Advantages of LED technology
by Lukas Pescoller, 27.07.1999
FAG-VRG has started in 1995 to study the LEDs as a
possibility to improve conventional densitometers and spectrofotometers in terms of
stability, life time, robustness, measurement speed, industrial manifacturing etc. and has
presented on Imprinta in 1997 the first densitometers (FAG ScanPen, FAG Vipdens 444) based
on LED technology. Nowadays most of the measurement devices distributed by FAG are based
on this new, revolutionary LED technology.
1.1 industrial manifacturing becomes easier
The mechanics and electronics of an LED based optic is much more simple than
the mechanics of lamp based optics because of several reasons:
- LEDs have already a narrow light emitting
angle. Therefore there is no need to add special optical or mechanical components
like lenses, reflectors etc. to focus most of the emitted light to the measurement patch.
- the light of LEDs is 'monochromatic'.
These effects that the reflected light has not to be splitted for filtering purpose by
mirrors, or optical fiber or any other, costly optical or mechanical components
- the revers order of monochromaticity (monochromatic
light source, white receptor) results in one single electronic (fotodiode,
logarithmic unit etc.) which is common to all colour channels (Cyan, Magenta, Yellow,
etc.). Only one third (in case of 4 colour densitometer) of electronic components is
needed compared to the conventional, lamp based, technology, where there has to be a
seperate electronic (or at least part of it) for each channel.
1.2 quality of LED based units
Because of the simplier mechanics and electronics, errors in assembling can
be avoided. So the LED technology fits perfectly to the FAG logo: Simply
perfect, perfectly simple. Moreover there are some side effects that improve
the quality of the LED based units.
- an extreme long life time (about 200.000 hours)
combined with a high measurement speed results in a high stability in terms of emitted
light. Example: one LED is on for about 10ms per measurement. If we make about 500
measurements a day, 200 days a year, 10 years, then the LED is on for about 2:48
hours out of possible 200000 hours!
- LEDs have high intensity in terms of emitted light.
In adition the entire emitted light can be reflected and will be measured by one single
fotodiode (no optical splitting of light). With the conventional technology the reflected
light had to be tailored, a certain percentage for each colour channel. Therefore LED
technology results in more light, higher signals, higher resolution and more
stable measurement results.
- a short measurement time results in low load
to filters. Filters will be exposed to light for 2:48 hours only in 10 years!
- Low current consumption will make
the units smaller: two batteries will produce enough current for some hundred thousends of
- higher direction independence than
with lamps will make the units simplier (one LED instead of 2 lamps)
2.1 New products
With the LED technology there can be developed new products with new
specifications because of the simplicity of the optics, the low current consumption, the
direction independence, smaller apertures, low costs, extreme long life time
- scanning densitometers and spectrofotometers (FAG
Scan Pen and Speedy Eye) need extrem short measurement time, extreme long life time, and
extreme low current consumtion of LED technology because there will be made much more
measurements as with normal densitometers or spectrofotometers.
- low cost spectrofotometers and multiple colour
densitometers (FAG Vipdens 2000) with 'monochromatic' LEDs instead of expensive grids for
environments where robustness is verry important (press room, embedded units etc.)
Production of competitive units in terms of
- independency (battery driven)
- guarantee of 3 years