white light vs. blue light?

I am curious as to why my PT Attitude and Opalec produce such different color light.

Both use 3 LED's and the light appears to be equally bright, but the color of the light is very different.

The Attitude has a blue hot spot while the Opalec has a white hot spot, in fact, it's the whitest hot spot that I have ever seen in an LED.

What is the reason for this?

Is it because different LED's are used?

Is it because the Attitude is overdriven while the Opalec is not?

Any reasoning from the more knowledged would be appreciated.

i think it's due to the amt of phosphate in the LED
i will leave this to the experts to explain

There is no such thing as a "White LED", a LED is a monochromatic light source, it can only generate a light of a single color - as we know, "White" light - is a mixture of many colors

Our Sun, is a gigantic fusion reactor, converting 900 Million Tons of Hydrogen into 850 Million Tons of Helium every second - the 5 Million Tons left over, is made into light, heat, and other forms of energy

The White LED works in much the same way as a flourescent light bulb works, the Mercury vapor inside the tube has two lines of operation 275nm (Shortwave UV) and 365nm (Longwave UV) - as the electrons strike the side of the tube they excite the Phosphor on the side of the tube

As the Phosphor changes from a high energy state to a low energy state, a photon is released

Depending on the amount of energy that the electron raised the phosphor to, you get different colors - mostly random, and you get "White"

There are several different "colors" of white that are available in Flourescent tubes "Natural White" "Glow Bulb" "Black Light" and others, and they are just a different type of chemical for the phosphor coating on the walls of the tube

In the LED, the same process is happening, but instead of using Mercury Vapor (which is being used up in the process of the FL tube), they are using a BLUE LED (higher energy state) - the light output from the Blue LED - excites the Phosphor - and the same reaction occurs

Each company uses a different type of chemicals for its Phosphor, and as such - each company has a slightly different color spectrum on the white; and color temperature

Incandescent Light bulbs have been around for nearly a hundred years, and there have been great improvements in the technology of them

The original light bulbs had a vacuum inside instead of Argon, which caused them to "cloud up" the glass as the electrons struck the glass

White LEDs are fairly new, and I expect the same thing - over time, the chemical nature of the Phosphor will improve - and we will see higher Lumen/Watt output and better color rendition of "White"

Mike
www.inretech.com

i think you're confusing electrons with photons.

"tube has two lines of operation 275nm (Shortwave UV) and 365nm (Longwave UV) - as the electrons strike the side of the tube they excite the Phosphor on the side of the tube"

PHOTONS of UV are what cause the phosphors to fluoresce.

"The original light bulbs had a vacuum inside instead of Argon, which caused them to "cloud up" the glass as the electrons struck the glass"

No, no electrons are emitted in an incandescent (or fluorescent) bulb, incandescent bulbs cloud due to the tungsten evaporating off of the filament and being deposited on the inside (cooler) surface of the bulb.

Yes, you are correct about those facts

And in the Halogen bulb, the Halogen causes the tungsten to deposit back onto the filament

Its interesting to know that Tungsten was originally called "Wolfram" and still is on the table of elements as "W"

I just wanted to give some background on lighting technology and bring a point, that White LEDs are fairly new - and I am sure they will improve

Mike
www.inretech.com

Incandescent Light bulbs have been around for nearly a hundred years

124 actually! The first commercial electrical light bulb was produced by the Edison company in 1878,and used a carbonized bamboo filament.

Tungsten filaments arrived in the early 1910s. Coiled-filament tungsten bulbs came along at around the middle of that decade, and the basic design of the pear-shaped incandescent household bulbs we use today has not changed much since the 30s.

Originally posted by INRETECH:
...Each company uses a different type of chemicals for its Phosphor, and as such - each company has a slightly different color spectrum on the white; and color temperature....

Click to expand...

<font size="2" face="Verdana, Arial">Why so much variation from one LED to another within the same company?

Brightnorm

There is a lightbulb that has been burning for 100yrs

http://www.centennialbulb.org/

I assume this longevity to the low current

Mike
www.inretech.com

Brightnorm,

2 members provide 2 different answers, your question seems pointing out the correct one

Alan

Companies also sort their LED's into BINs.
Every LED is sorted by the other LED's with more or less the same color ('white').
Example Nichia: A-rank = blueish white
B-rank = 'neutral'white
C-rank = greenish white
D-rank = Incandescent white
You also have A1, A2, B1,....
Probably the Attitude has B1 ranks (white with a touch blue) and I know the Opalec has C-ranks!

