to yourself -- turn off or block the blue beam. If you can obtain a magenta (minus-green) filter, look at your RGB monitor with only the green signal present. You will see (nearly) nothing. Phase means nothing here, as the radiation is not coherent. I suggest getting one of the Kodak photography manuals where they describe the four-color printing process. Also, for the true printing primaries, check the hidden parts of the box flaps on packaged foods; the test bars are sometimes visible. You will then see what magenta (erroneously called pink), yellow, and cyan (erroneously called blue or bluish-green) look like. I also invite you to explore chromaticity diagrams -- sometimes you can find them printed in color and with color phosphors plotted. >Thanks, everyone; sorry about the gum-flapping, I'll know better next time. I hope so! Now, don't EVER call green a combination of yellow and blue, O.K.? Cheers, Rich