Does a point light source exist or is it just an approximation of a light source viewed from very far away?
weiji-li
Does anyone know why the candela not the lm is being adopted as one of the seven SI base units? It seems that the other six SI base units are all very fundamental measurements but I am not sure why candela not luminance is the most fundamental measurements for light
ShaamerKumar
I think it is because our perception of light is not linear - a small change in intensity can be perceived as a much larger change in brightness.
I think the adoption of the candela as a base unit reflects the importance of considering our perception of light when making measurements.
sha-moose
I agree with @ShaamerKumar here. Light perception is highly dependent on perception, and lumens do not take that into to effect (rather, it's like an integration over all of the perspectives). On the other hand, the candela measures light we can see, coming directly from a source we can see, straight into our eyes. Plus, it's easier to measure too, and the folks who define the SI system tend to like consistency :)
rishiarjun
In reference to the conversation above, a lumen is mainly the total light amount that's emitted by a source. Candela in contrast is the amount of light in a particular direction. It is easier for a human to understand candela more since perception is easier to register to the eye, which candela takes more into account than lumen does. Let's compare a torch vs a bulb. A torch will have a high candela value since its light source is concentrated in single point and in one direction. A bulb, in contrast, has a high lumens value since it is spreading light over a much larger area than a torch.
jeeyookim
It's interesting to know that candela takes into account the direction of the light source, making it more perceptible to the human eye. This knowledge is particularly important for lighting designers and engineers who need to understand how to provide the right amount of illumination for a given space or task. By taking into account both the lumens and candela values of a light source, they can design lighting systems that are efficient, effective, and comfortable for users. It's also important to note that the color temperature and color rendering index (CRI) of a light source can impact how we perceive the illumination. For instance, a warm-colored light may be more suitable for creating a cozy atmosphere in a residential setting, while a cool-colored light may be more appropriate for a commercial or industrial application where visibility and productivity are essential.
Zc0in
@SeanW0823 A point light source is idealized as a point source of mass. Point light source is an abstracted physical concept, in order to simplify the study of physical problems. Just like the usual smooth plane, mass, no air resistance, point light source in reality does not exist, refers to a point from a point to the surrounding space uniform light source.
Does a point light source exist or is it just an approximation of a light source viewed from very far away?
Does anyone know why the candela not the lm is being adopted as one of the seven SI base units? It seems that the other six SI base units are all very fundamental measurements but I am not sure why candela not luminance is the most fundamental measurements for light
I think it is because our perception of light is not linear - a small change in intensity can be perceived as a much larger change in brightness.
I think the adoption of the candela as a base unit reflects the importance of considering our perception of light when making measurements.
I agree with @ShaamerKumar here. Light perception is highly dependent on perception, and lumens do not take that into to effect (rather, it's like an integration over all of the perspectives). On the other hand, the candela measures light we can see, coming directly from a source we can see, straight into our eyes. Plus, it's easier to measure too, and the folks who define the SI system tend to like consistency :)
In reference to the conversation above, a lumen is mainly the total light amount that's emitted by a source. Candela in contrast is the amount of light in a particular direction. It is easier for a human to understand candela more since perception is easier to register to the eye, which candela takes more into account than lumen does. Let's compare a torch vs a bulb. A torch will have a high candela value since its light source is concentrated in single point and in one direction. A bulb, in contrast, has a high lumens value since it is spreading light over a much larger area than a torch.
It's interesting to know that candela takes into account the direction of the light source, making it more perceptible to the human eye. This knowledge is particularly important for lighting designers and engineers who need to understand how to provide the right amount of illumination for a given space or task. By taking into account both the lumens and candela values of a light source, they can design lighting systems that are efficient, effective, and comfortable for users. It's also important to note that the color temperature and color rendering index (CRI) of a light source can impact how we perceive the illumination. For instance, a warm-colored light may be more suitable for creating a cozy atmosphere in a residential setting, while a cool-colored light may be more appropriate for a commercial or industrial application where visibility and productivity are essential.
@SeanW0823 A point light source is idealized as a point source of mass. Point light source is an abstracted physical concept, in order to simplify the study of physical problems. Just like the usual smooth plane, mass, no air resistance, point light source in reality does not exist, refers to a point from a point to the surrounding space uniform light source.