Hey! Hi. This page is was duplicated at the Training Courses site, with new edits, at: Measuring Light
Please use this new site, since it will be the most up to date and it will come with new features. Thanks!
Imagine that you have joined a non-technical employee Quality Assurance Project. You might have many goals: I want to learn a bit more about the technology of movies, or, I want to be part of a well trained team that keeps customers happy… and you might have many different purposes for those goals: If I can help create happy customers, they come back more often…or, if I have good control of the basic skills, I can use them to get even more important skills, becoming more valueable to my team and company. To accomplish these goals and achieve these purposes, there are many things that need to be done.
Of course, your goals and purposes must align with the quality policies set by the CEO of the company (Cheif Executive Officer). The CEO might say that your small village theater can only get so much money for seat and carpet replacement and do the best with what we have, but we are not a premium movie palace. Or, the CEO might say, spare no expense, this is the Flagship Theater for the entire chain and it has to be the best. Or, something in between.
Usually there is a way to be true to your aspirations and stay within the boundries set by the boss. No matter what, the boss would never want us to compromise safety, or show a bad image on the screen, or let the sound get full of distortion. They probably want to make sure that each patron is satisfied with what the facility and what the staff have to offer, even if it can’t be the perfect place. So this includes wanting an educated staff that is able to communicate intelligently with patron and tech staff.
And that is what we are going to do, a little at a time – learn to communicate about the performance of the facility with the patrons, a little at a time. In this section we are going to learn about measuring light levels with simple equipment …your iPhone, right?
So, if at first you don’t have the organizational support to download DCPs onto a USB drive, then get the DCPs into the Media Player/Projector system right now – you can still download some audio and light measuring tools, and experiment with them until you can use them easily in a dark room.
The twin article to this, about sound, is at: 6) Measuring – Sound
Unlike the many free and not-always-easy-to-use audio tools for the iPhone, measuring light levels from the cinema screen doesn’t offer too many choices, and none are free. Don’t misunderstand, there are many that will measure light the way that a light meter does for a photographer, but we need one that measures the light bouncing from a screen.
Technically, measuring light from the light source…straight from the projector in this case…is measuring ‘illuminance’, while measuring the projector’s light that is reflected by screen is measuring ‘luminance’.
There is a screen company named Harkness which has developed a program for the iPhone named the Digital Screen Verifier. It costs $30. They write that the tool is made for cinema engineers. Hopefully that won’t scare you from using it. What they mean is that it is a professional tool. They don’t want people thinking that it is a toy. They can’t say it out loud, but they are rightfully impressed that they are able to get the iPhone to do so well and so consistently.
$30 is real money, and in addition to promising not to have math on any tests, we won’t chastise anyone who can’t allocate the funds from the food and shelter finances. We appreciate that spending money on tools that the company may not reimburse you for also might cut into your lifestyle funds. But we’d like to say:
“Just spend it. You are on the road to being a Pro, and a pro spends money on their tools. Professionals also practice and they also speak to other team mates using the proper language.”
Even though the Cinema Test Tools DCPs are made so you can compare blocks of white against black without a meter, the eyes have a hard time with absolutes. When there is no real white light on the screen, the eyes find the brightest area and the brain computes that as white. With a test tool reading, it is easier (and better) to say to the tech that “the luminance has slipped 6 candela”, rather than guess and say…”Gee, it seems darker I think, maybe.”
You may get some arguments about using this particular tool from your tech team. Not because they don’t want you involved, but because the Screen Verifier wants to send its data to the Harkness Screen Archiver. Many people have a problem with your data being shared with someone outside of your organization’s computers. We have all read about the security problems with big stores and large websites, and we should imagine that small stores and small web companies also have problems. If you buy this program, just make certain to turn off the data export feature, or get permission to send your data to the Harkness database. And send Harkness a note saying that you want a method to send the data to your own web server if your team won’t allow external storage. Maybe they are working on this already.
The other thing to know about this tool is that the measurement units are in an old format named foot-lamberts (abbreviated ftL or fL). The standard (worldwide) for measuring luminance is candela per square meter. It is best that you start your life as a professional with the proper words. You can even be more hip if you say ‘nits’, because that is what all the cinematographers use. A ‘nit’ is a candela per square meter.
There is another reason for using the Standard International Unit (SI Unit). If you say to a tech, “It looks like we are 2 foot-lamberts different than last week, it doesn’t sound like much. 2 of anything doesn’t sound like much, and can be easily written off as pilot error. Actually, since the standard brightness of an auditorium is supposed to be 14 fL, 2 fL is 1/7th or over 14% of the expected amount. Losing that much light on the screen is Not. A. Good. Trend.
On the other hand, since 1 foot lambert is about 3 and a half nits (actually 3.426), if the meter says 2 fL, that’s 7 nits (candela per square meter) – or more, out of the expected 48. That really feels more like a reportable problem, not so much a pilot error, and certainly a negative trend that needs to be handled.
Hopefully enough people will send messages to Harkness to explain why you want them to follow international standard…it isn’t like you don’t like Mr. and Mrs. Lambert’s famous son – he really was a fascinating person. Just explain that you only have so much time and learning the right way the first time is better for you. (Harkness email: [email protected])
All this well be discussed in more detail. But, get the Harkness tool, and learn how to follow its directions and get comfortable using it. Remember, you will be using it in a dark room, after you’ve used another tool to an measure audio level. You must be prepared for when that moment arrives to pick up your instrument like a musician grabbing a solo, right there at the end of the DCP, you can take a luminance reading.
Make sure to write and yell at us for using some maths. We won’t do it too often, and we just forgot this time. Sorry.