Lighting terminology 

1:16 1:16

F 1:34 1:34

Hi Faisal, we're glad to hear you like the video :)

Lumen = luminous flux per unit solid angle. Candela = lumen per area.

I think the confusion arises from this: While the candle is visible from every direction, the light source's intensity (candela) measures the brightness of the beam in a particular direction. This measurement is only concerned with a limited area of the imaginary sphere that surrounds the candle. In order to avoid even more confusion introduced by the term steradian, think about it as a limited surface area of a sphere that is bordered by a circle. The total surface area of a sphere is made up of roughly 12.57 steradians. Conversely, one steradian is somewhere between 1/13th and 1/12th of the total surface of the sphere. For a simplified illustration of this phenomenon, the presenter used a frame in this video (1:10). Now, back to the candela. At one point in history humanity agreed that the intensity of the light that a "standard" candle emits in the mentioned direction (one steradian) would be identified as one candela. Which is nice, but we also wanted to determine another practical measure, the total quantity of visible light, flowing from the light source, aka the luminous flux or luminous power. For the utter confusion of future students the measure of luminous power or luminous flux - called lumen - was defined in relation to the luminous intensity, candela. It was said that if the light source's intensity is one candela, then the amount of light flowing in the direction of one steradian would be identified as one lumen. Hence, the total quantity of light emitted by the candle equals 12.57 lumen, the number of steradians in the entire sphere around the candle. (see at 1:19 in the video) On one hand it is pretty obvious that there is a strong correlation between the intensity of a light source and the total amount of light it emits in a certain direction, but on the other hand this circular reference between candela and lumen can easily create confusion. One might look at it as multiple aspects of the very same thing. In layman’s terms both candela and lumen are concerned with the amount of light, but while candela refers to the intensity of the light source, lumens refer to the total amount of light flowing from it. The intensity of a "standard" candle is one candela which generates one lumen of light flow for each steradian, a 12.57 lumens in total.

samelorc

Hi there and thanks for reaching out. We do not carry out lighting calculations on request like these, but we do provide guidance in other videos. Please view philips.to/2zUzAYR and philips.to/2zUzCzX. Alternatively you can select products from our online product catalog and download the data (photometrics) from there. Many thanks.

You may check these videos for more detailed explaination Lighting design Terminology Part-1 ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Q01uPxPdDy8.html Indoor Lighting Design Part -2 ( you can learn how to calculate the number of luminaries and factors that to accounted to calculate the same) ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-B9hJCABFZy4.html

You may check these videos for more detailed explaination Lighting design Terminology Part-1 ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Q01uPxPdDy8.html Indoor Lighting Design Part -2 ( you can learn how to calculate the number of luminaries and factors that to accounted to calculate the same) ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-B9hJCABFZy4.html

Hi Matheus, thanks for getting in touch. It would be great if you could fill in our online contact form and a member of our consumer care team will be able to assist you further: philips.to/2HL0KHS. Thanks!

Hey Eva, luminous distribution angle describes the spread of light from a lamp or luminaire. Beam angle is the angle at which intensity is 50% of maximum x 2 (each side of the maximum). Hope this helps!

Hi there, thanks for reaching out. Unfortunately, this is not something we can assist you with. We'd suggest the use of a brightness tester. Thank you!

12.57 is 4*pi. A point source with a luminous intensity of 1 candela emits lights at lumen for each steradian (solid angle). Because a sphere is made of 4*pi steradians, this means that the point source emits a total of 4*pi (=12.57) lumens in all directions.

@@momhn4283 thanks mate!! that makes sense.

Very good

haha yes! get with the metric system already!