Question

How do you calculate the thermal output of an LED?

Answer 1

To calculate the thermal output of an LED, you need to understand how much heat is generated by the LED based on its electrical power consumption and its efficiency. Here’s a simple way to do it:

1. Determine the Electrical Power Input:

   This is the amount of electrical power supplied to the LED. You can calculate it using the formula:
   
   \[
   P_{\text{in}} = V_{\text{LED}} \times I_{\text{LED}}
   \]
   
   - \(P_{\text{in}}\) is the electrical power input (in watts, W).
   - \(V_{\text{LED}}\) is the forward voltage of the LED (in volts, V).
   - \(I_{\text{LED}}\) is the current supplied to the LED (in amperes, A).

2. Determine the LED's Efficiency:

   LEDs are not 100% efficient at converting electrical energy into light. The rest of the energy is converted into heat. The efficiency of an LED is usually given as a percentage (you can find this in the datasheet, usually referred to as "luminous efficiency" or "electrical efficiency").

   If the efficiency is not provided, a typical LED might be 20-30% efficient, but this can vary depending on the type of LED.

3. Calculate the Thermal Output:

   The thermal output is the energy that is not converted into light, so it’s the energy lost as heat. You can calculate it as:

   \[
   P_{\text{thermal}} = P_{\text{in}} \times (1 - \text{Efficiency})
   \]

   - \(P_{\text{thermal}}\) is the thermal power output (in watts, W).
   - Efficiency should be in decimal form (for example, 30% efficiency = 0.30).

Example:

Let’s say you have an LED with the following characteristics:

1. Forward voltage (\(V_{\text{LED}}\)): 3.5 V
   

1. Current (\(I_{\text{LED}}\)): 0.02 A
   

1. Efficiency: 25% (0.25 in decimal form)
   

First, calculate the electrical power input:

\[
P_{\text{in}} = 3.5 \, \text{V} \times 0.02 \, \text{A} = 0.07 \, \text{W}
\]

Then, calculate the thermal output:

\[
P_{\text{thermal}} = 0.07 \, \text{W} \times (1 - 0.25) = 0.07 \, \text{W} \times 0.75 = 0.0525 \, \text{W}
\]

So, the thermal output (heat generated) by the LED is 0.0525 W.

Conclusion:

The heat output of the LED is determined by the difference between the electrical power supplied to the LED and the amount that is converted into light. The remaining energy is dissipated as heat.