What is Design? Week 2: Determining Illuminance using Lumens and Lux


Cool White, Neutral White, and Warm White Noribachi CLUs

Last week, we dove straight into color temperature and how it works with different elements in the interiors we create like fabrics, skin tones, and ambient lighting. I hope you learned a little about using light in relation to how it affects us, like how warm white lighting creates a sense of coziness or how cool white lights help us focus on what we’re doing because of their perceived intense brightness.

This week, we’re going to take a closer look at the brightness of lights and how to use lumens, lux, foot-candles and efficacy to apply lights in given situations.

When referring to the brightness of a light, there are few terms you should be aware of when you go shopping, starting with the most important—Lumens (lm).

A Lumen is the metric unit derived from the amount of visible light emitted by a light source. The higher the lumen count, the more light that source produces.

Lux (lx) is the metric unit that measures the intensity of light, as perceived by the human eye, when it hits or passes through a surface. One lux is equivalent to one lumen per square meter.

A Foot-candle is the non-SI unit that measures the intensity of light cast upon a surface widely used in the American lighting industry to calculate the adequate levels of light in one square foot. One foot-candle is equal to 1 lumen per square foot or about 10 lux.

Indoor Foot-candle & Lux Recommendations*

Type of Space



Public spaces with dark surroundings (Corridors, Nightlight, Radiology room)



Simple orientation for short temporary visits (Dining rooms, auditoriums)



Working/living spaces where visual tasks are occasionally performed (Sitting rooms, Office lounge, Locker room)



Performance of visual tasks of high contrast or large size (Copy room, Cashier stands, Supply room)



Performance of visual tasks of medium contrast of small size (Laboratories, Teller station, Kitchen)



Performance of visual tasks of low contrast or very small size (Demonstration hall, Emergency outpatient room, Operating room)



Performance of visual tasks of low contrast or very small size over prolonged period of time (Jewelry and watch manufacturing)



Performance of very prolong and exacting visual tasks (Precision Arc Welding)



*Source: Oregon State University

So let’s break it down. Take my my living room for example, which measures 15′ x 18′. It has two windows on one wall and a closet along the opposite wall.

The number of lumens needed in a room depends both size and type of the room. Looking at the chart above, it fits in the third type of space–waiting and sitting area. A living room is used for sitting, reading, watching TV, and social interaction.


Basically, it doesn’t need to be super bright to be an effective space, but it you should be able to see clearly.

Warning. This involves simple math! But don’t be alarmed, there are no formulas to remeber from algebra. : )

Step 1: Gather the measurements of your room in feet

  • Length x Width = 15′ x 18′


Step 2: Multiply the room dimensions together to find the number of square footage of the room.

  • 15 x 18 = 270 SQ FT


Step 3: Referring to the chart above, a sitting or living room requires between 10 and 20 foot-candles. We’ll make it 15 foot-candles to keep it simple.

Since 1 foot-candle is roughly equivalent to 1 lumen per square foot, we must multiply the required foot-candle measurement by the square footage of the room to get the number of lumens in a light we need

  • 15 (lm sq ft) x 270 (sq ft) = 4,050lm


Step 4: Using the amount of lumens we need, 4,050lm, we can now go shopping for the luminaire that will produce this much light.

Yay! I love shopping. The great thing is that it’s even easier to find and purchase the right amount of bulbs since many manufacturers now include the lumen count right on the packaging.

LED Lighting Facts Label

Select LED manufacturers, like Noribachi, have partnered with the Department of Energy’s LED Lighting Facts program. This means that we can display the LED Lighting Facts logos and labels that contain important lighting information such as the Lumen output, the wattage of the light, the efficacy (Lumens per Watt), the CRI, and the color temperature of the bulb.

Since there are not many bulbs on the consumer market that produce 4,000lm right off the bat, we will be needing a number of bulbs to help us achieve the adequate amount of light we need. One of the legacy bulbs we sell that are A25 100W replacements (pictured above) that use only an amazing 13W. The warm white version of this bulb produces 1,150lm.

So to be safe, we will get four of these bulbs since the fixture we have installed also has four mounts. That amounts to 4,600lm from a single luminaire.

But what if your room isn’t wired for pendant lighting? That’s okay! In fact, that’s even better!

The great thing about lighting is that it’s flexible. You can have multiple lights of varying intensities so that you can control the amount of light in the room for different situations. Have lights pointing up, down, against the wall, covered or uncovered.

Honestly, this is where your personal taste and design comes into play, because you can choose to have pendant lighting, down lighting, lamps, bounced lighting, etc. The options are endless–as long as you have a rough idea of the amount of light you need, have fun playing around with different lights until it works for you and looks great!


SoreAs an interior designer, I love lamps. I love that you place them in different parts of the room–on the floor in a corner or on a side table next to the couch– you can mix and match them to create a space that is uniquely yours, while also being completely functional!


If you wanted to light larger areas like an outdoor sports field or a warehouse, specific requirements will be a little more difficult to pinpoint. Lighting contractors or some manufacturers (like us!) will complete simulations for an added fee so that the right amount of light and the placement of select lights is maximized in the space given.


This designer used two types of lighting as well as making use of ambient lighting, the first is obvious and the second, not so much. The pendant lanterns are a cool spherical element in an otherwise angular room. The second type of lighting, if you look closely is recessed into the ceiling. The number of the them, suggests that individually, they are not bright, but when lit together create a nice ambiance in the room, accented by the lantern luminaires.

can2 Can

Our single 021.HEX LED engines produce an amazing 3,315lm with just 23 input watts. These make the perfect can/downlights for a wide range of domestic applications including entry way and corridor lighting.

They can be dimmed and are available in all color temperatures, custom built to your specifications.


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