- Digital signage in retail is coming more and more. The problem: Content sometimes can’t be read or isn’t even recognized because the devices are too weak in brightness. But how much brightness is necessary? invidis took a look into the matter.
To rate a display by his brightness is a challenge. Tests often can’t be carried out in real surroundings because of the missing time and space. It is been relied on the given data and the first test which took place with another light ratio and not where the display is going to be installed.
Current displays have a large bandwidth of brightness levels. Starting at 450 Candela to 3.500 Candela or even more. This makes a big price difference.
Currently there are two opinions to work against the sunlight. First of them is to increase the brightness of the display dramatically (High Brightness). At ISE in Amsterdam the display manufacturer “Dynascan” had a 55” display with 7000 Nits (Nits = Candela).
The second option is to use the sunlight as an amplification for the backlight. This is possible with trans-reflective displays, which let the sunlight go through the LCD layer and reflect it again. The advantage: The backlight is designed for an average power of 750 Candela the rest is done by the sunlight. This thought is really good as the input is normal with the backlight compared to the high brightness displays where the input and operating costs increase enormous.
We tested 6 displays and compared them visually to each other: Samsung DM48D, Samsung LH46OMD, Samsung PE46C, Samsung OH46D, LG 47WX30MW und NEC X462HB.
The brightness starts at 450 cd. We choose a low brightness to do a comparison with TV-sets which are unfortunately still used in shop windows. Further devices for the comparison have 700cd, 1500cd, 2500cd and 3500cd. Also part of the test is a 700cd trans-reflective LG display and a high brightness NEC device which has a special coating to guarantee an optimal playback in a bright surrounding.
The test took place this year in May on a free area with southern exposure and thereby in a natural light. The light ratio changed during the recordings because of the clouds. The surrounding light was between 90.000 and 100.000 Lux.
All displays had the same resolution of 1920×1080 pixel. The distribution takes place through a professional HDMI-splitter with identical cable length.
Videos and pictures were recorded with a normal digital camera. This causes banding effects. The reason for that is the different refresh rate of the displays in ratio to the sampling of the camera sensor. It is not possible to get the different refresh rates with the sampling of a normal camera sensor. This effect has nothing to do with the quality of the displays.
If you want to be on the safe side you should choose a device with 2.500 Candela. Depending on the place of installation, trans-reflective displays can also be used after the real light ratio has been checked. When in doubt you should choose a trans-reflective Display with a brightness of 2000 Candela. Displays with brightness to 750 Candela are not suitable for shop windows.
Please watch the video of the High Brightness Shootout 2015: