[Joel] has a very specific color temperature of lighting he wants in his home. So specific, he’s decided to build his own LED lighting to get it. Actually, he’s still searching for that perfect shade of white, but doing so has learned a lot. He initially made some very pretty PCBs, but then found that hand soldering them made quite a mess. What better time to delve into reflowing? He shares his positive initiation to the skillet method in his latest update. The search still continues for that nice warm glow he’s desiring. We’ve actually seen [Joel] before, he likes smoked meat.
Think his site is, uh, hackaday-ed?
I have had switching to LED lighting in the back of my head for ages… It will be interesting to see what finally happens with this.
http://74.125.95.132/search?q=cache:rKMGgYmvNKcJ:jmillerid.com/wordpress/2010/03/led-lighting-part-1/+http://jmillerid.com/wordpress/2010/03/led-lighting-part-1/&cd=1&hl=en&ct=clnk&gl=us&client=firefox-a
@Bhima, same here, fed up with the CFL’s I have taking an age to get to full brightness, and I want a remote control system so I can adjust on/off/brightness without having to get up :)
Don’t forget, [Joel] likes mustaches too.
My other half did a research project on the metamerism of candlelight using LEDs, including full specroradiometer measurement and a whole heap of real-world testing by getting people to colour match. It threw up and highlighted quite a few interesting points, such as how differently everyone sees the same light source, how people may match the light source perfectly in their view but it be completely off to the next person, and how the reflected light from the LED source is totally different to the original light source even if the LED source closely matches the original due to the rather narrow output ranges of coloured LEDs and the tendency to blue in white LEDs. I’ll see if she would like to post the link.
I was gonna post this on the guy’s page, but its down, so ill post here as I wrote this already.
A little on lighting theory…
Single color (non-white) LEDs emit very narrow wavelengths of light. While it is true that mixing the primary bands of color, red blue and green, will produce ‘white’ light in theory, it will be lacking in a majority of wavelengths that would otherwise be found in true white light or sunlight. What this means practically, is that the quality of light will not make an object’s color ‘pop’ unless it falls in one of these narrow bands. So, mixing amber light from red and green LEDs will make amber objects look muddy, while an amber LED will make an amber object vibrant. Now you are using while LEDs, and that will fill the spectrum nicely, but your red green and blue LEDs will just cause ‘spikes’ at their respective wavelengths. Here is a graph of the RebelColor LEDs by wavelength ( http://imgur.com/ckfhv.png ). You can see the major gaps between colors even when there are all 7 colors, so using just three makes this more pronounced. If you really want to mix a nice color of white, you are better off mixing different color temperatures of white LEDs. As you can see in these two images ( http://imgur.com/HVvby.png and http://imgur.com/S1rYQ.png ), White LEDs have a broader and softer curve, albeit irregular with the spike in the blue band. Perhaps mixing various color temperatures of white could give you a more palatable quality of light. If you line up the three graphs, the two white and the 7 colors, you will see the valleys in white that you may want to fill with other color LEDs. That being said, Incandescent light, no matter how energy inefficient, will always produce a warmer, more visually pleasurable quality of light.
@james please do post link! I am interested.
His Flickr photostream for this project seems to be of more use than his actual site.
http://www.flickr.com/photos/jmillerid/4420218032/in/photostream/
And I particularly love the “Reflow Skillet” concept.
http://farm5.static.flickr.com/4003/4433241531_2a5254c079_b.jpg
Sorry for the downed web site today… stupid hosting service. My Flickr set has the pictures at least…
@james yeah definitely post a link!
My next step will be to try individually adjusting R G and B LEDs to try to “roll my own” white. In using the “2700k white” LEDs I noticed that the color in the middle of the radiant pattern was much pinker than the edges, so I’m also going to try reflecting/diffusing the pattern together to try to blend it a little.
Reflow skillet was AWESOME… no other way to do surface-mount components IMO.
@xeracy – Thanks for the great info, that will help a lot!
ps- site is back up
Just the right color temperature? Try “pretention” it is a soft shade of blue/red. Sometimes can be found in cafes and breweries. So glad I got out of the home entertainment/ automation biz. It is amazing what clients will waste your time on/not pay for.
Hi guys, here it is – I’ve not had chance to ask her but I’m sure she’ll be happy for all to see it. I’m sure she’d be pleased to hear some constructive comments too, especially as it was her first delving into microcontrollers and digi electronics.
http://lightingupshakespeare.wordpress.com/
The site was a bit of publicity of her work with a non-tech audience, rather than a how-to or an in-depth report, so she has left out a lot of the detailed steps and pages and pages of data collected!
Nice, but why not use PWM to blend a few colors by software? :|
LEDs have no color temperature. Color temperature is a property of blackbody radiation as exemplified by incandescent light. LEDs and flourescents and similar lamps do have a color temperature equivalent. This means that when illuminating a white object a source with a given color temperature equivalent will produce the same perception in a human being as when the white object is illuminated with a source with the corresponding color temperature. However, objects of other colors may not look the same.
there are several commercial options that allow you to tune in particular combinations of led sources. typically WW/CW but you can also fine WW/CW/A and RGB, RBGA, RGBAW, and RGBAWW
they can be spendy, but overall cheaper than buying accurately binned LEDs in the quantities you want for just a few fixtures.
(i used to work in lighting design, and have actually done parts costing on commercial fixtures to compare for my own DIY version. of course it’s less fun than doing it yourself….)