Coefficient of Utilization Calculator

| Added in Physics

What is Coefficient of Utilization?

The Coefficient of Utilization (CU) is a measure of the ratio of luminous flux that actually reaches the desired area compared to what's initially emitted by the fixture. It's a key metric in lighting design because it helps you understand how effectively your lights are being used.

Knowing your CU can save you from overspending on electricity and ensure your lighting is both effective and efficient.

How to Calculate Coefficient of Utilization

Calculating the Coefficient of Utilization requires two pieces of information:

  • The total luminous flux emitted by your fixture
  • The luminous flux that actually reaches the desired plane

The formula to calculate CU is:

[\text{CU} = \frac{\text{Luminous Flux Reaching Desired Plane}}{\text{Total Luminous Flux Emitted}}]

Where:

  • Luminous Flux Reaching Desired Plane is the amount of light that actually illuminates the target area (in lumens).
  • Total Luminous Flux Emitted is the total amount of light emitted by the fixture (in lumens).

Calculation Example

Step 1: Determine the total luminous flux emitted by your fixture. Let's say this is 6000 lumens.

Step 2: Measure the luminous flux reaching your desired plane. Suppose this value is 2400 lumens.

Step 3: Using the formula, calculate the CU.

[\text{CU} = \frac{2400}{6000} = 0.4]

The coefficient of utilization is 0.4, indicating that 40% of the emitted light is effectively reaching your desired area.

Why It Matters

A CU of 0.4 means 40% of the emitted light is reaching the desired plane. The higher this value, the more efficient your lighting fixture is.

Key Takeaways:

  • A high CU value indicates efficient lighting.
  • A low CU means you might need to rethink your lighting setup to avoid inefficiencies and higher costs.

Summary Table

Parameter Value
Total Luminous Flux Emitted 6000 lumens
Luminous Flux Reaching Desired Plane 2400 lumens
Coefficient of Utilization (CU) 0.4

Frequently Asked Questions

A good CU typically ranges from 0.4 to 0.8 depending on the room conditions. Values above 0.6 are generally considered efficient for most indoor applications.

Several factors affect CU including room geometry (length, width, height), surface reflectances (walls, ceiling, floor), fixture type and mounting height, and the presence of obstructions.

The CU helps you understand how effectively your lighting fixtures illuminate the work plane. A higher CU means less wasted light and lower energy costs for the same illumination level.

You can improve CU by using lighter colored room surfaces, choosing appropriate fixture types for your space, optimizing mounting heights, and selecting fixtures with better light distribution characteristics.