How to Measure Light: Tools and Techniques for Optimal Lighting

Human vision is remarkable, capable of detecting a wide range of light intensities. Yet, as light levels decrease, our ability to perceive fine details also diminishes. That’s why accurately measuring light is essential to create lighting environments that enhance functionality and aesthetic appeal. Here are some insights on how to measure light effectively to achieve the best illumination for your space.

Understanding Light

Before delving into measurement techniques, let’s briefly define what light is. At its core, light is a form of electromagnetic radiation that interacts with the human eye to create visual perception. It travels in waves and transfers energy, making it visible only when it interacts with a medium.

The Visible Light Spectrum

Light visible to the human eye falls within a specific range of the electromagnetic spectrum, between wavelengths of 380 to 750 nanometers. Beyond this range, we encounter forms of light such as ultraviolet and infrared, which are invisible to us but still affect our environment.

The Composition of White Light

In the late 1600s, Isaac Newton demonstrated that what we perceive as white light is, in fact, a blend of different colors. By passing sunlight through a prism, he revealed a spectrum of colors that combine to create white light. The visible spectrum includes the following colors:

• Red: 780-618 nm
• Orange: 618-581 nm
• Yellow: 581-570 nm
• Green: 570-497 nm
• Cyan: 497-476 nm
• Blue: 476-427 nm
• Violet: 427-380 nm

This understanding of light’s composition is key to optimizing lighting design, as it allows us to tailor color temperature and intensity to suit the intended purpose of a space.

Measuring Light: Key Units

When we talk about measuring light, we refer to the amount of energy emitted by a light source and how it interacts with the surrounding space. There are three primary units of measurement for light in the International System of Units (SI), each capturing a different aspect of illumination:

• Lumen (lm): Measures the total visible light emitted by a source.
• Lux (lx): Quantifies how much light reaches a surface, where one lux equals one lumen per square meter.
• Candela (cd): Focuses on the intensity of light in a specific direction, measured as lumens per steradian.

Luxmeters: Precision Tools for Measuring Light

A luxmeter is a device designed to measure the intensity of light in a given area. It is particularly useful for assessing whether lighting levels meet the required standards for different environments, from workspaces to residential areas.

How to Use a Luxmeter

Measuring light with a luxmeter is straightforward, but precision is key to obtaining accurate results. Follow these steps:

1. Positioning the Photoreceptor: Ensure that the luxmeter’s sensor faces the light source directly.
2. Selecting the Correct Scale: Choose the appropriate scale based on the strength of the light being measured.
3. Taking the Reading: After turning on the luxmeter, wait for the reading to stabilize on the screen.
4. Calculating the Final Value: Multiply the displayed reading by the selected scale to obtain the final lux measurement.

The 3 units of measurement of illumination

• Lumen (Lm): A lumen is the amount of visible energy that we can actually measure. It is the luminous flux of monochromatic radiation characterised by a frequency of 540x1012 hz and a radiant energy flux of 1/683 watts.
• Lux (Lx): one lux is the equivalent of the energy produced by one lumen incident on a surface of 1 m2.
• Candela (Cd): is the basic unit that measures luminous intensity. One candela is equivalent to 1 lumen per steradian (lm/sr). It is defined as the luminous intensity going in a specific direction, and is therefore related to the angle of aperture towards the light.

By understanding how light is measured and employing a luxmeter, you can create spaces that balance functionality with ambiance, ensuring your lighting design meets the specific needs of your environment.