Lumen Calculator

Now compare various LED brightness and beam angles with one unit!


Those of you using LEDs for design and development know how frustrating it can be to look at specs for LEDs and get an idea of the total light output of the device.

Typically, manufacturers and vendors supply optical performance that lists among other data, the light output in mcd (milliCandellas). The spec also includes either the half angle or beam coverage angle produced by the LED's optical design. You may see one line statements from vendors that call out these two parameters as in " 25000 mcd at 10° " or " 1100 mcd at 120° ". How do you compare total light output emitted from the device?

Total light output is measured in Lumens, not candellas. Candellas are typically used to express brightness of point sources that emit light in a specific direction. Without going into a long discussion of steradians (the unit solid angle in a spherical shape), we've developed a simple calculator for you to calculate the approximate light output in Lumens. All you need to know is the candella output and the half angle (typically "Viewing Angle"/2) . Get this data from your spec sheet. Look at the radiation diagram displaying overall light output beam pattern. The diagram is typically symmetrical and the half angle is the point on one side where the beam crosses below 50% intensity.

This is an approximation of total light output in lumens when the half angle is defined by the angular value off axis where the output falls below 50% of max output. No attempt is made to account for the shape of the distribution pattern between 100% and 50% output.

Below is a chart that compares the Lumen output of a given LED die having various half angles. You can use this chart to compare a 1000 mcd LED having a 60° half angle with other LEDs having different beam intensities and different half angles. Notice that a 10° 35,000 mcd LED has nearly the same total Lumen output as the 1000 mcd 60° LED. Remember that half angle is one-half of the Viewing Angle.

Note that the Lumens put out by LEDs falls far short of regular incandescent bulbs. LEDs are 'point sources" while bulbs radiate light in almost all directions. A 4-Watt night light bulb delivers about 20 Lumens - in all directions. If it radiated light in one direction (assuming one steradian) it would deliver approximately 1.6 Lumens. See the Lumens chart below for some standard size incandescent light bulbs. Note that incandescant bulbs become more efficient as the size increases.

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