A few weeks ago, I wrote that one of the major changes that has taken place in the Tech Metals space was in the lighting market. Fluorescent lights work by having electrons strike the atoms of a rarified gas in a glass tube, stimulating those atoms which then emit ultraviolet photons. Those photons then strike Phosphor molecules that convert that high-energy ultraviolet light to the visible light that we read by. Oh, in case you didn’t know, if you are willing to sit under a bare fluorescent light, compact or otherwise, then you are highly trusting of the quality control of the manufacturer, because unless their phosphor coating is extremely uniform and complete, some nasty UV light is going to leak out, which is just the stuff to cause skin cancer. Keep those fluorescent lights behind plastic or glass, everyone, it’s safer.
That aside, a fluorescent light is made by taking a glass tube and using a liquid suspension of the Phosphor Particles to coat the inside of the tube. Once the liquid is evaporated, the glass tube is heated to the point that the glass softens and lets the phosphor particles adhere to the tube. The tube is then finished by filling with gas and sealing. The fluorescent particles then do the job of creating visible light from UV.
The best phosphors of today use technology metals, like yttrium and cerium as carriers, and terbium and europium as dopants and light emitters. Someone realized a long while back that while the phosphor particles are less than 10 μm across, it’s only the surface and just below it that interacts with the UV photons. So, when tech metals became a lot more expensive and a lot more difficult to obtain, several lighting companies decided to begin making phosphor particles by making a tech metals-free carrier particle, then just coating that carrier with phosphor material. The result in terms of lighting was the same, and the cost of the tube was the same or lower due to reduced usage of high-priced technology metals.
Now, the consensus belief is that we are in a transition from fluorescent lights to LEDs. The question asked by a reader centered on the possible effect on technology metals demand due to this change. Perhaps, while each LED contains less phosphor material, demand for tech metals might rise because a lot more LEDs are required.
I think this question of number used versus material needed per unit is easy to answer. A typical LED has a luminous efficiency of about 110 lm/W, and the devices are typically 1 W power, containing roughly a 1 mm2 gallium nitride chip with a phosphor coating of about 4 mg/mm2 (according to a patent issued to Nichia) The same specifications for a T8 fluorescent tube are that luminous efficiency is about 90 lm/W, but power consumption in a 900 mm tube is about 30 W with an internal area of 456 cm2 and (according to a GE patent) roughly 2.5 mg/cm2 phosphor coatings.
What the above tells us is that a single T8 tube of 900 mm length will make about 2,700 lumens of light, and contain about 1,140 mg of phosphor. To make the same 2,700 lumens of light, and perhaps of superior quality, we would need about 25 LEDs using a total of 100 mg of phosphor. Yes, it would seem that the triband phosphors utilized contain almost exactly the same amounts of technology metals, because the mechanisms for generating the visible light are basically the same for an LED and a fluorescent lamp. The amount of phosphor, and thus tech metals, required per generated amount of light is decidedly lower for LED than for fluorescent. Note that we didn’t discuss power consumption in lighting. Yes, the LED lights also use less power, but they need decidedly less tech metals to do this.