[elhigh]

"Remote phosphor" speaks to the design of the bulb. Fluorescent tubes also use a remote phosphor design. An arc is struck and maintained down the length of the fluorescent tube, but it gives off almost exclusively UV light - not helpful. But the UV light excites the phosphor coating on the inside of the tube, which glows brightly in turn in the visible spectrum. Careful tweaking of the phosphor recipe allows the manufacturer to produce colors that are redder or bluer than true white.

Remember the funny-looking Philips LEDs with the orange tops that are nonetheless generate white light? Same deal.

It's worth remembering that phosphor bulbs do not generate pure white light, a blend of the entire spectrum. There are significant gaps in the spectrum that are nonetheless missed by the eye as complementary colors on either side of the gaps still blend to produce what is perceived as white light. But, in the example of a "cool white" fluorescent lamp, the red end of the spectrum isn't well populated, and flesh tones and food that rely on red for true rendition come out looking gray and washed out. This is why many food service establishments, regardless of the obvious cost savings to be had, do not employ that many fluorescent lamps where the food will be seen by the diners. "Warm white" fluorescent lamps help bring the red tones back, but then greens and blues are underrepresented and everything has a ruddy or orange cast. The solution is a mix of cool and warm lamps in the same fixture and indeed you will sometimes see that - looking directly at the fixture you can clearly see that there are two distinct colors of tube up there.

These remote phosphor LEDs work in a similar fashion. The LED generates a wavelength of light that isn't especially useful directly, but it excites a mix of phosphors that, in turn, generate visible light. I'm not terribly familiar with them but I suspect that, like fluorescents, there are gaps in the radiated spectrum.

That said, for use in cars what you want isn't an entire spectrum unless you're talking about fog lamps, license plate lamps, reverse lamps or headlamps. For turn and brake signals a highly specific output wavelength is acceptable, and even preferable over an entire spectrum.

For brake lamps, you want red. 650-700nm or thereabouts, the same color as a laser pointer. LEDs that generate specific colors are far more efficient per delivered lumen (for this purpose) than a white lamp. When the light passes through the brake light lens, everything but the red light will be filtered out, wasted. If all you're generating is red light, then NONE of your energy investment is wasted. Doing that you may be able to install a lower-wattage LED that is less likely to overheat in lengthy use, thus ensuring that it will last even longer and deliver even more bang for your buck.

Same goes for orange for your turn signals. Right around 600nm. No point generating light that you won't actually be using. Choose specific color LEDs instead, and save the remote phosphor white LEDs for places where a fuller spectrum is required.

Sorry for the lengthy response. I'm a bit of an amateur lighting nerd, it's one of my passions. As passions go it's a bit dry, but few things have ever captured my imagination as much as artificial lighting.