PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 84 NR 8/2008 105

Maciej ZAJKOWSKI, Tomasz STALBOWSKI

Bialystok Technical University

LCD, DLP planar lighting fitting

Abstract. The LCD displays emit the luminous flux similar to lambertian emission and additionally allow to control the spectral distribution.
Conception of lighting fitting enabling the control of emitted luminous flux quantity and change of colorimetric parameters was presented.

Streszczenie. Wyświetlacze LCD emitują strumień świetlny w sposób zbliżony do lambertowskiego i dodatkowo pozwalają na sterowanie rozkładem
widmowym emitowanego promieniowania. Zaprezentowano koncepcję oprawy oświetleniowej umożliwiającej sterowanie ilością emitowanego
strumienia świetlnego oraz zmianę parametrów kolorymetrycznych. (Planarna oprawa oświetleniowa typu LCD, DLP).

Keywords: planar lighting fitting, LCD, DLP, display.
Słowa kluczowe: planarna oprawa oświetleniowa, LCD, DLP, wyświetlacz.

Introduction
Basic task of the lighting fitting is to make suitable
illuminance or luminance distribution on the working
surface. This task is dissolved through elaboration of light-
optical system, using the light source and elements forming
the light distribution e.g.: reflector, lampshade, lens. The
possibility of any decorating with mouldings the light bundle
through suitable reflector form or parameters selection of
lens or lampshade is the unquestionable advantage of the
typical constructions of lighting equipment. The problem
exists because of fitting geometry (mainly its depth) and the
possibility of controlling colorimetric parameters. The depth
of the lighting fitting causes that fitting must be built in
hanging ceilings or utilization of recess in ceilings or walls.
The control of colorimetric parameters is also inconvenient.
To obtain the colourful lighting with dynamic exposition, it is
necessary to bind in fitting several light sources with control
of spectral distribution. The RGB LED diodes are such
elements that can fulfil this task at present.

Conception of planar lighting fitting, leaning about liquid

crystals cells or arrangements micro-mirrors (figure 1),
gives control possibilities of both the spectral and luminous
flux distributions, through applying the planar optical
structures.

+10

~70

a) b) c) d)

Fig. 1. The conception of planar lighting fitting: a) module LCD with
side illumination, b) module LCD with back illumination, c) LCD
module with the lamp forming luminous intensity curve, d) DLP
module with the matrix of light sources.

Planar LCD fitting

Liquid crystals displays are built from basic elements:

- the liquid crystal cells,
- the electrodes,
- two thin foils of which one functions as the ploughland of
polarizer and second as the analyser,
- the light source (backlight) [1].

To form light bundle one uses backlight systems. There

is a little information about photometric propriety of

arrangements backlight in the literature. In our own studies
we mark LCD’s, because of luminous flux and luminance

distribution (figure 2). Analysing the distribution of the
luminous flux one affirms the considerable rotatory
symmetry of the light distribution, whose shape depends on
quality and the technology of the realization of LCD display.

Fig. 2. Building LCD display cell.

The light source are linear fluorescent lamps. The

fluorescent lamp with the cold cathode (Cold Cathode
Fluorescent Lamps CCFL) assures low waste of energy and
relatively large value of the luminous flux. Two technologies
are applied: the back and side illumination (backlight).

This kind of illumination allows to the cheap production

of monitors, but the serious technological limitation makes
up simultaneously. The CCFL backlight does not allow to
get the wide spectrum of colours, approximate or larger
than in standard kinescope monitors. The agreement is
standard in the case of monitors made in this technology
with the sRGB space of colours. Additional problem is to
create the monitor which has smooth illumination surface of
screen. The merit of "fluorescent lamps" is small quantity of
warmth, so the chassis of monitor can be comparatively
small in relation to the surface of screen and cooled passive
[2].

