Understanding Lighting Calculation Methods

Lighting calculation methods are used to determine the required number and placement of light fixtures to achieve a desired level of illumination in a space. Different methods offer varying levels of accuracy and complexity, suited for different purposes.

Identifying Methods for Rough Calculation

The question asks which method is suitable for rough calculations and checking purposes. This implies a simple method that provides a quick estimate rather than a precise design.

• Watt per sq m method: This is a very basic method. It estimates the total power (in Watts) required for lighting based on the area of the space (in square meters) and a standard power density value (Watts per square meter) typically recommended for the type of activity in the space. This method does not consider room shape, surface reflectance, or specific fixture characteristics. Because of its simplicity and lack of detail, it is ideal for quick, rough estimates and preliminary checks.
• Point to point method: This method calculates the illuminance (light level) at specific points within a space. It uses the inverse square law and takes into account the intensity distribution of the light fixture, its mounting height, and the distance from the calculation point. This is a detailed and accurate method used for critical areas or specific task lighting, not for rough overall estimates.
• Lumen method: Also known as the zonal cavity method, this method calculates the average illuminance over an entire area. It considers the total light output (lumens) of the fixtures, the area of the space, and factors like room dimensions, surface reflectances, and fixture efficiency (represented by the Coefficient of Utilization - CU) and maintenance factors (MF). This method provides a more accurate average illuminance than the watt per sq m method but is still less detailed than the point-to-point method. It's used for general lighting design but is more involved than a rough check.
• Light flux illuminance method: This likely refers broadly to methods that use the total light output (flux) to determine illuminance, which is essentially what the Lumen method does. It is not a distinct simple method for rough checks.

Conclusion

Comparing the methods, the Watt per sq m method is the simplest and provides only a rough estimate of the required power based on area and a standard power density. This makes it suitable for initial estimations and checking if a design based on other methods is within a reasonable range. The other methods (Point to point and Lumen method) are more detailed and used for actual design calculations.

Therefore, the method used for rough calculations and checking purposes is the Watt per sq m method.