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TVs Reaching Maximum Comfortable Luminance
TVs are cranking out 300 -1000 cd/m² APL and with a maximum for HDR at 2,000 cd/m² and projectors up to 50K lumens, while small pitch LEDs can put out 3,000 cd/m². The HPA (Hollywood Professionals' Association) Tech Retreat and Pete Putman responded with the question, "Can a Display Be Too Bright?" Then he asked, "Should we be focusing on screen contrast, instead?". He highlighted that, in the past, CRTs were just around 100 cd/m² and cinema screens struggled to hit the SMPTE recommendation of 16 ft-L (55 cd/m²). Pete Putman provided a number of AV industry "rules of thumb" for CR:
Figure 1: TV in Fully Lit Room
TVs are cranking out 300 -1000 cd/m² APL and with a maximum for HDR at 2,000 cd/m² and projectors up to 50K lumens, while small pitch LEDs can put out 3,000 cd/m². The HPA (Hollywood Professionals' Association) Tech Retreat and Pete Putman responded with the question, "Can a Display Be Too Bright?" Then he asked, "Should we be focusing on screen contrast, instead?". He highlighted that, in the past, CRTs were just around 100 cd/m² and cinema screens struggled to hit the SMPTE recommendation of 16 ft-L (55 cd/m²). Pete Putman provided a number of AV industry "rules of thumb" for CR:
- For passive viewing (reading a book/magazine): 7:1 minimum
- For classroom / meeting room presentations: 15:1 minimum
- For analytical decision making: 50:1 minimum
- For immersive viewing (movies, VR, etc): 80:1 minimum
- Ambient light in a classroom measures 100 lux
- 16:10 screen measures 120 inches diagonally (4.175 m² area)
- 100 lux (x) 4.175 = 417.5 lumens (this is the effective ambient ‘black’ level)
- Recommended contrast ratio for classrooms = 15:1
- 417.5 (x) 15 = 6262.5 lumens
- Using a 6000-lumens projector with a matte (1.0) screen
- That's a pretty clear calculation for a projection system.
- For a direct view display (e.g., LCD or OLED or LED), at the same size (120" is too large):
- 4.175 m2 = 45 ft² screen area
- A 120-inch LCD, OLED, or ILED display
- 6000 lumens / 45 ft² screen = 133 ft-L
- 133 ft-L = 455 cd/m², which is a very bright display
- Limiting contrast ratio is only 15:1– with no eye strain for comfortable viewing
- In a dark room, visual fatigue is created after sustained viewing
- If the room is darker, an older projector, rated at 1,000 lumens provides 300 lumens after calibration. There is lots of ambient light and also reflections when the lights are on, even though the walls were painted grey.
Figure 1: TV in Fully Lit Room
The measurements of the black level and the brightness of objects varied a lot between the three lighting situations. The first column shows measurements with all the lighting on, the second with the front lights off and the right with all off.
Table 1: Impact of Exterior Lighting on Black Levels
Table 1: Impact of Exterior Lighting on Black Levels
Putman then went through the calculations to show that what he measured matched what he would expect from the projector but couldn't quantify the limiting contrast ratio as the meter he was using could not measure the darkest regions. However, in the darkest setting, the image was good enough for viewing. Switching to a newer brighter projector (from BenQ) was a lot brighter when the lights were on but didn't improve the lights were off as there was a lot of reflection from the room.
Table 2: Projector Luminance (cd/m2) Under Varying Light Conditions
Table 2: Projector Luminance (cd/m2) Under Varying Light Conditions
The results show the BenQ W1500 projector is a lot brighter at 1300 lumens and the full white has much more luminance. However, the limiting contrast is 51:1 because of the reflections, which is good but not great. A darker room is needed with viewers with darker clothes.
Figure 2: Contrast Pattern
Figure 2: Contrast Pattern
The BenQ projector may be brighter than the old one, but the light from the screen cause the room surfaces to be more obvious. Milliken said that 50 ft-L (171 cd/m²) is a practical upper limit for displays in a darkened room, but Putman thinks this may be too bright. He attended a test of a 3.3mm pitch LED wall in a large theatre that had 200 cd/m² (58 ft-L) full white, but some viewers, well away from the screen, thought it was too bright for comfort.
Putman’s LG OLED is around 130 cd/m² (38 ft-L) when ISF calibrated, and in daytime provides 2:1 to 10:1 contrast which is comfortable. However, at night, it lights up the whole room but at about 65:1 limiting contrast ratio - good but not perfect for immersive viewing.
Samsung's 144" (12'/366cm diagonal) MicroLED Wall TV can provide 1,600 cd/m² (468 ft-L) at full white which, with a typical (APL meaning on-screen images of 100-300 cd/m² (29-88 ft--L). Some viewers find the image too bright for long term viewing. The high brightness means that the room is lit up well enough to write notes and watch one HDR clip.
LEDs are already moving into cinemas. However, even 'throttled' back, with HDR content, on-screen brightness was up to 200 cd/m² and the whole cinema was 'lit up'. It did make it easy for staff to deliver food and drink, but the trainers on one viewer (shown in the image below) measured 10 ft-L!
The fundamental conclusion from this effort was that displays are bright enough now and gong to >1000cd/m2can be too bright for comfort
Source: This material was excerpted from an article in Display Daily.
Putman’s LG OLED is around 130 cd/m² (38 ft-L) when ISF calibrated, and in daytime provides 2:1 to 10:1 contrast which is comfortable. However, at night, it lights up the whole room but at about 65:1 limiting contrast ratio - good but not perfect for immersive viewing.
Samsung's 144" (12'/366cm diagonal) MicroLED Wall TV can provide 1,600 cd/m² (468 ft-L) at full white which, with a typical (APL meaning on-screen images of 100-300 cd/m² (29-88 ft--L). Some viewers find the image too bright for long term viewing. The high brightness means that the room is lit up well enough to write notes and watch one HDR clip.
LEDs are already moving into cinemas. However, even 'throttled' back, with HDR content, on-screen brightness was up to 200 cd/m² and the whole cinema was 'lit up'. It did make it easy for staff to deliver food and drink, but the trainers on one viewer (shown in the image below) measured 10 ft-L!
The fundamental conclusion from this effort was that displays are bright enough now and gong to >1000cd/m2can be too bright for comfort
- Milliken's recommendation of 1998 that 50 ft-L/188 cd/m² is enough is still valid
- The best way to get good value is to work back from the target contrast ratio
- The best way to get good results is from changes to the viewing space, not by simply cranking up the display luminance.
- There is still a challenge to get to 80:1 CR in most environments.
Source: This material was excerpted from an article in Display Daily.