Watts, Lumens, and Lux. What do they all mean?

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In a nutshell, watts measure power, i.e., how powerful a video light is. Lumens are a measurement of light intensity. Lux is the light distribution over distance, meaning it’s an illumination measurement.

Lighting is essential to film and video production, so you must familiarize yourself with the terms watts, lumens, and lux.

Whether you’re shopping for your first affordable lighting kit or setting up lighting for a video interview, you will come across these terms, and you need to know what to look for and what to use.

In this article, I’ll do my best to break it down for you.

Watts

All lights, from the household bulb to the most robust industrial power light, are measured and labeled with watts.

As mentioned above, a watt is a measurement of power, measuring the rate at which the light consumes electricity.

60-watt bulbs consume electricity at a rate of 60 watts, 120-watt bulbs at a rate of 120 watts, etc.

Higher caliber lights will (obviously) necessitate more wattage to keep up their output.

Sixty watts is a standard for tungsten lights in homes or offices, whereas anything from 500+ watts is used for film and video production, with the most common being 500-2000-watt tungsten lights.

With LED lights, the wattage (and heat) produced from lights have been brought down significantly, but many still think about the wattage used by traditional tungsten lights when they need to figure out how powerful a light needs to be to a scene.

You might also like this article on what color temperature to use for video lighting.

Kilowatt-Hours

While not a term used for film or filmmaking, its relationship to watts makes it essential to understand. Where watts measure power, kilowatt-hours measure energy.

Energy is the capacity to do work, in this case, creating light.

Let’s go back to our example of the 60-watt light bulb consuming electricity at a rate of 60 watts.

Introducing time into the equation gives us the measurement of energy consumed.

For example, 60 watts over an hour gives you 0.06 kilowatt-hours used. Similarly, 120 watts over an hour would be 0.12 kilowatt-hours.

This usage increases significantly with strong tungsten lights, so those big film lights with 2000-watt Fresnels will consume much energy.

Kilowatt-hours are also how the power company keeps track of your electricity consumption.

While not commonly tracked in filmmaking, it can help determine how much you might owe if the space you’re renting for your location requires you to cover the power costs of your lights.

A professional LED lighting kit is the way to go if you’re worried about wattage overload and don’t want to shell out an insane amount of cash each month to pay the electrical bill.

Lumens

Arri fresnels outside

Lumens are a measurement of visible light and are commonly used to compare tungsten to LED lights.

Since LEDs are so much more efficient in their wattage consumption to light output, simply using watts to measure both tungsten and LED became inconsistent and complex.

A 1K tungsten’s brightness will not be the same as a 1K LED’s.

For this reason, measuring the actual light output, or lumens a light gives off, has become standard when working with mixed assortments of lights.

I mentioned in my article how many watts are needed for video production lighting, but here’s a quick reminder:

Tungsten lights generally achieve 12-18 lumens per watt consumed, whereas LEDs vastly outdo that with 30-90 lumens per watt.

Below is a table comparing lumens per watt for tungsten and LED lights.

Lumens per watt is a measure of the efficiency of a light source, indicating how much light is produced for each watt of electrical power consumed.

The values given are typical and can vary depending on the specific model and manufacturer.

Lumens per Watt Comparison Table

Lumens per Watt Comparison: Tungsten vs. LED

Light Source Lumens per Watt (lm/W)
Tungsten Lights ~12-17 lm/W
LED Lights ~80-100 lm/W

This table is quite basic and is intended to be a starting point.

So, back to our 1K tungsten vs 1K LED example, the 1K LED would be much brighter despite consuming the same wattage.

Remembering those numbers or checking your lights for a lumens rating can help you run some quick calculations to know how much light output you’re putting out between all your lights.

Lux (Luminous Flux per Unit Area)

This one might be tricky to wrap your head around. Unlike lumens, which are a measure of the light itself, lux are units of illumination.

More technically, one lux is one lumen of light evenly distributed over one square meter of space.

Put another way: lux measures light over a specific area.

Lux depends on distance since light spreads wider the further it travels, corresponding to a falloff in intensity the further from the source it moves.

The more surface area a light covers, the more dispersed it is, the less intense the light, and the number of lux goes down.

Lux is most commonly used in conjunction with lumens, and having a good light meter can help determine the best ratio to properly expose your scene in-camera.

How to decide what Lux to use

Keep in mind that distance is critical here. Just looking up online how many lumens equal how many lux will not necessarily reproduce accurately on your set.

A subject standing 10 feet away from a light producing 50 lumens will not be lit as brightly as a subject standing only five feet away.

The more distance the light is given to disperse over a wider area, the less reflective illuminance (in lux) you will have.

This also relates to watts since you may need to exchange your lights for something more powerful if the distance between your subject and the light cannot change.

Here are some guidelines you can use to decide what lux level you need for a scene:

Determine the Camera Settings:

  • ISO: A higher ISO increases the camera’s sensitivity to light but can introduce noise into the image.
  • Aperture (f-stop): A wider aperture (lower f-stop number) allows more light to hit the sensor, affecting the depth of field.
  • Shutter Speed: This should typically be set to double the frame rate for a natural look (e.g., 1/50th of a second for a 24fps video).

Understand the Inverse Square Law:

  • Light intensity falls off with the square of the distance from the source. If you double the distance, you get a quarter of the illumination on the subject.

Use a Light Meter:

  • A light meter can measure the lux level at the subject’s position. Adjust the distance and intensity of the light until you achieve the desired lux level per your camera settings and aesthetic preferences.

Consider the Subject and Environment:

  • Standard three-point lighting (key, fill, and backlight) starts at around 500 lux if you’re lighting a person.
  • For an interview or a portrait, you might want a softer light, so you could use a diffuser and reduce the intensity.
  • For a dramatic effect, like low-key lighting, you might want high-contrast lighting with higher lux levels on one side of the subject’s face and lower on the other.

Trial and Error:

  • Often, setting up lighting involves some trial and error. Adjust the lights and take test shots until you achieve the desired look.

Use Lighting Ratios:

  • A standard lighting ratio for video is 2:1, where the key light is twice as bright as the fill light.
  • You could use a higher ratio, like 4:1 or more, for more dramatic lighting.

Adjust for Motion:

  • If the subject is moving, or if you are planning to vary the distance from the subject during the shot, you may need to set up your lighting to accommodate the change in distance and maintain consistent illumination.

Post-Production:

  • Remember that you can make some adjustments in post-production, but it’s best to get the lighting as close to your desired outcome during the shoot to maintain image quality.

Note that these are starting points, and the specific lux levels will vary greatly depending on your needs and shooting environment.

For professional shoots, it’s advisable to do a location scout and test shots before the shoot day to ensure your lighting setup will provide the necessary illumination for your subject.

Conclusion

Like cousins, watts, lumens, and lux are related in the filmmaking sphere, as each one is connected indirectly to the other.

Knowing what each means and their relationship to each other can help you (or your DP) take total command of the lighting of your set and bend that light to your camera’s will.

Remember, a good light meter will go a long way in avoiding the headache of manually measuring these units.

Do you have any other thoughts or comments on watts, lumens, and lux to add?

Drop a line in the comments below.


Author

  • Nikola Stojković

    Nikola Stojković is a writer and filmmaker based out of Chicago. His short films have screened at festivals across the USA. When not shooting, he enjoys writing film reviews and playing his accordion, Fortunata.

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