How Much Light Do I Have? Footcandles, Lumens and Lux Explained!

lighting basics Aug 03, 2022

If you’ve ever sat down to attempt the purchase of new lights, one of the first questions you have is “how bright are these things?” and “are they bright enough for my lighting rig?”

While demo rooms and online videos can give you a rough estimate, neither is accurate enough to show you how the light will look in your space with your other lights.

So how in the world do we compare different lights, and how can we know if it’s going to be bright enough?

While I'd like to say it's an exact science, it simply isn't!  Comparing the brightness of 2 lights can be done with simple brightness readings, and that can give you a general idea of how the light will look, but it's not the complete story.  However, let's start at the basics, and then get more nuanced as we dive deeper!

How Bright is “X” New Light Anyways?

When we’re looking at product spec sheets, there are 2 different types of brightness measurement that we can take into account to compare a new light to what we currently have, or 2 compare 2 lights that we are considering.

The first measurement is lumens or the total amount of light output by the source.  This is a measurement of all the light put out across the whole beam of the light, and is useful when comparing the overall brightness of a fixture, but not all that useful for knowing if your stage is going to be bright enough.  

Lumens are a very rough measure - not that they're inaccurate, but they only tell you about 1 attribute of the light, and it's just not a complete picture.  Yes, it is the "raw" output from the light, but some of the things it fails to consider include beam and field angle, color temperature, color quality and your distance from the light.

To add to that mess, some manufacturers will also list "source lumens", which is the amount of light coming from the LED or lamp inside of the fixture.  This measurement is pretty much useless, as it doesn't factor in how much light is actually coming OUT of the fixture!

Another "bad lumen measurement" is when the measurement is taken with an integrating sphere - these devices measure 100% of the light coming out of the fixture - which while technically accurate, it's not all that helpful in the real world!

The 2nd type of measurement is foot-candles or lux, which measure how bright the light is at a certain point in space.  This is the measurement you need when you are figuring out how bright your stage needs to be, and this is what you measure with a handheld light meter.  This is far more useful to us in stage lighting because it allows us to see how bright the light will be at the point where it hits a person on stage - and when we combine that with the beam and field angle to find the size of the "circle of light" on stage, we can now calculate how many lights we need and how bright it will be.

Foot-candles and lux actually measure the same exact thing – lux is the international standard while foot candles are the English standard measurement, like meters vs. feet.  

1 Foot Candle = 10.76 lux

How Much Light Do I Need?

How much light you need on your stage is actually a really subjective thing to determine.  When I first began in lighting, I was taught that 80 fc was a great benchmark to hit for camera lighting, but honestly, in today's world, there are a number of factors that determine how bright your light needs to be, including:

  • Both the human eye and camera's distance from the stage: the farther people or camera's are from the stage, the brighter you'll need the light to be in order to look appropriate.
  • Natural and ambient light: stage brightness generally needs to be brighter than both natural light (from windows, doors leading to lobbies, etc), and ambient lighting from houselights in the space.
  • Color temperature: this one is a bit odd, but higher color temperature lighting tends to be perceived as brighter than lower (warmer) color temperature lighting.

One of the best ways to find the footcandle level that you are striving for is to look at your current lighting if you already have stage lighting in the space.  Does it meet the brightness you desire for the space?  Is it too bright, and you always dim it down?  

Compare that brightness level with new lights for a better idea of how the possible models of light will compare to what you already have.  If your lighting is relatively new, you may be able to pull spec sheets and find the brightness level at your throw distance. 

If your fixtures are older than 5 years, I would take anything you find on a spec sheet with a grain of salt - your older lights probably aren't outputting as much brightness as they did when they were new. A inexpensive light meter (affiliate link) can tell you how bright it actually is on stage!

What Else Matters?

When you’re looking at possible lights to purchase, you need to first decide what features are important to you, and then compare similar lights that are on the market.

Does having zoom matter to you?  What color temperature do you need?  How much power do you have available for this new light?  If LED, how many different colored LED’s do you desire?  RGB, RGBW, RGBA or more?

While brightness can be compared across different types of LED units, it’s not going to be accurate to compare different types of LED lights on the same scale.

Use the questions above to evaluate what you want to purchase and take the time to do a thorough comparison before you buy!


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