Lighting Calculator by Zonal Cavity Method (also known as the Lumen Method) is a common approach used in lighting design to calculate the number of luminaires (light fixtures) needed to achieve a desired illumination level in an indoor space. Here’s a detailed guide on how to use the Zonal Cavity Method for lighting calculations:
Steps for Using the Zonal Cavity Method
- Determine Room Characteristics:
- Room Dimensions: Measure the length (L), width (W), and height (H) of the room.
- Working Plane Height: The height above the floor where the lighting level is desired, typically the height of a desk or work surface.
- Calculate the Room Cavity Ratio (RCR): The RCR is a dimensionless number that describes the proportions of the room and affects how light is distributed. $$\text{RCR} = \frac{5 \times (\text{Room Height} – \text{Working Plane Height}) \times (\text{Room Length} + \text{Room Width})}{\text{Room Length} \times \text{Room Width}}$$
- Determine the Coefficients of Utilization (CU): The CU is a factor that indicates how effectively a luminaire delivers light to the working plane. It depends on the room and luminaire characteristics and is usually found in the luminaire manufacturer’s data tables.
- Determine the Light Loss Factors (LLF):
- Lamp Lumen Depreciation (LLD): Reduction in lamp output over time.Luminaire Dirt Depreciation (LDD): Reduction in output due to dirt accumulation.Other Factors: Other relevant factors based on the specific environment.
- Calculate the Total Initial Lumens Required: Based on the desired illuminance level (E) in lux (lm/m²) and the area of the room (A) in square meters. $$\text{Total Initial Lumens Required} = E \times A$$
- Calculate the Number of Luminaires Needed:
- Luminaire Lumens: The initial lumens output of one luminaire.
- Adjusted Lumens per Luminaire: $$\text{Adjusted Lumens per Luminaire} = \text{Luminaire Lumens} \times \text{CU} \times \text{LLF}$$ $$\text{Number of Luminaires} = \frac{\text{Total Initial Lumens Required}}{\text{Adjusted Lumens per Luminaire}}$$
Example Lighting Calculator
Let’s work through an example to illustrate these steps.
Room Characteristics:
- Length (L) = 10 meters
- Width (W) = 5 meters
- Height (H) = 3 meters
- Working Plane Height = 0.8 meters
- Desired Illuminance Level (E) = 500 lux
1: Calculate Room Cavity Ratio (RCR): $$\text{RCR} = \frac{5 \times (3 – 0.8) \times (10 + 5)}{10 \times 5} = \frac{5 \times 2.2 \times 15}{50} = \frac{165}{50} = 3.3$$
2: Determine Coefficient of Utilization (CU):
- Assume CU = 0.6 (from luminaire manufacturer’s data for a specific room and fixture type).
3: Determine Light Loss Factors (LLF):
- Lamp Lumen Depreciation (LLD) = 0.9
- Luminaire Dirt Depreciation (LDD) = 0.8
- Other Factors = 1.0
$$\text{LLF} = 0.9 \times 0.8 \times 1.0 = 0.72$$
4: Calculate Total Initial Lumens Required:
- Area (A) = 10 meters × 5 meters = 50 square meters
$$\text{Total Initial Lumens Required} = 500 \, \text{lux} \times 50 \, \text{m}^2 = 25,000 \, \text{lumens}$$
5: Calculate Adjusted Lumens per Luminaire:
- Assume each luminaire has an initial output of 3,000 lumens
$$\text{Adjusted Lumens per Luminaire} = 3,000 \, \text{lumens} \times 0.6 \times 0.72 = 1,296 \, \text{lumens}$$
6: Calculate the Number of Luminaires Needed: $$\text{Number of Luminaires} = \frac{25,000 \, \text{lumens}}{1,296 \, \text{lumens}} \approx 19.3$$
Since you can’t have a fraction of a luminaire, you would round up to the next whole number:
- Number of Luminaires Needed: 20 luminaires
Conclusion
Using Lighting Calculator Software by Zonal Cavity Method provides a systematic approach to lighting design, ensuring that the desired illumination levels are achieved effectively and efficiently. Always refer to manufacturer data for accurate CU values and ensure proper maintenance to account for LLF adjustments.
Lighting Calculator Software can be download below the link.
Note: All Password are [“salaimep” or “salaimep.com”]
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Also Download – Lighting Design Calculation Excel Download
