The latest (1999) TALGO-hauling diesel locomotive, recently
developed in Germany and Spain, uses LED-based head and rear
lights. The headlights are actually a multi-LED display yielding
white light; the rear lights are ordinary high-power red lights.
Efficient blue LEDs -and lasers- have been available only recently, using
Gallium Nitride as base material. The key point is that blue is necessary
to get white light from LEDs -by mixing red, green and blue LED-emmited
beams (as in TV). We lacked the blue ones until recently.
Instead of using these multiLED structures, another way of getting white
light is employing ONLY a blue LED which in turn emits its light onto a kind of
phosphorescent layer. The latter becomes excited and happens to emit
white light. I think most of the the "white LED" devices they are already
selling use this technique, but I've heard the light is actually slightly
bluish...
The white LEDs of the TALGO loco seem to be true white multiLED.
Javier Fraile
The following was submitted (8-2000) by:
Javier Fraile
Talgo's white LED lights are just clearance lights
("position lights," as we would say [a/k/a "marker lights"]); the main headlight
is an ordinary dual halogen lightset above the front
window. It is not quite visible in some photos. The LED headlights
are just "parking lights." I am attaching a pic where the main headlight can be
appreciated perhaps a little better (shown below). Incidentally, the new
ADTranz/Talgo electric locomotive for 350 Km/h also has the
same kind of White/Red LED arrays for head/tail lights.
Indeed, white LEDs are not yet powerful enough,
even if arrayed, to replace conventional illumination
involving high luminance (but they are fine for
MODEL trains !)
