High Lumen Projection – the way to a brighter future
Thorsten Köhler, Managing Partner of luxury private cinema builder Die Zwei – Heimkino GmbH, elaborates on the special challenges of high brightness projection.
The brightness for projection in commercial cinemas has been set to 14ftL (48 nits) almost 20 years ago now. This has been documented in the DCI Digital Cinema Specification V1.0 (July 20th, 2005). Content that is produced for the consumer market is mastered towards a 100 nits target for Standard Dynamic Range (SDR). That means if you calibrate your projection to that ftL/nits-level, you´re on the safe side: respecting the creator´s intent, assuring the content is displayed as it should be. But even these days, even this brightness level is not easy to achieve with projection on larger screens, which leads to a lot of installations not even able to meet this long-lasting standard, leaving the client with a dark and dull image.
With the introduction of HDR (High Dynamic Range), these safe and standardized boundaries have been broken down. HDR content is mastered to a minimum of 1.000 nits – a brightness level, that even the brightest commercial projectors can hardly achieve on a reasonable sized screen. To mitigate this dilemma, the concept of tone mapping was introduced. This is a mechanism, that tries to adapt the high dynamic range to the capabilities of your projector/display device. This works reasonably well but cannot be as good as using a display device that achieves the desired brightness right from the start.
This is where high lumen/brightness projection comes into play. With higher end residential and/or professional projectors, with lumen ratings ranging from 10.000 to over 20.000 and even 30.000 lumen, you can easily achieve a brightness of several hundred nits measured on screen. This gives you a lot more headroom for HDR tone mapping. You can now dial-in the standard brightness level of the movie image to a reasonable value, but still having enough headroom to have highlights pop-out if required. The effect is achievable relatively easy in dark scenes with lights easily popping out of the dark background. But it gets more interesting when it comes to highlights in an already bright image. Imagine a well-lit laboratory, but the computer screens and LEDs flashing on all the devices and machines in the scene still pop out.
To be able to achieve this, you either must dial down the overall brightness of the image with a standard projector, or you go with high lumen projection.
Besides HDR content, another great advantage with high power projectors is, that it allows to experience 3D through 3D glasses in the same brightness as SDR content. If you are a 3D fan, it is a sight to behold to experience 3D content with SDR brightness on a large screen.
For high lumen projection, we at “Die Zwei - Heimkino GmbH” are aiming for a range of 250-300 nits peak white brightness measured off screen. This can only be achieved with high-end residential or professional projectors – we use a selection from Barco, Christie and Sony for this purpose.
This brightness comes with a list of challenges that need to be taken care of and differ significantly from standard brightness projection:
Contrast / Black Level
For a given projector´s contrast, raising the overall brightness inevitably raises the black floor as well. If the contrast of the projector is too low, this leads to grey instead of black in lower light scenes. A lot of the high lumen projectors do have contrast values of 4.000:1 and below which make them unusable for high brightness projection in a private cinema setting. The black level would just be too bad. In our projects, we aim for a contrast of at least 7.000:1.
Screen Material / Structure
Throwing 10.000+ lumen onto any surface will highlight every small irregularity. A screen material that appears to be totally even at 100 nits can become unwatchable at 200-300 nits. For woven fabrics, it is obvious that finer is better. But even PVC screens, that appear to be very flat and smooth at first sight, can become an issue as even very small bumps can be perceived as a structure, especially on bright moving objects like clouds on a blue sky.
In-room Light / Reflection
A dark room helps avoiding reflections back to the screen which can harm the images contrast and also increases the immersion as you are not reminded all the time that you are actually sitting in a room and are not being part of the movie.
Throwing 10.000+ lumen onto a large white surface screen turns it into a huge light fixture, illuminating the whole room. Using dark and non-reflective materials at least in the front part of the cinema room becomes even more important with high lumen projection.
Safety Measures
High lumen means high laser output which can become a safety issue, exposing the audience to high power, highly concentrated laser light. Most of the high lumen projectors out there in the market are rated as class 3, which require specific safety measures to be considered during installation and operation. Hazard zones are defined by the manufacturers to be respected for their products to avoid direct exposition of the eye to the laser beam – especially for children. Countermeasures to reduce the hazard level include careful selection of the mounting position, consideration of the actual laser level being used, and the selection of the lens throw ratio.
Noise Level
Last but not least, as a side-effect, high brightness means high power. High power means high heat dissipation. High heat dissipation requires a lot of fans to move the hot air out of the projector. Lots of fans lead to lots of noise. Hence our standard approach for high lumen projection is always to plan for a dedicated projection room. This makes ventilation easy and has a lot of other advantages as it does not interfere with the room design and allows an easy installation.
As a conclusion, there are a lot of specific aspects to consider that become relevant when moving from standard brightness to high brightness projection. A lot of details that are no issue at all or that can be easily mitigated with standard brightness, need special attention with high brightness. Experience tells, that every person reacts differently to a brighter image. In general, a bright image is perceived better as it appears to be more vibrant to the viewer with better, more saturated colors. However, brighter can easily become too bright, especially in a light-controlled, dark environment.
That is the reason why we at “Die Zwei" always recommend to our clients to visit us in our showroom to try it out before deciding which route to go. We have a fixed installation of a Christie Digital Systems M-4K25 RGB which allows us to demonstrate a wide range of different brightness levels ranging from the standard 100 nits (and even lower) up to 350nits on a 184” screen.
“Die Zwei” are pioneers and evangelists for high lumen projection. However, the constraints are shifting and as cinema (DCI) as well as the residential market moves to higher brightness images. Reflected in the upcoming CEDIA EMEA RP23 video recommended practices - where we are currently contributing to the working group – the expertise required to implement will become more common. If you are in need of such expertise, we can help you to come to a literally brighter future.
Contact: info@diezwei-heimkino.de