With a visual representation of the units, perhaps it is more intuitive to understand the different units of measure. If someone says, "I want the intensity of the surface to be 100W/m²", we need to be clear if they mean illuminance, or if they mean W/sr.īelow is a schematic image of the above photometric units. Different people have different definitions for what intensity (among other optical terms) means, so when we are talking to non-optical people, it is critical to make sure that the optical requirements are precise. We don't want to start setting up our system for illuminance when the required target performance is the intensity. We want to be able to define these units correctly when we start the design, because a seemingly small error here will change everything. *Please note that the designations of Φ, E, I, L are not universal, and sometimes P, H, J, and N are used for the corresponding radiometric quantities, while F, E, I, and B are used for the corresponding photometric quantities. In this case, it is good practice to call the radiant flux the total radiant flux to distinguish between the spectral dimension and the total spectral range. The radiometric quantities can be further decomposed to spectral flux, spectral irradiance, spectral intensity, and spectral irradiance if the radiometric values are different in the spectral dimension of wavelength. The terms may be confusing at first, but to summarize, the radiometric quantities are radiant flux Φ, irradiance E, radiant intensity I, and radiance L, while the photometric quantities are luminous flux Φ, illuminance E, luminous intensity I, and luminance L. On the other hand, it is vital to balance the energy of the light source with sub-UV blue light and near-IR red light as the human eye is most sensitive at about 550nm and will require more light on both sides of the spectrum of 550nm to achieve a balance for the human eye. For example, a laser diode with a wavelength of 905nm cannot be viewed by the human eye, and therefore, any photopic measurements always zero. The distinction between these two units is essential when we are considering our illumination system. While radiometry is the measurement of electromagnetic radiation, including the visible light spectrum, photometry measures the response of the human eye to light. There are two aspects to the unit of measure of an illumination system: radiometric quantities and photometric quantities. There are two groups of the unit of measure, and subsets of measurement for each. The units of measure of an illumination systemīefore diving into the core of the performance, let's define the parameters of our illumination system. The detector can be any shape imaginable. Although common optical engineering properties such as color, cost, and ease of manufacture apply in this article, we will define the standard illumination requirements for various systems. With the lessons from this article, we will be able to define the critical parameters for our illumination system, and ensure that our illumination design is a good one. Some constraints make optimal transfer change depending on what we prioritize, such as size and performance. However, we know that things aren't that simple. There is a multitude of methods to transfer the light. "The optimal transfer of the light source to the detector" What makes a good illumination design?Īt the core of illumination design, there is only one goal for the performance: The question of "What makes a good illumination design?" will be unravled through the units and targets that are common in illumination design. This lessonprovides a discussion and examples off the performance goals of illumination systems. In this lesson, the various targets for the illumination system will be described so that you can clearly define the target parameters of your illumination design. This lesson is part of the Illumination Systems Fundamentals Learning Path. Questions like "What makes a good illumination design?" will be addressed. This lesson provides the fundamentals of illumination systems, in particular, the performance goals of illumination systems. This article is part of the Illumination Systems Fundamentals free tutorial.
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