| Electronics > Beginners |
| Match LED Brightness |
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| tooki:
--- Quote from: Kasper on November 06, 2019, 01:05:46 am --- --- Quote from: tooki on November 05, 2019, 06:28:37 pm --- --- Quote from: Kasper on November 05, 2019, 04:55:37 pm --- --- Quote from: tooki on November 05, 2019, 10:20:14 am ---If you're starting by selecting two LEDs with similar rated output at the same current, as you did, then yeah, current tells you something. --- End quote --- Before accusing me of cherry picking my data, you should look at their site. Relying on such a big assumption just shows you don't have a good argument. --- End quote --- :-DD Bro, you lost the disagreement long ago. You made a claim that is readily disproven, and multiple people have done just that. You’re just making yourself look silly by digging in your heels on something that is so easily disproven. Anyhow, I didn’t say you cherry picked your data. You selected LEDs with broadly similar light output. How that came to be is irrelevant. You chose randomly and so did I when I literally grabbed the closest catalog at hand. But the upshot is, your claim that LEDs of similar current will have similar brightness is plain and simply not true. --- End quote --- Once again you prove you have no good argument by choosing fallacies over details. --- End quote --- Your claim has been completely disproven, end of story. No fallacies, no cherry picking. Your stubbornness is astounding, given that it’s literally trivial to disprove your claim. One 20mA LED with 3mcd, another 20mA LED with 14,000mcd. Not even in the same ballpark of brightness. |
| james_s:
Buy some samples of the LEDs you wish to use, then experiment with variable resistors to get the brightness you want. Measure the resistance of the pots then and select fixed resistors of similar value. This is waaay easier than trying to calculate from the datasheets and will give better results anyway. You're always going to need a different resistor value for each color, the forward voltage for example of a red LED is usually around half that of a blue LED. |
| kripton2035:
a device like this one may help too. http://www.neufeld.newton.ks.us/electronics/?p=1145 |
| Kasper:
--- Quote from: tooki on November 06, 2019, 07:31:48 pm --- --- Quote from: Kasper on November 06, 2019, 01:05:46 am --- --- Quote from: tooki on November 05, 2019, 06:28:37 pm --- --- Quote from: Kasper on November 05, 2019, 04:55:37 pm --- --- Quote from: tooki on November 05, 2019, 10:20:14 am ---If you're starting by selecting two LEDs with similar rated output at the same current, as you did, then yeah, current tells you something. --- End quote --- Before accusing me of cherry picking my data, you should look at their site. Relying on such a big assumption just shows you don't have a good argument. --- End quote --- :-DD Bro, you lost the disagreement long ago. You made a claim that is readily disproven, and multiple people have done just that. You’re just making yourself look silly by digging in your heels on something that is so easily disproven. Anyhow, I didn’t say you cherry picked your data. You selected LEDs with broadly similar light output. How that came to be is irrelevant. You chose randomly and so did I when I literally grabbed the closest catalog at hand. But the upshot is, your claim that LEDs of similar current will have similar brightness is plain and simply not true. --- End quote --- Once again you prove you have no good argument by choosing fallacies over details. --- End quote --- Your claim has been completely disproven, end of story. No fallacies, no cherry picking. Your stubbornness is astounding, given that it’s literally trivial to disprove your claim. One 20mA LED with 3mcd, another 20mA LED with 14,000mcd. Not even in the same ballpark of brightness. --- End quote --- I counted 6 fallacies in your last post, 7 if you count the values without links or even part numbers. I use evidence and you use fallacies. It does not look like I am wrong. If I am, please give explanation instead of spewing fallacies. I gave you a chance and dug through JLC library to learn more and I learned you were wrong. I shared my findings, you replied with nothing but fallacies. You finally tried to share some evidence though without part numbers it really is just another fallacy. I gave you another chance and looked on digikey and once again I find that you are exaggerating. Digikey.ca search: LED - discrete, smt, in stock, 20mA, blue and yellow. Min intensity: 3.2 mcd. Max intensity: 5700 mcd That is huge range, still smaller than your numbers because you exaggerate too much. Odds of someone ordering 1 on either side of that range are slim. Odds are they will pick identical packages and similar costs. If the search is narrowed by package: 0603: 6 mcd - 1600 mcd 0805: 4 mcd - 1990 mcd Still a large range but odds of purchaser choosing one on either end of that spectrum are slim. If they choose cheapest LEDs or most in stock, the range is significantly reduced. Cheapest 10 in package 0603, cut tape: intensity: 63 mcd - 170 mcd viewing angles: 120° - 140° (2/10 not listed) Highest stock 10 in package 0603, cut tape: intensity: 104 mcd - 800 mcd (8/10 are between 104 mcd and 180 mcd) viewing angles: 60° - 130° (8/10 are between 120° and 130°) This helps explain why I found such a limited range of intensities and viewing angles when I looked on the library in question, JLC's library. If you must continue, please give evidence instead of fallacies. |
| Zero999:
Of course simply selecting the same forward current doesn't give equal brightness for two different colour LEDs, even if differences in beam angle are taken into account. Implying that it's a good rule of thumb, is just not true. As mentioned above, the radiometric efficiency depends on the chemistry and the luminous efficacy, depends on the sensitivity of the human eye to the light being produced. A classic example is a royal blue vs modern, high efficiency emerald green LED. The royal blue LED will have a better radiometric efficiency i.e. optical power out, in the visible spectrum vs electrical power in, but the emerald green LED will look brighter and have a higher luminous efficacy because the human eye is much more sensitive to that colour. It will also depend on whether the observer's eyes are dark adapted or not. In low light conditions, the peak sensitivity of the human eye shifts to shorter wavelengths, which will suppress reds and accentuate blues. In bright daylight, the reverse happens. Going back to the original post, it might not even be desirable to have all colours equal brightness, because it will probably look unnatural. The blue and red LEDs will look much brighter than they should be and the green and yellow LEDs much dimmer. It might make more sense to make each LED emit the same optical power, or scale the optical power output, to the expected black body spectrum of an object at a certain temperature. https://en.wikipedia.org/wiki/Black-body_radiation#Spectrum https://upload.wikimedia.org/wikipedia/commons/1/19/Black_body.svg |
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