Understanding Lighting Calculations: A Comprehensive Guide

Lighting calculations are an important aspect of any lighting design project, whether it is a residential space, commercial building or outdoor area. They involve determining the appropriate amount of light needed to meet specific requirements, taking into account factors such as the size of the space, its purpose and the desired atmosphere. This guide provides a comprehensive introduction to lighting calculations, covering basic concepts, methods, and practical applications.

• Illuminance (E): Measured in lux (lx), illuminance refers to the amount of light falling on a surface. It's a crucial factor in determining the overall brightness of a space.
• Luminous Flux (Φ): Expressed in lumens (lm), luminous flux represents the total amount of light emitted by a light source.
• Luminous Intensity (I): Measured in candelas (cd), luminous intensity describes the light emitted in a specific direction.
• Light Output Ratio (LOR): This factor accounts for the efficiency of a luminaire in converting electrical power into visible light. It's typically expressed as a percentage.
• Space-to-Height Ratio (SHR): This ratio determines the spacing between luminaires and their distance from the floor.
• Coefficient of Utilization (CU): This value represents the fraction of the total light emitted by a luminaire that reaches the working plane.
• Maintenance Factor (MF): The maintenance factor considers the gradual decrease in light output over time due to factors like dirt accumulation and lamp aging.

There are two primary methods used for lighting calculations:

The lumen method is the most common approach for calculating lighting requirements. It involves the following steps:

1. Determine the required illuminance (E): This value depends on the specific task or activity being performed in the space. For instance, reading requires higher illuminance than general ambient lighting.
2. Calculate the total area (A) to be illuminated: This includes the floor area and any other surfaces that need illumination.
3. Determine the light output ratio (LOR) and coefficient of utilization (CU): These factors depend on the luminaires and the room's geometry.
4. Estimate the maintenance factor (MF): This factor is typically set to 0.7 to 0.8 for most applications.
5. Calculate the total luminous flux (Φ) needed using the formula:

Φ = (E x A) / (LOR x CU x MF)

1. Select luminaires with the appropriate lumen output: Choose luminaires that can provide the calculated luminous flux.
2. Determine the number of luminaires required: Divide the total luminous flux needed by the luminous flux output of each luminaire.

The point-by-point method is more complex but offers greater accuracy, especially for irregularly shaped spaces or complex lighting arrangements. It involves calculating the illuminance at specific points within the space based on the location and orientation of light sources. This method typically involves the use of specialized software or spreadsheets to perform the calculations.

• Space Type: Different types of spaces, such as offices, retail stores, and residential areas, have varying lighting requirements.
• Task Type: The specific task being performed in a space influences the required illuminance level. For example, a library requires higher illuminance for reading than a hallway.
• Ceiling Height: Higher ceilings necessitate more powerful luminaires or a greater number of fixtures to achieve the desired illuminance.
• Room Reflectance: Light reflection from walls, ceiling, and floors affects the overall illuminance levels. Lighter colors reflect more light, resulting in brighter spaces.
• Luminaire Type: The type of luminaire used significantly affects light distribution and efficiency.
• Lamp Type: Different lamp types, such as incandescent, fluorescent, and LED, have varying light output, energy efficiency, and color temperature.

• Energy Efficiency: Proper lighting calculations help minimize energy consumption by selecting the right number and types of luminaires.
• Visual Comfort: Accurate calculations ensure appropriate lighting levels for different tasks and activities, contributing to visual comfort and productivity.
• Safety: Adequate lighting is crucial for safety, reducing accidents and improving visibility in workspaces and public areas.
• Aesthetics: Lighting plays a vital role in creating the desired ambiance and enhancing the architectural features of a space.