Are you interested in LED light?

[tvrgeek]

Originally Posted by freax

Thats actually quite true, the MP3 codec leaves quite a few high frequency artifacts around ready and waiting to pop/damage our kids ears.

A study I read said the real culprit could be ear buds that seal. The evidence is they can cause damage at levels that you think are safe.

I too hate PWM dimmers. I much prefer multiple lamps. But only with incandescent can you change the color when you dim. LED's don't change color. Maybe someday we will have complex multi-color LED's processor control. Then we can simulate what a 1$ old fashioned bulb can do.

Another way to look at this subject was a calculation I read that China has the LED bulb manufacturing capacity to save the equivalent to three and a half 3-gorges dam output.

[jitter]

Originally Posted by tvrgeek

LED's don't change color. Maybe someday we will have complex multi-color LED's processor control. Then we can simulate what a 1$ old fashioned bulb can do.

Not someday, they're here now.

[tvrgeek]

Wow. I'll look for one and see what they charge. Generic 600L bulbs I have seen down to $16, so the anti is not so bad.

[5th element]

Cree, in there complete fixtures already use LEDs of different colours to easily tailor the end product CCT. They could easily configure the drivers to increase the ratio of red at lower power outputs to facilitate this, but I wonder if it's really worth it.

[Pano]

Originally Posted by AR2

Than scientific expression of the daylight is 5500K, specifying summer day at 2PM measured. Prepress or print standard is 5000 K. 6500 K really did not exist as a standard, but with age of computers started being introduced, simply because many monitors could not display lower color temperatures without dimming - lowering its output.

Yeah, when I worked in the fine art print biz we used special 5000 K lights for proofing. I'm not certain about the D65 for video (don't have the documents at hand) but Joe Kane told me it was adopted for color TV because the early CRTs needed all the help they could get. They should have been at D55, but where allowed to go a little blue for the brightness boost. I'll check SMPTE to see if it's a standard there.

Last year I put a ribbon of white LEDs under the kitchen cabinets. I love them! Very even, because it's so many LEDs spread over the whole length. The are underneath and out of view, they just light the counters and back-splash. Really nice at night for those 2AM refrigerator raids.

Doing light bright enough to work by would take a lot of LEDs, but it sure would look nice.

[SY]

Originally Posted by AR2

Than scientific expression of the daylight is 5500K, specifying summer day at 2PM measured.

In Texas, that was the air temperature.

[blizzardbuffalo]

Originally Posted by jitter

Not someday, they're here now.

To add to this, there is also a Kickstarter for a new LED bulb called LifX going on at the moment (seems to have sold out) which looks pretty good and comes in bayonet, Eddison screw and downlight types. They were originally going to come in Master/Slave config but that appears to have changed to all bulbs being a gateway. They have a tech blog here for those that are interested.

Phillips has something similar called the Hue that was recently released but it is slightly more expensive and only available through apple stores.

I ordered a 4 pack of the LifX for lamps and such around the house, The demo video looks like it has a decent amount of light, but I am not quite sure they throw enough light to be the sole source of light in a room. That said, it is just a demo, maybe the final product will be better. Hopefully they won't take too long to deliver, they estimate March 2013 but it is Kickstarter...

I mostly use Halogen downlights in my home, they simply light up the rooms of my house better than anything else I seen. I have tried LED downlights, and quite simply they were rubbish. I didn't have them in long enough to see if I saved power or not, but they only lit up the space directly under them, which is quite frankly completely useless.

[AndrewT]

If I ran a group of different coloured LEDs in parallel, could I get a reasonable approximation of white light?

Would that group, with each diode optimised for it's colour emission, be more efficient than using a group of white LEDs where the manufacturer is converting Blue emission into the missing colours?

Could the CRI of the mixed colour group be better, or even much better, than a white light LED? Presumably the ratios of currents to the individual colours could be moved around to find a white light colour that the user/operator likes, or thinks appropriate.

Finally, what are the minimum number of colours required to give a good CRI index? All six of red, orange, yellow, green, blue, purple. Or could a few be omitted and still achieve a good CRI and high efficiency?

[jitter]

Some of your questions might be answered by this article. It's a year old, but should still be valid (improvements in LED world are still going at a brisk pace).

