My Samsung LCD TV broke down after 3.5 years of service. After failure analysis, it appears that the LCD panel is dead. You would expect it but the price to repair it exceeds the price of a new TV …

Then what to do with this TV? LCD TV is electronic boards and an LCD panel in front of a backlight. The backlight is still working as well as electronics. Why not use it as a light source ? It is still difficult to find a device that can generate an almost constant brightness over an area of ​​about 0.5 m². This could be used as a light table, a diffuse light source for photography or macro photography. In my side I think rather to use it as a source of extra lighting in trompe l’oeil, a a fake window.

Let’s see how to transform an LCD TV Samsung LE40B620 which is 101cm diagonal to a lighting source.

Unmounting the TV

	The stand of the TV have been removed beforehand. The opening of the unit is done by removing all 15 screw present on rear of the TV. The screws are located on the periphery of the housing (red dots on the picture). The plastic part can be easily removed after full unscrewing.
	We discover at the back of the TV the three main boards present in most LCD TV: the POWER board, which in this case includes also the inverter parts that are generating the high voltage (> 3000V) used for fluorescent tubes The MAIN board integrating connectivity and the main chips that are managing the device. It is connected to the TCON board by an LVDS cable. The TCON board is receiving images through the LVDS interface and is generating signals and timing required for LCD panel
	Après avoir déconnecté les haut-parleurs ( en bas à gauche et droite) ainsi que la carte de réception infrarouge ( en bas à gauche ), le chassis acier se désolidarise facilement de la face avant du téléviseur (pas de vis). En débranchant les câbles, en particulier le câble noir d’alimentation, on peut voir à travers les fentes du chassis que le rétroéclairage s’allume immédiatement . L’écran reste quand à lui noir car la dalle LCD reste opaque. Une résistance de Pull-down doit être présente sur le carte Main, l’absence de connexion entraîne l’allumage du rétroéclairage. Il n’y a donc pas de modification de l’électronique à prévoir pour forcer l’allumage de l’éclairage, il suffit de déconnecter les câbles !
	After disconnection of speakers (bottom left and right) and infrared receiver board (bottom left), the steel frame can be easily disengaged from the front of the TV (no screws). When disconnecting the cables, especially the black power cable, you can see through the slots of the chassis that the backlight turns on immediately. The screen remains black however because of the LCD panel that remains opaque. A pull-down resistor must be present on the MAIN board, no connection causes the ignition of the backlight. There are therefore no modification of the electronic expected to activate backlight, simply disconnect the cables !
	When removed diffuser filter, you can see 3 superimposed polarizing filters performing a first level of light scattering. CCFL tubes appears also through the filters.
	All filters being removed (3 polarizing filters, one filter diffuser), and you have direct view onto the CCFL tubes. Be careful not to bend the frame, it isn’t very rigid. An important twist might break the tubes.

Mounting light source

	Warning: the device have been replugged before putting back protections. This is very dangerous ! Some conductive parts on circuit boards are connected tomains (230V ~), but also other high voltage generated for CCFL tubes (> 3000V). Let’s have a look to the effects of the different filters on the light scattering. First on the photo at the letf is the light coming directly from CCFL tubes without the presence of any filter.
	After establishment of the three polarizing filters, a first level of diffusion is achieved.
	The last diffuser filter shows an almost constant brightness over the entire surface. It remains slightly possible to distinguish the alignment of the tubes.
	Reassembly is done in reverse order, possibly omitting some parts that are not useful for you : putting back the front steel frame front and screwing it. The thickness of the missing panel is easily caught by the flexibility of the framewor. the front frame is no more interesting for me, it takes space and is useless fixing the steel frame in the bottom plastic shell using screws + nuts fixing steel stiffener for the footage of the TV foot attachment About electronic boards, I myself have kept only the Power boards, other boards are useless.
	Final result : a TV format with a white front panel
	This light source is distributed on a surface of 0.44 m2. The brightness is surprisingly strong (see comparison below) due to the suppression of the LCD panel. The light temperature is quite cold.

Results

I tried to compare the results between this new light source and commercial bulbs. The photos were taken with the same sensitivity settings, aperture and speed. The color temperature was set on the camera for a fluorescent type. The photos have not been modified, so they can be used to compare the results under the same test conditions.

Overview	One detail	Lighting type
		Compact fluorescent bulb Power = 13W Color temperature = 2700K ( chaud )
		Compact fluorescent bulb Power = 18W
		Halogen bulb Power = 105 W
		TV panel lighting Power = No measurement

I don’t have unfortunately any bulb at home that rivals to light generated by this new light source. It probably equals to a compact fluorescent bulb of about 25-30W .

The color temperature is much cooler than bulbs. This is really visible in the photos above, but it is not a problem for photographic use if you take care is to enable the automatic adjustment of color temperature.

The spectral range obtained with our panel TV should be also better than average bulbs. Chromaticity is an aspect that is standardized for TV broadcasting , which is not the case for the general public lighting. TV manufacturers must ensure that the spectral content of the images is large enough to get closer to this standard. This is only possible with a backlight source of good quality, the LCD panel itself is only filtering this light flux coming out of the screen.

We can also see on those pictures the interest of having a diffuse light over a large area . Let’s compare the following two photo extracts :

Bulb lighting

Diffuse lighting

The shadow casted by the teapot on the left to the one on the right is much less pronounced, or non-existent, on the photo with diffuse lighting. Furthermore, the reflection of the light source on the object is not limited to a single point but to a larger area that is closer to a light source like a window.