Hope this helps...

There is a lightbulb that has been burning for 100yrs

http://www.centennialbulb.org/

I assume this longevity to the low current


I know that one well! They even have a BulbCam looking over it all the time.

We have often pondered over why it`s lasted so long. No-one seems to know for sure, and no-one probably will. It`s probably just one of those things- like life- which should just be marvelled at, and not endlessly discussed over why and how. Although we have and we do!

Burn on little bulb

Chris M---Part of the reason that the little bulb burns on an on is that it is never turned off. Turning a bulb on and off shocks the filament and bulb by going from room temp to white hot and back again. This thermal cycling makes the filament expand and contract and helps the filament to fail due to metal fatigue.---Marc

There is another issue with turning a bulb on: surge current.

The current through a filament is limited by its resistance, following Ohm's law (Current = Voltage/Resistance). However the resistance of the filament _changes_ with temperature. When the filament is at room temperature, its resistance is about 1/10 of its value at operating temperature. All other things being equal, when you turn on a tungsten filament lamp, about 10 times the normal current will flow for a brief time as the filament heats up, with the current dropping quickly to the steady state value.

During this surge, if there happen to be any thin spots in the filament, they will heat up faster than the rest of the filament. These thin spots can overheat and melt/break before the rest of the filament gets hot enough to limit the current.

-Jon

Yes, this is one of the main reasons for light bulbs to 'burn out' - I am sure that several people have walked in to a room, turned on the light switch and got a Bright flash of light and then nothing

I have experience with this, I used to work for a lighting company, and we made 12kw dimmers (100A); we had two test bays each with 48x1000w light bulbs

To limit the risetime on the dimmers to prevent or reduce EMI, we ran approx 40 turns of #6 around a 3.5 inch torroid

When the filaments were cold, and you turned up the dimmer - you could hear the inductor 'whine'

Another time, we needed to do a test on a 277v dimmer, we didn't have any 277v light bulbs, so we just used 2 x 110v light bulbs in series, as long as you ran the power up and down slowly, there was no problem

But, one day - a technician came in and turned on the light bay to 100% full power immed. on one bank of bulbs !

The 48 x 1000w light bulbs exploded, threw glass everywhere, and to top it off - the place where we kept our packing materials was right below the lamp bay - all the white-hot filaments fell into the box, and caught the paper on fire !

There are some companies out there that made a positive resistance device simular to a GeMov, it allows the light bulbs to slowly come up in power to prevent this inrush current

Mike
www.inretech.com

See Don's web site on www.misty.com for more detailed bulbous explainations!

Originally posted by Jonathan:
There is another issue with turning a bulb on: surge current....

Click to expand...

<font size="2" face="Verdana, Arial">Is there perhaps also the possibility that over those hundred years someone tiptoed in and changed the bulb?

Brightnorm

Thats why you have to be careful not to touch $13 Surefire LAs and, even more importantly, $30 stage bulbs! The oils from your fingers burn off and pop goes the lightbulb (hmmm...that sounds familiar for some reason)

The main reason for such color variation is the ammount of phosphor applied to the LED. I read somewhere on this board that somone has developed a whole new way of doing it--but right now the process is very unscientific. They just slop some on. This is a huge part of the angry dog urine green luxeons.

Also--over driven Nichias turn turquoise. That could be another suspect of the color variation here.

Yup. A given "white" led will show a different hue depending on how hard it is driven. The Opalec drives the LEDS just about at spec.

The reason that the oil from your fingerprints will cause this to happen, is that the expansion (heating) / contraction (cooling) of glass is all the same on all parts of the bulb

When oil gets on the bulb that area of the glass expands and contracts at a different rate than the other glass around it, and such - the glass breaks

That is why it is very important to install those very bright projection bulbs and other Halogen bulbs using a piece of cloth or tissue to prevent the slightest amount of oil from your fingers

I worked in the Theature Lighting field for 13yrs; did the hardware design/software for several high end lighting control consoles

Mike
www.inretech.com

The oil from your fingerprints can have a slightly different (but related) effect. Because of the UV and heat, it will oxidize to a dark spot, with will absorb light and cause a hot spot on the glass...which will of course expand differently (as Mike suggested) but could also heat that bit of glass up past the melting point.....