A few weeks ago, I was contacted by that person who pointed out that, among other things, that ‘Most display contrast ratio tests are performed in pitch black rooms…….if you measure displays in ambient light, rather than darkness, you get very different results’. Well, Duh! We’ve been banging on about that for years. He later claimed that ‘LCD innovation has been at a standstill for decades’, which is probably the silliest claim I have ever heard and on that basis, I suggested he should read Display Daily.
Anyway, he persisted and then I found out that Sharp was a client for the front-lighting technology from Azumo. So, I said, “If you can get Sharp to talk to me about why they chose the technology, I’d be interested”. He did, and so in the end I found myself on a Zoom call with execs from Sharp’s display business (Frank Schaffer and Mark Horner) in the USA and Mike Casper of Azumo that makes the reflective technology involved.
It was only later that I realised that Azumo is the new name for Flex Lighting. Ken reported on the company’s technology a couple of years ago so I won’t get into the weeds. For details of the technology, see Optimizing Frontlighting for Reflective LCDs.
It was interesting to hear the views of a customer as well as the views of Azumo.
Sharp is good at low power displays, based on its version of the ‘Memory in Pixel’ technology which maintains the pixel in a fixed state with very little power consumption when used in reflective mode. That technology can be combined with its skill at making IGZO backplanes that allow a better aperture ratio, which means lower power consumption, in transmissive modes and less light blocking in any mode.
The 5″ IGXO-R display uses less than 150mW at 60Hz refresh, but can be slowed right down for even lower consumption, down to 40mW. Even an 31.5″ UltraHD module uses less than 2W. (all values without the frontlighting)
Reflective displays are great when the sun is bright, but in the dark, they need illumination. If you illuminate from the back in a transmissive mode, you have to develop a transflective (transmissive and reflective) mode that tends to reduce the reflectivity in that mode and the transmissivity in the other one, so both are compromised. However, if you have an efficient front-light, you can optimise for the reflective mode and avoid the compromise. Sharp calls its technology IGZO-R.
IGZO-R + Azumo
Sharp is using the Azumo front light technology and combining it with its reflective LCDs. The lightguide technology has been in development for 16 years. The key benefit is that it is very thin, which means that the optical features in the film, used to direct the light that has been injected at the side of the film into the desired direction, are very small. Small features mean that even in very high resolution (Sharp can support 300ppi reflective IGZO colour displays), the lightguide, which is typically 30-50? thick is not visible from the front. As Ken explained, the accuracy in directing the light into the LCD is critical in achieving good performance. Despite the small features, Azumo claims that 99% of the light can be re-directed towards the LCD, so its features are small, but accurate.
The result is a display that has 15% reflectance and 30:1 contrast ratio. Although that’s low contrast compared to transmissive displays, it’s very good compared to print, and has the ability to display video with full colour, which print can’t do! It has long been a problem for reflective displays is that it has been very hard to achieve good colour, video performance and low power. Qualcomm invested a huge amount in trying to do this and companies such as Liquavista and others have tried. The most recent we have reported on is ClearInk (Clearink Driving on with Low Power Display, but try a search on the website for ClearInk and you’ll see a lot more articles).
Mainly for Mobile
At the moment, the Sharp displays with the frontlight technology are mobile devices although Azumo has new equipment that could support displays up to 21″. There’s no theoretical limit, that’s just the size of the production equipment it currently has.
Sharp has a 31.5″ IGZO panel that could use the film if the equipment was available. I think that could make a great display for outdoor applications, such as use in Drive-Thru restaurants, for example. E Ink has been improving its colour performance, but is still well away from good video. However, at the moment Sharp has just a 5.0″ display that uses the IGZO-R technology.
Sharp shared with us a video on Vimeo that shows how the display works in front-light mode (below). I’m nervous about videos when I haven’t seen the product ‘in real life’ and I haven’t seen the reflective displays since SID in 2019, since when they are said to have improved a lot. However, it has been my experience that under really strong light, simulating something close to daylight, reflective displays can look great, but often lose a lot in colour and contrast when front-lit. If the Vimeo videos are accurate, the front-lit performance is impressive.
The official statement from Sharp was
“In short, because we are the only ones that have a component that works on their reflective LCDs. The longer story also includes a history of Azumo servicing several of Sharp’s customers for a few years to prove we were dedicated to it, Sharp performing a full audit/assessment of our supply chain to verify our quality, Sharp honoring their warranty through the Azumo process, and Azumo signing up sales rep organizations which align with Sharp’s coverage.”
Thanks to Azumo, this article has been ‘liberated’ to be freely available and does not count towards the free article count!