Uploads from kriegsman, tagged color

Accidental "blue-green shirt day"

nobody@flickr.com (kriegsman) — Thu, 03 May 2012 07:35:45 -0700

kriegsman posted a photo:

Mollydome

nobody@flickr.com (kriegsman) — Tue, 06 Sep 2011 10:50:12 -0700

kriegsman posted a photo:

(as shot)

Purple LED lights! (or are they?)

nobody@flickr.com (kriegsman) — Thu, 11 Dec 2008 05:43:45 -0800

kriegsman posted a photo:

I'd wanted them for a couple of years, and finally I found a local source for PURPLE LED fairy (faerie? feri?? no.) lights, and hooboy was I happy! Yay! Purple LED lights, no shipping! As soon as I got home I strung them up.

But- wait! I know one or two things about semiconductor physics and engineering -- and there's NO SUCH THING as a purple LED! What's going on?!

Purple LED lights: actually made from red + blue LEDs!

nobody@flickr.com (kriegsman) — Thu, 11 Dec 2008 05:43:29 -0800

kriegsman posted a photo:

Purple LED lights seen in room light, but this time with the viewer's eyes (and camera) moving quickly past them. Instead of steady streaks of purple light, you can now see that each bulb has a steady red LED glowing in it, and also a blue LED that is only on about three-quarters of the time.

And apparently, 100% red LED glow plus 75% blue LED glow equals this color of purple!

Purple LED lights, apparently...

nobody@flickr.com (kriegsman) — Thu, 11 Dec 2008 05:43:35 -0800

kriegsman posted a photo:

Purple LED lights as seen in room light, with the eyes (and camera) held steady. But are there REALLY purple LEDs in there?

Purple LED lights: How they work.

nobody@flickr.com (kriegsman) — Thu, 11 Dec 2008 05:43:22 -0800

kriegsman posted a photo:

There really is no such thing as a single LED that glows purple. To make purple LED lights, they make each bulb with one red LED and one blue LED inside it.

But if both LEDs were fully on all the time, the color would be too "blue", and not "purple" enough. (Blue LEDs are brighter than red ones, and they'd outshine the red ones and make the mix look too indigoish.)

And LEDs cannot really be "dimmed"; either they're on full blast or they're off.

So to mix just the right color purple, each tiny bulb keeps its red LED on all the time (100%), but then it pulses the blue LED on and off and on and off, so that overall it's only lit a fraction of the time, and thus appears dimmer. After all, if its only on half of the time, it's only putting out half of the light in a given period of time.

If the flashing of the blue is fast enough -- faster than the steady eye can see -- you don't even notice.

BUT! If you move your eyes or your head (or your camera) quickly past the bulbs, the secret of the on-off-on-off blue LEDs is revealed!

You could even just take a ruler and measure the length of the bright blue "on" streaks compared to the red parts on this picture, and figure out the exact proportion of red and blue that the manufacturer mixed to make this color of purple.

Science. It works, _.