Light Output Ratio (LOR) is a crucial factor to consider when choosing a lighting fixture. It determines the performance level of the fixture and indicates how much light is lost within it.
The Light Output Ratio (LOR) is a measure used to describe the efficiency of a luminaire (or a lighting fixture).
Calculation of Light Output Ratio
LOR is calculated by dividing the total light output of the lighting fixture by the light flux inside the lamp. This ratio is expressed as a percentage and indicates the efficiency of the fixture.
LOR = (Actual Lumen Output/Initial Lumens from LED) x 100
For instance, if an LED has an initial lumen rating of 1000 lumens, but when placed inside a luminaire, only 850 lumens are emitted due to losses (like absorption or reflection), then:
This would mean that the luminaire is 85% efficient at transmitting the light produced by the LED. The other 15% is lost within the luminaire due to various reasons (reflection, absorption, diffraction, etc.).
A higher LOR value means better performance, more light, and energy savings.
Light Output Ratio Calculator
Factors Affecting Light Output Ratio
Light produced inside a bulb exits in all directions except for its screwed base. When a bulb is inserted into a chandelier, lamp shade, or table lamp, some of the light coming from different directions will be lost, even if the reflective surface is perfect. LED lighting fixtures have higher LOR values because they are directional lighting sources, and light loss is minimal.
Measurement of Light Output Ratio
The LOR value of a lighting fixture is measured using an Ulbricht sphere or goniophotometer. A lamp with a certain brightness is mounted on the fixture, and the total lumen of the fixture is recorded. The total lumen is then divided by the lamp’s lumen to obtain the LOR value. If the brightness of the lamp is unknown, it should be measured using the same technique.
Importance of Light Output Ratio
Ignoring the LOR value during the design phase can lead to a dimmer environment than expected at the end of the application. Having knowledge about the LOR value helps obtain more realistic results. Photometric data of the fixture (IES, LDT) can provide information about the LOR percentage.
Misconceptions About Light Output Ratio
Some manufacturers claim that their lighting fixtures have 100% LOR value, but it is technically impossible. