I need a high brightness LED in red and yellow in a T1 package. What mcd rating would be considered high? I need something that really gets some attention from about 10 feet but not obnoxious.
100 mcd or so? Higher or lower? Are they usually in a clear lens?I never paid any attention to it but what is a most common mcd for run of the mill led's? - thanks
If you want it to not be obnoxious get one with a diffused lens. The clear lenses allow the tiny die to be seen and all the light ends up on one rod/cone no matter the distance and so seems irritatingly bright. At least that what I see. LEDs are like stars, no discernible size.
It's actually amazing we can even see stars if you think about the incredible distance. I guess that's made up for by the incredible brightness! I understand there are certain types of objects (forget which ones, but they have something like a black hole in them) which spew mind boggling amounts of radiation from the poles reaching into the X-ray region. If they were anywhere at all nearby in our galaxy (and pointed toward us of course) they would render life on Earth impossible. In fact, much of the milky way is uninhabitable by humans because of extreme radiation. We are very lucky to have evolved in a backwater, safe from such terrors.
Quasar.
.
Well, where else could have humans evolved?
Anthropic Principle.
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Joe Gwinn
I ordered some red and yellow Kingbright both are 900 mcd. 40 cents. Clear lens but I'll get some diffused also. Hopefully 900 mcd should be what I'm after.
Huh? If it weren't for the extremely high radiation we could have evolved in many parts of the Milky Way, that's my point. The radiation did it!
I've never had much luck using mcd as a guide. I think mcd is a total emission over the entire sphere surrounding the LED (someone correct me if I'm wrong) so you also need to consider the angle of emission. With a diffused lens the light goes out at wide angles and from a larger surface, so the apparent brightness will be less.
I hope the radiation from your LEDs doesn't wipe out life on Earth. Maybe the diffused lens will be a good idea for all our sakes.
lumens it total light output, candelas is how concentrated the beam is.
I stand corrected. I don't work with this enough to remember. There's one or two other light measurements that I get mixed with with these as well.
The angle of emission still needs to be considered in an application. I guess what I was remembering is one that has a low angle will have a higher candela rating for a given total light output. Good for illuminating light pipes, but not so much as an indicator unless the person is standing in front of the LED. I see this issue even with PC keyboards. Press the Caps Lock button and the little dot is brightly illuminated, but when you release it the illumination goes way down because the light pipe is in the button and is now intercepting less light. It can be hard to tell if it is actually on or just lighted by diffused light from all the push buttons around it. Keyboards seem to leak tons of light around the keys which is not likely to be by accident. This computer has relatively little light coming through the key labels making the key very hard to read in any but the darkest environments. With the keys being silver (like the rest of the machine) the contrast goes to zero in normally lit rooms.
Stupid keyboards!
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