Lighting 101: Key Lighting Terms You Need to Know

By Brooklyn Tong

August 3, 2021

What are Lumens?

When purchasing any type of luminaire, Lumen is a crucial lighting term to look for, as it helps the user to understand and choose the most suitable one. It measures the light output from a luminaire, with higher lumen translating to having a brighter fixture and lower lumen translating to a dimmer fixture.

You can determine a rough estimate on how much lumens you need through calculating the square footage of the area, then multiplying that number by a universal foot candles measurement for different common residential and commercial settings:

For example, if you have a 100 sq ft. bedroom then you would need 1000-2000 lumens (100 x 10, 100 x 20). 

A fun fact about lumen is that for every square meter on earth, the sun puts out 127, 000 lumens. A word of advice from RDA, do not look at the sun directly unless you have adequate eye protection. 

What Does Wattage Mean?

Wattage is another common lighting term that shows up in all luminaires. It is the amount of power required for the luminaire to produce the lumen output. The higher the wattage, the more light it produces, however, with a higher wattage the operating costs for your luminaire increases.  In most scenarios, you would want the wattage to be lower assuming your lumen requirement is satisfied. It is worth noting that Incandescent and fluorescent light sources would require more wattage to produce the same amount of lumens as an LED light source.

Lighting Efficacy

Light efficacy is a follow-up lighting term of wattage and lumens. It measures  how well the light source produces visible light and it is calculated by lumens per watt. Most products typically have this measurement provided due to the increasing importance of efficacy nowadays. Nonetheless, it is still very simple to figure out light efficacy of a given product based on other measurements. Simply divide the total lumens produced by the luminaire by the wattage required to power it. For example, RDA ORA4-LED80 produces 8827 lumens and has input wattage of 78. 8827 divided by 78 gives an efficacy of 113 lumens per watt consumed.

Lighting term-lighting efficacy chart based on different types of light

 The US Department of Energy believes that huge energy savings can be made by switching to LEDs, cutting business and homeowner electricity bills by $50 billion a year. With improved efficacy of lighting, the US is actually projected save 490 terawatt-hours of energy by 2035. This is nearly twice the amount of energy that the Energy Information Administration predicts will be produced by solar power in 2035.

 According to the U.S. Department of Energy, cool white LED lighting products can produce 60–92 lm/W, compared to 10–18 lm/W for incandescent bulbs and 35–60 lm/W for Compact Fluorescents (CFLs). However, low-quality LED lighting products that are not designed properly may be no more efficient than incandescent bulbs. 


The lighting term voltage represents the pressure from an electrical circuit’s power source that pushes current through a conducting loop enabling them to power devices. There are two types of voltages- Alternating Current (AC) or Direct Current (DC). Alternating Current alternates between positive or negative polarities hence the name, while Direct Current always has the same polarity, being either negative or positive. The most common Alternating Current voltages in regards to lighting are 120, 240, 277, 347 and 480. 120-277V and 480V are typically what RDA offers in most of our luminaires. An everyday example of DC voltage would be a battery and most often DC voltages in lighting are 12 and 24. 


Other common terminologies would be line voltage and low voltage. Line voltage is the amount of voltage which a power line delivers to its destination or the point at which it is being consumed and in lighting this would be regarded as AC voltage. In North America, 120V AC is what is most frequently used in residential applications, 277V is typically used in commercial applications and 347 or 480 would be applied in industrial applications. Lastly, low voltage is typically defined as 50V or less and in most lighting applications low voltage would be DC voltage. Examples of lighting applications for low voltage would include landscape lighting or under cabinet lighting. 


Color Rendering Index (CRI)

CRI is the measurement of the quality of how colors look under a light source, compared to how they would look under sunlight. The index ranges from 0-100, with 100 indicating that the colour would look the exact same under this light source as it would the sun – a perfect match to natural light. A general rule of thumb is that the higher the CRI rating is, the better the colours will look under a luminaire. This rating is important to consider when planning for retail or museum applications, when specific lighting that brings out the best of what it lights up is the key to success.

Lighting term color rendering index

Color Temperature

Color temperature describes a light’s appearance from a light source. This lighting term is very often referred to as Correlated Color Temperature (CCT). CCT is measured in degrees of Kelvin (K). For most lighting applications, it will range from 2700K to 6500K. The lower the CCT, the “warmer” or more yellow the appearance of the light source will be. On the other hand, the higher the CCT, the “cooler” or more bluish the appearance of the light source will be. For context, it is commonly accepted that 6500K is the best Kelvin temperature to match natural daylight.

It is very important to keep color temperature in mind when planning lighting for different applications. A warmer color temperature will create a more cozy, inviting space, while a cooler color temperature will feel brighter and more energizing. An office space, for example, is more likely to have cool, bright color temperatures, while an evening restaurant is more likely to have warmer, cozy color temperatures. Another example to consider is different kinds of shops. A jewelry store would ideally have very bright, cool temperatures to enhance the already-sparkling diamonds they sell. This could be around 5000K. On the other hand, a butcher shop would be more likely to have a warmer color temperature to bring out the freshness of the meat.

Lighting term color temperature scale


Light Distribution Types

Light Distribution is the projected pattern that a fixture will disperse onto a surface. There are two commonly recognized standards for light distribution types – NEMA Distribution and IESNA Distribution. Looking at NEMA Distribution, this defines a luminaire’s light distribution by its horizontal and vertical beam spread. These patterns are well-suited for defining flood and sport light applications. There are 7 NEMA beam types:

On the other hand, IESNA Distribution patterns define a luminaire’s light distribution more specifically by the shape of the area that is lit by the luminaire. These distribution patterns are typically used when designing with area or roadway lights. There are 5 IESNA beam types:

A special thank you to Ed Wynne of RDA Lighting for his expertise putting this blog together!