When it comes to the appearance of color, you cannot underestimate the importance of lighting. Yet, lighting can be confusing, as much of the terminology sounds similar but has vastly different meanings. For example, two of the most widely used terms — luminance and illuminance — can be easily misunderstood and mixed up. Since lighting is an essential component of color, we’ll discuss luminance vs. illuminance below.

What Is Luminance?

The definition of luminance is the amount of light emitted, passing through, or reflected from a surface. Think of a lamp shining in a dark room — luminance would describe the amount of light passing through the lightbulb.

The meaning of luminance is often used interchangeably with the term brightness. However, when it comes to luminance vs. brightness, these descriptions are not interchangeable. Luminance is a quantifiable, measurable characteristic. Meanwhile, brightness cannot be objectively measured — it can only be perceived. We recognize that a light source is bright or dim, making brightness the visual sensation by which we become aware of differences in luminance.

We measure the luminance to account for the human eye's sensitivity to different wavelengths of light. We can then provide a measurement that correlates with human perception of brightness.

When it comes to color decisions for your business, luminance can also describe a certain color’s perceived brightness. Fields that often use luminance measurements include electronics sectors responsible for designing display technology such as screens and digital signage. The automotive industry also uses it for lighting and road safety purposes. Generally, products that need to be created for the comfort and safety of human vision will ensure luminance measurements are within the necessary guideline parameters.

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How to Measure Luminance

Luminance is measured in luminance intensity, which measures how bright a beam of light is in a particular direction. There are a variety of units used to express luminance. The International System of Units (SI) uses candela per meter square (cd/m2), while in the U.S., the most common luminance unit of measurement is the foot-lambert (fL).

If you wish to determine color luminance, you can use a spectrophotometer. This device provides three-dimensional numeric values, or L*a*b color space, precisely defining an object’s color. The “L” in L*a*b stands for lightness value. This ranges from 100 — which is pure lightness — to -100, which is pure darkness.

Various factors aid in getting accurate luminance measurements, including the object's surface properties. Glossy surfaces will reflect the light, affecting luminance readings. The room's ambient light could also alter the readings. In some cases, you might need to control ambient light conditions or compensate for them in your analysis. Speak to a professional about how to optimize your lab's conditions for accurate readings.

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What Is Illuminance?

In a single sentence, the illuminance formula means how much luminous flux is spread over an area — it is the intensity of light falling onto a surface. Illuminance is a concept of photometry, represented by the amount of light received on a surface. Illuminance also relates to how humans perceive an illuminated area's brightness.

Illuminance measurements are usually used in fields such as photography, cinematography, architecture, and interior design. Occupational health and safety also use illuminance as a guideline to ensure that healthcare environments are adequately lit. A hospital hallway, for example, would need brighter lighting or luminous flux than an office where a person would read documents.

How to Measure Illuminance

Illuminance calculates the total amount of light a source puts out. This luminous flux is measured in lumens per square meter or lux (lm/m2) according to SI, or the U.S. measurement of foot-candles (lm/ft2). To determine how much light is falling onto a surface, professionals use an illuminance meter. By placing it in the area where the light is falling, they can determine the specific amount of lux.

As mentioned above, different applications output varying intensities of light. For example, public areas, family living rooms, and office building hallways can have a general measurement range of a few hundred lux, while full daylight outputs thousands of lux. Commercial and residential applications require various lux measurements for visual comfort, color rendering, or similar purposes.

A diagram showing how luminous flux, luminous intensity, and luminance relate

Measuring Light Interaction

Spectrophotometers determine the color of a sample by measuring transmitted or reflected light. These devices illuminate a sample using a light source and measure the amount of light absorbed, transmitted, or reflected at different wavelengths. You can use the color measurement results to analyze a material's physical properties through changes in color.

A few applications that use and benefit from this information include:

  • Chemical analysis: In the chemicals sector, a spectrophotometer can determine the clarity and color of liquid or powder chemicals, which assists with quality control measures.
  • Building products: In the construction sector, spectrophotometers can allow you to measure samples of materials like cement or roofing granules for color consistency and quality monitoring.
  • Pharmaceuticals: In the pharmaceutical industry, you can refine drug formulations and identify the concentrations of certain ingredients in medications.
  • Food and beverage industry: In the food and beverage sectors, you can use spectrophotometers to ensure color consistency across batches, appeal to consumer preferences, and uphold quality assurance.

Learn More About Color Measurement Devices With HunterLab

Receive advice and more information on illuminance and luminance from the HunterLab team. With over 70 years in the business, we are at the forefront of designing machines that give information about materials' chemical composition and physical properties based on their interactions with light.

Our first-class benchtop spectrophotometers ensure that you receive accurate color measurements. By understanding a color’s luminance value and other color-scale values, these advanced machines are the right tools for the job if you want to get the correct color data.

We have numerous types of spectrophotometers for different jobs. Businesses with production lines can benefit from our benchtop spectrophotometers, while professionals who need easily transportable devices — such as for quality control purposes across a facility — can select from a range of portable models. We also offer Quality Control (QC) software with every spectrophotometer and service, validation and compliance software.

Contact HunterLab today to learn more about measuring and working with color and lighting.