Pupil Lumens, PLM, lumen, unit light, unit light, measure, perception, eye, vision, photoepic vision, scotopic vision, retina, cones and rods, day vision, night vision

PLM – Pupil Lumens

THE NEW UNIT AND ITS MEANING

How do you compare different light sources? This is not so easy, because the human eye already perceives light differently. There are 2 basic types of vision and both should be taken into account when specifying brightness. The “photopic vision” and the “scotopic vision”. This is where a new unit comes into play, the pupil lumens (Plm).

Pupil Lumens, PLM, Lumen, Einheit Licht, Lichteinheit, messen, Wahrnehmung, Auge, Sehen, photoepisches Sehen, skotopisches Sehen, Netzhaut, Zapfen und Stäbchen, Tagsehen, Nachtsehen

 

THE PHOTOPIC VISION

Also called “day viewing” and is responsible for colour vision. Here the cones play the main role, the receptor cells in the eye that absorb different wavelengths of light. They provide high-contrast, colourful vision. We have 3 different types of these:

S-type (blue receptor; is most sensitive).

L-type (red receptor; is least sensitive)

M-type (green; is in the middle)

 

THE SCOTOPIC VISION

So-called “night vision” is made possible by the second type of light-sensitive cells, the rods. They far outnumber the cones and are responsible for perceiving brightness and contrast. They also react to very weak light at the edge of the retina. However, vision at night is usually blurred and colourless. The saying “all cats are grey at night” is no coincidence.

Most people use photopic and scotopic vision at the same time and this leads to the fact that light with a high blue component (cold white) is perceived as brighter and more intense than light with a higher red component. We remember: the blue receptors are more sensitive than the others.

 

Pupil Lumens, PLM, Lumen, Einheit Licht, Lichteinheit, messen, Wahrnehmung, Auge, Sehen, photoepisches Sehen, skotopisches Sehen, Netzhaut, Zapfen und Stäbchen, Tagsehen, Nachtsehen

 

The unit of luminous flux “lumen” indicates the measured brightness of a lamp, but does not take into account the colour perception properties of the human eye. It merely indicates the total amount of light emitted by a lamp.

The pupil lumen (Plm) now indicates much more precisely how bright a lamp is perceived. With LED lamps, the change in colour is limited by the colour rendering index. This should be in the range Ra > 80. For private use, therefore, it is sufficient to indicate the lumens because the colour of the light cannot change to such an extent that it has such a great influence.

For industrial and outdoor applications, however, there are new ways and means. With much lower energy consumption and effort, the Plm specification can be used to illuminate much more effectively. For example, in street lighting. A cool-white street lamp is perceived as much brighter than a yellowish one, less energy is consumed, and it may even be necessary to install fewer of them.

 

Pupil Lumens, PLM, Lumen, Einheit Licht, Lichteinheit, messen, Wahrnehmung, Auge, Sehen, photoepisches Sehen, skotopisches Sehen, Netzhaut, Zapfen und Stäbchen, Tagsehen, Nachtsehen

 

CALCULATION OF THE PLM – PUPIL LUMENS

The calculation is based on a fixed formula and, depending on the type and condition of the lamp, a so-called correction factor is added that takes into account the relationship between photopic and scotopic vision: the P/S factor. Logically, it varies from lamp to lamp, depending on the manufacturer, type and product.

Plm/Watt = Lm/Watt * P/S

A few examples in a table to illustrate.

The correction factors were determined by the Lawrence Berkley Laboratory (LBL):

Illuminant Lm/Watt Lm P/S Plm
Incandescent lamp 100 watt
warm white
15 1500 1,26 1890
Fluorescent tube
58 watt
65 3770 0,98 3695
Halogen 50 watt
neutral white
21-23 1050 1,32 1386
LED 25 watt
cold white
85-100 2500 1,9 4750

 

Our perception is always made up of different factors and is also subjective. Some people are very sensitive to light, others perceive colours completely differently. Therefore, there is no value that is correct for everyone and reflects what the individual perceives.

 

Human and light, LED, LED knowledge, LED light colour, LED Technology, Light Sources, Lumen, measure light, PLM, Pupil Lumens

Leave a Reply

Your email address will not be published. Required fields are marked *

Stay up to date

Subscribe to our newsletter now and receive exclusive information on articles, offers and events.