This prototype shows the use of liquid cooling for the phosphors in a laser/phosphor projector. Currently, the mainstream way to maintain the required temperature for the phosphors in a hybrid system is to put the phosphors on a rotating wheel and spin the wheel at high speed. This approach has two problems. The first is obvious, you have a rotating wheel in the system, much like a color filter wheel in a lamp-based single panel projector. Elimination of this moving part would be a desirable change in hybrid projectors. The second is less obvious: rotating the wheel can only reduce the problem, not eliminate it. This phosphor loading issue when phosphor wheels are used is one of the reasons why hybrid projectors are currently only available up to about 4000 lumens. One important issue in liquid cooled phosphor systems is to allow for expansion of the liquid without distorting or even destroying the liquid container. Li discussed several approaches to this problem that would apply to either passive systems with natural convection or active systems with a pump to circulate the liquid. Perhaps one of the most interesting approaches Dr. Li discussed was the use of phosphors in suspension in the liquid and the use of a pump, as shown in the figure. He suggests that if phosphor aging is an issue in very high output projectors, the projector could be designed so the closed phosphor system could be replace as a cartridge, much like an ink-jet cartridge is replaced now.