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| Deep Red vs High Efficiency Red in this datasheet? |
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| NiHaoMike:
--- Quote from: David Hess on December 20, 2018, 01:22:24 am ---Very old "high efficiency" red LEDs (GaP?) only had high efficiency at low currents but this made them suitable for low power circuits. --- End quote --- Modern green and blue LEDs also need surprisingly little current to get a visible glow. I modded a clock to have the backlight be always on at a very low level - something like a 100k resistor across the transistor that switches the blue LED backlight. The 1000mAh battery easily lasts months between charges. At some point, I stuck in a piece of fluorescent orange paper to act as a phosphor, to make the glow less harsh at night. |
| Zero999:
--- Quote from: alank2 on December 19, 2018, 07:26:16 pm ---It is odd. I do have all but the "deep red". I set them to a low current setting, around 10% of maximum: green "2963" is very nice her "2962" is close orange "2964" is decent yellow "2961" is much dimmer than the rest I wonder how the deep red would compare, but i don't have one. The goal is bright display with least current use... --- End quote --- LEDs are most efficient, in terms of power in vs radiant power output, in the red-orange and blue-violet ends of the spectrum. Green may seem brighter, but that's because it's near the peak response of the human eye. Yellow is very poor, so much so, a deep blue/violet/near-UV LED with a phosphor can give higher efficiency, than a yellow die, but the forward voltage is higher and it's much more expensive. Improving the efficiency of LEDs in the middle of the visible spectrum is still work in progress. Deep red will be dimmer than orange-red, mainly because the eye is less sensitive to it, although the radiant efficiency of LEDs also drops at longer wavelengths. Another reason why blue LEDs light so well at low currents, is because the human eye's peak response shifts to shorter wavelengths, at lower illumination levels. |
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