Innovation Special Planetariums 9 - Carl Zeiss Planetariums

Stars of the Latest Generation
Thomas Dannberg
Product development,
Carl Zeiss, Planetarium Division
Since the launch of our SKYMASTER
ZKP 4 Planetarium, the projection of
the starry sky onto small to medium
sized domes has gained enormously in
brilliance and realism. This is due to the
adoption of glass fiber projection principle
pioneered in our UNIVERSARIUM
and STARMASTER starballs. As a result,
the brightness of the stars was stepped
up by a factor of ten, while lamp power
was reduced to 50 %. Part of the light
gain is used to enhance the realistic
impression of the stars by making them
smaller.
Yet more brightness and brilliance
White-light LEDs (light-emitting diodes)
have been on the market for a number
of years, but it was long before they
advanced in performance to a level
efficient enough for star projection.
Meanwhile, high-output LEDs are available
and give good service in the latest
generation of our SKYMASTER ZKP 4,
adding another marked improvement to
star and planet projection. The optical
properties of high-output LEDs used
instead of halogen bulbs pay off several
times over.
14 Innovation Special Planetariums 9, 2012
Relative Spectral Power Distribution
1.2
1
0.8
0.6
0.4
0.2
0
400 450 500 550
Wavelength (nm)
600 450 700
Spectral distribution of the LED compared to the halogen bulb (manufacturer's data).
Favorable light spectrum
Given the nearly continuous spectrum
of the halogen bulb, the lens had to be
corrected for the entire visible range.
The LED, by contrast, requires a partial
spectral range only, which allows
the imaging quality to be enhanced
con siderably. Furthermore, the color
temperature of the LED used is 6,500 K,
which is substantially closer to the stars’
natural whiteness than the reddish halogen
light.
Higher luminance
The entire light of the LED (approx.
2000 lm) is delivered by an area of
3 x 3 mm² only. The resulting enormous
luminance and a newly designed
aspheric condenser system permit us
to increase star brightness three times
compared to the halogen bulb.
LED Halogen lamp
Better light distribution
The mechanical structure of the halogen
bulb with parabolic reflector causes
annular zones differing in illumination
and changing with the lamp life. The
LED emits its light extremely uniformly
over the chip area, which makes for
substantially greater efficiency in light
utilization.
Light distribution of the LED (left) compared to the
halogen bulb (right).