How to Estimate Lumens for Your Space

In order to provide adequate lighting coverage in a room, you'll need to figure out certain measurements. But you must first understand some lighting terms.

• Lumen – Also referred to as “brightness” or “light output,” a lumen is the measurement of a unit of visible light emitted by a source. When it comes to lumens lighting, this applies to multiple sources, including fluorescent, halogen, incandescent and LED. A standard 100-watt incandescent light bulb produces about 1,500–1,700 lumens.
• Lux - A metric term, this is one lumen spread over a square meter. While they measure the same amount of light, lux is the amount of light projected onto a surface.
• Foot candle – A light’s level of brightness one foot away from its source. Foot-candle measurements vary depending on the room type, due to the tasks performed within. Examples include garages, which usually need 80-100 foot candles, or 60-80 for home offices.
• Wattage – The level of electricity (or energy) a bulb consumes to reach its claimed brightness. Wattage is the measurement of electrical power. Different light sources, like fluorescent or LED, have their own lumen-per-watt ratios. For example, microwave ovens typically use 750–1100 watts, while dryers use between 1,800 and 5,000 watts.

Large spaces need more lighting than small rooms. For lumens' lighting capabilities, to find out how many you’ll need in a given area, you can start by measuring the room. Here’s how to quickly calculate square footage:

• Measure the length of the room.
• Measure the width of the room.
• Multiply the length of the room times the width of the room. This is your square footage.

For example, a room that measures 10 feet long x 8 feet wide has an overall size of 80 square feet.

To determine how much light a room needs, you must figure out the foot candles required. Among lighting professionals, it's the most common measurement unit used to calculate light levels in businesses and outdoor spaces. The Occupational Safety and Health Administration (OSHA) has workplace lighting standards to protect workers. OSHA requires a minimum of 30 foot-candles of light on work surfaces.

A foot candle is equivalent to one lumen per square foot. Making this foot candle-to-lumen conversion is helpful when calculating your lighting needs. You should account for the following factors:

• Room size: A room's size directly affects the number of lumens lighting needs. Larger rooms generally require more lumens to provide adequate lighting.
• Room functionality: Lumen amounts are heavily dependent on a room’s purpose. Task-oriented areas usually require brighter lighting to allow for more detailed, careful tasks, as with kitchen lighting. Meanwhile, dimmer, less severe lighting works well when ambient lighting is called for, like with bedroom lighting.
• Color and décor: Color(s), whether for the walls or ceiling, and specific furnishings can reflect and absorb light in a room. Lighter-colored object or glass, like mirrors, can refract light, bending and changing light rays' path. But darker-colored objects, like curtains, can absorb light, making rooms dimmer.
• Age and vision: With aging, your eyes may require additional light to maintain the same level of visibility. Therefore, consider your household’s ages and visual acuity (sharpness) when planning for lighting coverage requirements.

You can estimate the total lumens lighting needs for your room. Just multiply the room's square footage by the lumens per square foot (as previously determined). This gives you the total lumen count required for optimal lighting.

Here are examples of lumens per square feet (or foot candles) typically needed for different rooms:

• Living room (100 square feet) - 1,000-2,000 lumens
• Kitchen (stove) - 7,000-8,000 lumens
• Dining room - 3,000-4,000 lumens
• Bathroom - 7,000-8,000 lumens
• Bedroom -1,000-2,000 lumens
• Porch - 800-1,000 lumens

You can also determine lumens needed per square foot by calculating foot candles. Just multiply the room square footage by its foot candle requirement. For instance, a typical, 100-square foot living room needs 10-20 foot candles. If multiplied by 10 foot candles, the room would require 1,000 lumens.

Once you've calculated a room's measurements for lighting, you can ensure that you have the proper fixtures to promote better visibility. When purchasing lighting, designers and architects (and the product packaging) generally consider two principles of light.

• The qualitative aspect - Also called the aesthetic aspect, this focuses on lighting creating a cozy and pleasant atmosphere. With this aspect, interior beauty is enhanced, while decorative elements are spotlighted.
• The quantitative aspect - Also called the engineering aspect, it precisely calculates the amount of light required to ensure adequate brightness for daily activities. Known as luminous efficacy, it's a key indicator of lighting technology performance. It enables the comparison of different light sources' energy efficiency.

Lumens vs. wattage - It's crucial to understand the differences between lumens and watts.

• Lumens measure the brightness or light output of a lamp or lighting fixture, not the energy consumed.
• Watts measure the amount of electrical power a light source or fixture consumes. They indicate energy use, not light output.
• Mistakenly, people often believe that higher wattage equals brighter light. With technology advancements, lights with lower wattage, like LEDs, can produce the same or even greater light. Using lumens, rather than wattage, to determine lighting needs is more accurate and relevant.

LED lighting - Both a 60-watt incandescent lamp and a 10-watt LED light produce about 800 lumens. However, the LED light uses much less energy. Modern LED technologies can achieve 70-110 lumens lighting per watt. This is a higher luminous efficacy than legacy incandescent bulbs, which achieve about 14 lumens per watt.

Dimmers - You may prefer to install dimmers when planning for lighting needs. Dimmable lighting can dramatically benefit both energy and cost savings.

• Decreasing brightness can reduce your electricity consumption and prolong the life of your light bulbs.
• Dimmers provide more control over your lighting settings.
• A darker environment can promote a more comfortable environment, such as for early mornings or light-sensitive conditions, like migraines.

Color - You can use color temperature to determine lighting needs. Measured in Kelvin (K) degrees, this scale won't change a room's ambient temperature. Instead, it refers to the idea that some colors remind people of warmth, while others remind us of coolness. A higher K number indicates cooler light (like with blue), while a lower number indicates warmth (like with red).

You may also plan your lighting based on the color rendering index (CRI). It's designed to show a more realistic depiction of an object's true color. CRI measures how natural colors compare with sunlight under an artificial white light source. Many bulbs, including LEDs, incandescent and halogen light sources, have a CRI of 100, a perfect score. But fixtures scoring 80 or 90 will also provide effective lighting.

When it comes to lumens lighting requirements, these are only general guidelines. While they'll work in most spaces, they may not be applicable in every scenario.

• For a desired effect, rooms with dark walls and especially high ceilings may need additional lumens.
• Industrial spaces often require more lumens per square foot. This is due to the complicated, potentially dangerous nature of work being performed. For these locations, you can install specific light types, such as shop, wraparound or accent lighting. You may also want lighting with higher outputs, like LEDs.
• Commercial spaces, like retail stores, can utilize many of the same light types. But as they could have high ceilings and large spaces, lumen needs may have to be calculated on an individual basis.
• For both industrial and commercial facilities, you should check local regulations. You can then more accurately determine lumens per square foot requirements and recommendations.