To the screen illuminations instead of fluorescent lamps

are also used the matrices of LED diodes (one module
consists diodes in the red, green and blue colour), which
they even step out in number a few hundred. In the result,
the surface of the screen is illuminated very evenly. The
user can correct the value of luminous flux of every diode.
The LED backlight is introduced in figure 6.

106

PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 84 NR 8/2008

Fig. 3. The example of luminous intensity and distribution of
luminance in equal lighting conditions, two various LCD displays: a)
HP, b) NEC.










Fig. 4. Type of back illumination

. Fig. 5. Type of side illumination.

Fig. 6. The LED backlight.

LED diode allows to get the considerably wider

spectrum (figure 7) of colours than standard LCD monitors.
The covered space of colours is AdobeRGB the most often,
however in the standard LCD it is sRGB or NTSCRGB. The
fault of such displays is high cost of applying this
technology and large quantities of warmth emitted through
diodes, which could deform planar plate of backlight, so it is
necessary to use active cooling chassis of display.

Fig. 7. Spectral distribution of LED and CCFL backlights.

The conception of fitting using micro-mirrors

Since several years light-optical devices using DLP

modules have been built. This are matrices of micro-mirrors
(figure 8), which are able to modulate luminous flux through
its reflection from mirror surfaces. Elements reflecting in
DLP modules lean out in the range ± 10 ° from the axis of
the DLP matrix.

Through arrangement of light sources in space (e.g. the

LED diodes), one can get the obtusity of the light bundle not
larger than 70 °. The colourful parameters of such light-
optical arrangement are the result of utilization of RGB LED
diodes.

PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 84 NR 8/2008 107

Fig. 8. The single micro-mirror in DLP matrix .

The laser is the modern source of the light. The

coherent radiation is its basic feature, and also
miniaturization [4]. Laser modules RGB (figure 9b) are used
in presentation and lighting systems, because of elimination
of expensive and inconvenient in exploitation light sources
like discharge lamps or high energy LED diodes. The
waste of energy in comparison with classic solutions got
lower about approx. 50%, causes enlargement of the range
of colours (figure 9a) to the level approx. simultaneously
95% range of colours perceived by the man. The light is
additionally polarized, and laser module is characterized by
high efficiency and lifetime about 55 000 hours.

Conclusions

Conception of planar lighting fitting leaning on the LCD

or DLP technology lets achieve and obtain the new guilds of
luminaire. Except of forming light distribution (dynamic with
utilization of the matrix micromirrors in the DLP technology),
such fittings let control in the dynamic way, and control of
colorimetric parameters like colour temperature or colour of
the light. Light, emitted from planar fitting, shows high
degree of polarization because of applying polarizing filters
in its construction. The construction of low-luminance
fittings is inconvenient in classic formulation, however it lets
utilization of planar structures (planar optical fibres) and
LCD or DLP technology, on projects and production of such
light-optical devices. The additional feature of devices
emitting the luminous flux through liquid crystals structures

or micro-mirrors arrangements is the possibility of image
presentation or production of dynamic light scenes, through
single optical construction, what has not been possible until
now, in the case of the classic constructions of lighting
fittings [3].

a)

b)

Fig. 9. The laser RGB module: a) CIE1931 space of colours, b)
building of laser module.

Financed by Ministry of Science and Higher Education –
No. W/WE/4/08.

REFERENCES

[1]

http://www.pcworld.pl

[2] de Gennes P.G,. Prost J: The Physics of Liquid Crystals,

Claredon Press 1993

[3] Dybczyński W.: Miernictwo promieniowania Optycznego, WPB,

Białystok 1996

[4] http://www.novalux.com/display/

Authors:

dr inż. Maciej Zajkowski, Politechnika Białostocka
Wydział Elektryczny, Katedra Promieniowania Optycznego,
ul. Wiejska 45D/218, 15-351 Bialystok,
e-mail:

[e-mail]

mgr inż. Tomasz Stalbowski, Politechnika Białostocka
Wydział Elektryczny, Katedra Promieniowania Optycznego,
ul. Wiejska 45D/218, 15-351 Bialystok