Battery Equivalents and Replacements

Candela vs. Lumens: What Is The Difference?

Candelas and lumens are used to describe the performances of various light sources, making it very useful to know what they actually mean.

Both candelas and lumens are units of the International System of Units, and both refer to (simplified) the amount of light. However, ...

Published: September 27, 2022.

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 Candela And Lumens Defined

Simplified, candela (cd) measures the amount of light in a particular direction given by a light source, while lumens (lm) measure the total amount of light given by a light source.

"Particular direction" is a solid angle (also known as a spatial angle) given in steradians (sr) and labeled as Ω.

For example, a sphere features a solid angle of 4π sr (~12.56 sr), while a cone with a 60° angle features a solid angle of one steradian (1 sr).

Candela and Lumens Relation

The lumen (lm) is related to the candela (cd) and steradians (sr) as:

1 lm = 1 cd sr

Since a sphere has a solid angle of 4π sr (~12.56 sr), a light source that radiates 1 (one) candela of light in all directions features a total luminous flux of:

1 cd x 4π sr = ~12.56 cd sr = ~12.56 lm

Few Examples

Candle

An ordinary candle emits light with the luminous intensity of roughly 1 cd - hence the name "candela."

If that light is radiated in all directions uniformly, the light (luminous) flux is:

Φv = 1 cd * 12.56 sr = 12.56 lm

14W LED Bulb

14W LED bulbs are very often used in homes to replace old 100W incandescent bulbs and 25W fluorescent lights.

As such, they are able to provide a light output of ~1400-1700 lumens, depending on the model, light temperature, and similar.

If we assume that a 14W LED bulb provides 1500 lumens, then if the light is radiated in all directions, the intensity is:

Iv = 1500 lm / 12.56 sr = ~ 119.4 candela

If the light is focused in a 20° beam (0.095 sr), the light intensity is:

Iv = 1500 lm / 0.095 sr = ~ 15789 candela

So, depending on the beam angle, the very same 1500 lm provides the light intensity of ~119 and ~15789 candelas.

Candela, Lumens, and Wattages

The following comparison chart lists typical luminous flux (lumens) for various light sources and their electric power consumption (given in Watts):

Lumens Incandescent
(Tungsten)
Halogen
Incandescent
Fluorescent LED
90 15 6 2-3 1-2
 200  25   3-5  3-4
 450  40  29  9-11  5-8
 800  60    13-15  8-12
 1100  75  53  18-20  10-16
 1600  100  72  24-28  14-17
 2400  150    30-52  24-30
 3100  200    49-75  30-36
 4000  300    75-100  40-45

Note: These values change over time with technological advancements, especially for LED light sources. Also, they depend on the LED light color, if the light is dimmed and similar.

So, if You have a 1000 lumens LED flashlight, depending on the exact LED light source, You can expect a power requirement of 10-15 Watts from the flashlight's battery pack.


Long Story Short: Lumens is a measure of total light output, while candela is a measure of light intensity.

A LED flashlight, for example, with the variable zoom and variable LED output, can change zoom (increase or decrease the light intensity - candela) or can change the LED total light output (increase or decrease the total amount of light - lumens).