While the entertainment world was busy romancing the new generation of LED sources, physicists and electronic techs were busy marrying two technologies that would soon yield another lamp source to rival LEDs in efficiency and surpass them in other areas. The new LiFi solid-state plasma lamp is a tiny bulb, radio-frequency power supply, and electronic circuit that puts out a tremendous amount of light in a very efficient manner.
Just how tiny is the bulb? They’re so small that you could probably fit about 36 of them in a Tic Tac box, which is the number of Tic Tacs that normally come in that box. That’s because they are roughly the same size as a Tic Tac. But the power supply is slightly bigger, coming in at about 4-inches by 4-inches by 2 and 5/8 inches, so the entire package with the bulb, power supply, and circuitry is still very compact.
The bulb has no filament or electrodes. Instead, it is filled with gas and metal halides. The power supply creates an electric field at a very high frequency in the radio band. The electric field transfers energy to the gas and ionizes it, creating a ball of plasma gas. The heat produced by the plasma evaporates the metal halides and then they combine with the gas and give off light — a bunch of it.
There are two models of the LiFi lamp at the moment that the manufacturer, Luxim, is pushing in the entertainment industry; the LiFi-ENT-30-01 and the LiFi-ENT-30-02. (To see the spectral power distribution curve for each, see the chart below.)
According to the manufacturer, the ’01 gives off 11,000 lumens with 230 watts input and the ’02 gives off 17,000 lumens with 280 watts input. Do the math and you’ll see that they range from 47.8 lumens per watt to 60.7 lumens per watt. Compare that to an incandescent lamp at about 17 lumens per watt or to an MSR 700 short arc or MSR 2000 short arc with an electronic ballast at 80 lumens per watt or 86 lumens per watt, respectively, and we see that it compares favorably but it doesn’t have the highest luminous efficacy. So what’s the big deal?
The big deal is that the plasma source is so small that it is easier to gather and use the light it produces than the light produced by a short or medium arc lamp. Therefore, the light emitted can be more useful and the fixture efficiency can be higher.
{mosimage}Besides being an efficient package, the light produced by the LiFi also has a color rendering index (CRI) of 91 for the 01 and 94 for the 02. That means that it renders colors very well, especially compared to an MSR, which has a CRI of about 80. The reason for the higher CRI is more easily understood when you look at the spectral power distribution curve of the LiFi, or how the light is distributed through the color spectrum. It’s a much more continuous spectrum than a typical discharge lamp and it is fairly well balanced between the red and blue ends of the spectrum.
The balance between the red and blue ends of the spectrum, of course, is also an indication of the color temperature, or in the case of a discontinuous source, the correlated color temperature (the equivalent color temperature of a lamp with a continuous spectrum).
And because it has no filament or electrodes, it has a relatively long life of about 20,000 hours for the 01 and 10,000 hours for the 02. One of the downsides is that, at the end of the rated life, the output is expected to be about half. That’s not a fabulous maintenance of lumens.
But the upside definitely outweighs the downside, and it won’t be long before you’ll start seeing these lamps in the field.
Already, at least two entertainment lighting manufacturers have jumped on the LiFi bandwagon; Robe and Ocean Optics. Robe has a prototype fixture using the lamp in a moving yoke assembly that looks to the naked eye to be comparable to a typical 575-watt fixture. It has a beautifully uniform field because the arc doesn’t wander between the electrodes and the optics don’t image the electrodes, since there are none. It is expected to hit the market some time in 2009.
Ocean Optics is already shipping a fixture with the LiFi lamp source — the Nemo. The color-changing ellipsoidal reflector spotlight uses an ETC Source Four front end, the SeaChanger dichroic color mixing engine, and the LiFi lamp in a custom-built back end. The fixture specs claim an output of 15,000 lumens withw only 180 watts of input power and 15,000 hours rated lamp life. The source is another version of the LiFi called the ENT-30-OL.
It’s unlikely that the LiFi will overtake LEDs or even come close to gaining as much market penetration in the near future. But it’s also likely that more and more entertainment lighting and video manufacturers will build luminaires around this unique lamp source. Tic Tac anyone?
