Doug Kerr
Well-known member
In technical articles, we commonly see the “potency” of a light beam at a certain place in its travels quantified as the illuminance of the beam there.
But that is not apt. Illuminance is not a property of a beam of light at some place in its travels. It is a measure of the illumination afforded by a beam of light on some surface, having a certain orientation, at such a place.
What does properly characterize the “potency” of a beam of light at a certain place is its luminous flux density. Yet we almost never see that quantity mentioned. Luminous flux density and illuminance have very similar definitions, and are closely related, so it is perhaps understandable that authors get them confused.
I sort this out (hopefully) in a new technical article on The Pumpkin, "Luminous flux density: the rarely mentioned photometric quantity".
This is a link to its listing on The Pumpkin index page:
Best regards,
Doug
But that is not apt. Illuminance is not a property of a beam of light at some place in its travels. It is a measure of the illumination afforded by a beam of light on some surface, having a certain orientation, at such a place.
What does properly characterize the “potency” of a beam of light at a certain place is its luminous flux density. Yet we almost never see that quantity mentioned. Luminous flux density and illuminance have very similar definitions, and are closely related, so it is perhaps understandable that authors get them confused.
I sort this out (hopefully) in a new technical article on The Pumpkin, "Luminous flux density: the rarely mentioned photometric quantity".
This is a link to its listing on The Pumpkin index page:
Best regards,
Doug