Is there (and should there be) a good standard way to measure a light's ouput?

[Tom Dowler]

The single most frustrating thing I find when new lighting products come on the market, is truly understanding what their output is.

In the "good old days" you could just compare wattage of tungsten units for a good, if slightly flawed comparison. But now with tungsten, HMI, LED, plasma, etc technologies, it can be really difficult to understand - without using it - whether a given fixture will really provide the horsepower you need for any given situation.

Obviously there are variables like flood/spot, but surely we should be able to establish a sensible scale that we can apply to all fixture types that allow us to understand what the output is.

Or am I misunderstanding something?

 

[David Mullen ASC]

Lux, lumens, and foot-candles are measures of light output. For movie lights, there is often photometric data provided by the manufacturer in foot-candles for spot and flood over distance.

 

[Stacey Spears]

You can measure with a light meter, but that gives you output, not color or spectrum. When you install a softbox, or grid, the light output and color changes.

One thing that is obvious is that lights don't match the reported color/tint setting on the light. e.g. I have an Arri L5-7, L7-C and S30-C. None of them match the setting on the dial nor do they match each other. I use a Sekonic C700 to get the color temp close to each other, which works pretty well. It is a pain in the rear, but worth the effort to match them.

 

[Michael Tiemann]

You can measure with a light meter, but that gives you output, not color or spectrum. When you install a softbox, or grid, the light output and color changes.

One thing that is obvious is that lights don't match the reported color/tint setting on the light. e.g. I have an Arri L5-7, L7-C and S30-C. None of them match the setting on the dial nor do they match each other. I use a Sekonic C700 to get the color temp close to each other, which works pretty well. It is a pint in the rear, but worth the effort to match them.

Yup. It's why I bought a c700.

 

[Tom Dowler]

Lux, lumens, and foot-candles are measures of light output. For movie lights, there is often photometric data provided by the manufacturer in foot-candles for spot and flood over distance.

Right, but the distances aren't necessarily the same in Arri's documentation compared to Kino's - so there's no standardization. Knowing that light A outputs 1000 footcandles at 9 feet, and light B outputs 850 fc at 11 feet means I can't do an easy apples-to-apples comparison, at least not in the same way I can do an apples-to-apples between a 650w tungsten fixture and a 2kW tungsten fixture.

What I'd love is a new unit - let's call it a Mullen - which is the max output, in footcandles, or lux or lumens or whatever, of a given fixture, at a set distance.

That way, no matter the type of fixture, if I'm researching what to rent or buy, I instantly know that, hey, light A will give me 10 Mullens, whereas light B will give me 20 Mullens.

 

[Tom Dowler]

it can be really difficult to understand - without using it - whether a given fixture will really provide the horsepower you need for any given situation.

You can measure with a light meter.

Right, but I'm talking about a universal shorthand for output so that I don't have to go around measuring every possible light to know which ones are most likely to be suitable for a given shoot.

 

[Aaron Lochert]

Something that is often overlooked is beam fall off.

A light might have one meter reading in the very center, but read darker toward the edges of the beam. So even when all things are equal such as beam angle, distance and intensity, one light will actually have a higher total output because it has less fall off than the other. On the flip side this also means that, if two lights have the same total output (lumens), one will have a brighter hot spot than the other, and thus have a higher perceived throw than the other. That means that both lights suit their own purpose: one for punch/throw, one for area coverage. A 'Mullen' isn't going to tell you this. You'll just see that one is more and therefore "better."

Any single unit of measure is not going to tell you the full story. It's like pixel resolution -- a useless number when it's by itself.

 

[Satsuki Murashige]

What I'd love is a new unit - let's call it a Mullen - which is the max output, in footcandles, or lux or lumens or whatever, of a given fixture, at a set distance.

That way, no matter the type of fixture, if I'm researching what to rent or buy, I instantly know that, hey, light A will give me 10 Mullens, whereas light B will give me 20 Mullens.

Wouldn't it be simpler to just have the manufacturers standardize the distances at which they specify their footcandle output? Anyway, due to the inverse square law, you can pretty much guess what the equivalent outputs would be even if the distances don't match exactly...

*Also, part of the reason for different target distance specs is due to European manufacturers like Dedo and Arri using meters instead of feet as a base unit. So maybe we should just keep it simple and keep everything in meters. Multiply by 3.3 for feet. Should be close enough to be useful.

 

[Mark K.]

Standardised distances, and standardised declarations of beam angle (including measurements for both spot and flood for focusable lights) is the key I think.

I keep seeing these ridiculous videos from trade show floors where a manufacturer will say simply "this light outputs this many LUX", and the interviewers will go 'Wow', as though that information means anything whatsoever. Without knowing the beam angle and distance at which a measurement is taken, the output figures mean absolutely NOTHING.

Same thing for saying things like "this light is equivalent to a 2k tungsten"... a 2k tungsten what? A fresnel at full flood? A frenel at full spot? An open-face light at full spot or flood? A scoop light? A soft light? A spot light? A space light? These vagaries in lighting manufacturers descriptions are infuriating, and make it very hard to come to purchasing decisions in such a heavily saturated market.

I'm hopeful though, that the smart ones will start to realise this and respond according in how they describe and inform people about their fixtures (the way the smart ones are already measuring and reporting their TLCI figures).

 

[Nick Gardner]

I think this is where experience comes in. You work on 100 jobs with a whole bunch of different lighting gear, and you pay attention. Also trust your gaffer.

Nick

 

[Mark K.]

I think this is where experience comes in. You work on 100 jobs with a whole bunch of different lighting gear, and you pay attention. Also trust your gaffer.

Nick

Experience is all well and good, but if manufacturers want us to try out their newfangled lights on productions, it needs to be clear what those lights are actually capable of doing. And standardisation in a few basic aspects of reporting photometrics, could go a long way towards helping that.

Without any clear idea, the only sensible thing to do is stick with the fixtures you know.