If the light is radiated equally in all directions, it will have an intensity of approx 135 candela. Candela takes the spread of light into account but lumens do not.įor example, A 25 W CFL bulb outputs around 1700 lumens. Simply put, candela measures the amount of light emitted in a particular direction, whereas lumens measure the total amount of light emitted in all directions. So what’s the difference and why knowing the difference is important? Candela measures the luminous intensity, while lumens measure the luminous flux. Lumens vs CandelaĬandela and lumens measure two different aspects of lighting.
The term foot-candle is commonly used in the US, whereas the rest of the world uses the term lux. One foot-candle is defined as one lumen per square foot. What Is Foot-candleįoot-candle (abbreviated: fc) is a non-SI unit of illuminance, which is the luminous flux per unit area. If you use the same 1000 lumens bulb to light up a small 10 m2 room and a large 20 m2 room, the ground(surface) of the small room will look brighter because it has a higher lux value of 100 lux whereas the large room has only 50 lux.
Simply put, lux is used to measure the intensity of visible light that illuminates a surface. One lux is defined as one lumen per square meter. Lux (symbol: lx) is the unit of illuminance, which is the luminous flux per unit area. However, candlepower is still used to specifically describe the luminous intensity of all sorts of narrow-beamed lights such as high-powered flashlights and spotlights, because candlepower measures the intensity of light on a target rather than the total amount, which is a more accurate measure in this condition. Candlepower is a largely obsolete term now and has been replaced by candela. What Is CandlepowerĬandlepower(abbreviated: cb) is a unit of luminous intensity. Simply think of the steradian(solid angle) roughly as a particular direction, so it’s easy to understand candela means how much light a light source can emit in a particular direction. Given the definition, 1 cd = 1 lm / 1sr, which means candela equals luminous flux per unit solid angle. A solid angle is expressed in a dimensionless unit called a steradian (symbol: sr). Candela measures luminous power per unit solid angle emitted by a light source in a particular direction. What Is CandelaĬandela (symbol: cd) is the unit of luminous intensity in a given direction. The higher lumens, the brighter the light source looks to human eyes. Simply put, the lumens mean how much light a light source can emit in all directions. Lumen(symbol: lm) is the unit of luminous flux, a measure of the total quantity of visible light emitted by a source per unit of time. As FTC has assigned an unconventional meaning to brightness when applied to lamps and bulbs, brightness means luminous flux in the context of light bulbs and lamps. Brightness: Although the original meaning of “brightness” is Luminance.The unit of illuminance is lux, with the symbol lx (= lm/m2) Illuminance: A measure of total luminous flux illuminates onto a surface.The unit of luminous intensity is candela, with the symbol cd (= lm/sr). Luminous Intensity: A measure of luminous power emitted by a light source in a particular direction.The unit of luminous flux is lumen, with the symbol lm (= cd⋅sr). Luminous Flux: A measure of the total amount of visible light a light source emits.A quick look at the simplified explanation will help you easily understand the relationships between lumens, lux, and candela. Here are some common terms we’ll frequently mention in the article. Here are explanations and comparisons of the common terms you’ll see related to how bright a light source looks in various situations. What do these terminologies mean? What’s the difference and which term to actually look for when choosing your ideal light source? When shopping for bulbs and lamps for our home lighting designs, we often see these different terms labeled on the package and mentioned by manufacturers – Lumens, lux, candela, foot-candle, and sometimes candlepower.
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