[tvrgeek]

Lots of good thought here. Let's hit a few basics:
* We see only three narrow bands of color. This is why using three phosphors seems to give us the equivalent of white light. (TV tubes, florescent tubes, etc).
* If you don't produce all the colors in between, you save energy.
* Most lights produce more non-visible infra red than visible.
* Lighting is based on the equivalent emission of a hot wire (incandescent bulb)
* Color is based on the temperature of that wire in a vacuum.
* Within the visible spectrum, we see only 32% of the emitted light.
* The current LED's, either filtered blue of florescent dye IR, are about the same efficiency as a CFL. About 18%.
* Optimizing LED frequency emissions is the trick. This is a quantum physics problem. You can't just pick any old wavelength. You can Google LED colors to see what has been achieved so far.
* LED's output degrades with time. The LED does, and if a phosphor conversion type, so does the phosphor. I think the spec on a Florescent is 60%. LED's last quite a bit longer but do "wear out" and need replacement before total failure.
* As you get older, you need a lot more light to see the same level of detail. Where a single 8W LED may be fine for a kid's bedroom general illumination, it is no longer enough for me.
* LED's have an advantage for bulbs that need to flash. Filaments don't like going from cold to hot. If you want to keep flashing incandescent lasting a long time, only turn them off to a dull orange.

So, where does that leave us? IF you could have three LED's that produced the exact correct three colors to match our eyes and regulate them at the exact proportion, then yes, what looks like white is possible. What temperature would be a question. You can buy such a thing from pro photography suppliers for $800 and up for a one foot square fixture. Another way to get this is called an LED TV set. Color filters over white LED's.

What I don't know is how exact our color perception person to person is. Might be fun to google. Note that the phosphors in TV's are famous for not producing "mustard" correctly and that many color-wheel TV sets went to 4 or 5 filters to improve the colors. Was that because of the inability to built stable filters of the correct color? Don't know. If you built a bulb with several LED's of different colors, you would need control systems for each. Rather expensive for a small bulb. They do this for pro-photography, and someday when we can build cheap LED's on roll to roll process so we cover out entire ceiling, maybe it will make sense to do so. (Never saw a desk light on Star Trek did you)

LED's send light in one basic direction. This is great for down-lighting as you don't need reflectors and waste energy illuminating the fixture. If you look at the replacement T8 lamps, their total Ls are about half a standard tube, but the light measured on a surface 8 feet away is the same. So, 50% savings just from how they work. On the other hand, if you have an LED in a table lamp with a shade to give general lighting, you have no savings from directional feature, so the LED is about the same efficiency as a CFL.

I like my little LED in-cabinet lights I use to Illuminati some Binko glass. Almost as good as Halogen does for making glass pop, but way less power and heat inside a cabinet. I have 6 700L A base bulbs in one of those tacky chrome bathroom fixtures to give bright light in a bedroom. Ugly, but very nice light and when I had 3600W of incandescent, the AC could not keep up. I use LED for a reading light in that room as the bulb is a foot above my head and the heat from even a CFL was too much, never mind the buzz. I have a small outdoor LED bulb as I need very little light, and it has to work when cold. I love the LED down floods PAR36 size in my kitchen. Because they have half the heat of the CFL's, and half that again from the original, I can actually insulate completely the top-hat ceiling cans and never get hot. Safety and no longer have 5 light bulb powered room exhaust fans in my ceiling.

Dirty little secret: The best way to get the most energy efficient light is to put the light where you need it. For general illumination, a single exposed bulb in the center of a white ceiling saves a lot more power that indirect lighting fixtures. As I look up, I have two 32 W CFL's behind a very low trans-missive stained "Tiffany " style ceiling fixture reflecting against an off-white ceiling. If I pulled it down and put in a $2 utility fixture, then painted the ceiling bright white, I could use a 8W LED and have more light. If I did not have a dark floor, wall of dark bookcases, and dark gold walls, it could be even brighter. It would just not be as comfortable an office. What this means is we are still so rich as a culture, we can afford to waste 3/4 of our lighting energy budget. In many places in the world, having a 1W LED ceiling lamp would be a major life enhancement. (They don't have 100W class A amps either)

Of course, my Garage is painted bright white. I am going to paint the floor too as I am convinced concrete has the magic ability to suck light waves from thin air.

*Depending on the control circuit, an LED brake light comes on far faster than an incandescent. Believe it or not, those few milliseconds do have a measurable advantage in reducing rear end collisions. If I remember the report, it was about two feet of breaking distance. Another great place is you can replace your Volvo 240 tail lights with bright LED's and not melt the lenses as they are so prone to do. You don't get the speed advantage from white bulbs and the florescent conversion types fade out just like CFL's do. If you have a "cave black" room, try it out to see how long they glow.

Enough of than. Need more coffee. Time to open the blinds and get free light.