### Author Topic: Backlight brightness with TFT displays (5" and 7")  (Read 2931 times)

#### dshero

• Newbie
• Posts: 2
• Karma: 0
##### Backlight brightness with TFT displays (5" and 7")
« on: July 17, 2015, 10:31:52 AM »
I plan to design in a TFT display of yours into equipment that our company manufactures. I am looking at the following possible displays:
NHD-5.0-800480TF-ATXL#-T
NHD-7.0-800480EF-ATXL#-T
NHD-7.0-800480EF-ATXV#-T
According to the backlight specs, the 5.0 needs 60 ma@19.2V yielding 400 cd/m^2 luminosity. The 7.0(L) needs 60 ma@16V yielding 160 cd/m^2, and the 7.0(V) needs 60 ma@16V yielding 220 cd/m^2. I have the following questions:
1) Why does the 5" display need more backlight power than the 7" displays?
2) The higher backlight power appears to produce about twice the brightness on the 5" than what is produced on the 7" displays. Does this mean the 5" is going to appear overly bright or the 7" displays dim?
3) I am a little concerned with power consumption, so am wondering if I go with the 5" display, can I reduce the backlight current and still get good results?
4) Our equipment (runs 24/7) has a life > 10 years. Since the backlight has a decent, but shorter life of maybe around 20,000+ hrs, we will need to increase the backlight life. We plan to do this by reducing the backlight power when the display is not being looked at (most of the time). We would like to reduce the backlight current to maybe 10% instead of turning it all of the way off so that the display is still partially viewable instead of totally off. I assume that this should greatly increase the life of the backlight, is this a correct assumption, or will we need to totally turn off the current to the backlight to increase its life?

#### Saurabh_B

• Hero Member
• Posts: 355
• Karma: 10
##### Re: Backlight brightness with TFT displays (5" and 7")
« Reply #1 on: July 17, 2015, 11:08:05 AM »
Hi,

The rating for the backlight is 50k Hours, until it reaches half brightness.

You can also bring down the current supplied to the backlight to increase its life.

The led's for the 5" display do draw more current than the ones for the 7".

#### dshero

• Newbie
• Posts: 2
• Karma: 0
##### Re: Backlight brightness with TFT displays (5" and 7")
« Reply #2 on: July 20, 2015, 10:48:39 AM »
Thanks for answering my 4th question. Can you please address the first 3 questions I had? Namely, why does the 5" backlight need more power than the 7" display backlight, which results in twice the brightness for the 5" display? And why does the 5" display need twice the brightness? If I go with the 5" display, can I reduce the current to the backlight and still get good results, or if I go with the 7" display, will it be bright enough with the specified backlight current?

#### Michael_L

• Hero Member
• Posts: 356
• Karma: 33
##### Re: Backlight brightness with TFT displays (5" and 7")
« Reply #3 on: July 21, 2015, 07:19:42 AM »
The LEDs on the 5" display draw more current and are brighter, and therefore need more power.
The display doesn't "need" twice the brightness, that is just its typical brightness rating.  As Saurabh stated, you may reduce the backlight current, thus reducing power and effectively reducing the brightness.  Yes, the display will still look good, just not as bright.  Of course this is highly dependent on your application.  If you are using the display indoors, there should be no issues, however if trying to use the display outdoors in sunlight, you would not want to reduce the brightness.
Yes, the 7" display will be bright enough with the specified power ratings, we wouldn't sell it if it wasn't

If you would like to evaluate these displays, we offer whole kits to allow for quick and easy evaluation of our products.  If you are interested in this, please email nhtech@newhavendisplay.com with your inquiry, and we can help get you a list of parts you would need for the kit.
« Last Edit: July 21, 2015, 08:08:21 AM by Michael_L »

 NHD-7.0-800480EF-20 Controller Board and the backlight on a 800x480 LCD Display Started by dfanslerBoard TFTs Replies: 1Views: 2437 July 27, 2015, 10:08:23 AM by Saurabh_B MOVED: NHD-24064WG-AYYH-V Backlight current Started by Saurabh_BBoard Character LCDs Replies: 0Views: 1868 May 18, 2016, 08:00:24 AM by Saurabh_B NHD-7.0-800480EF-ASXN#-CTP: Nominal Backlight Current Started by emilzachariaBoard TFTs Replies: 1Views: 714 February 20, 2017, 08:25:44 AM by Saurabh_B Driving backlight for NHD-C0220BiZ-FSRGB-FBW-3VM Started by mhBoard Character LCDs Replies: 5Views: 3986 April 30, 2014, 04:15:00 PM by mh Backlight current limiting resistor Started by andresmdnBoard Graphic LCDs Replies: 6Views: 4470 April 28, 2015, 03:54:13 PM by JB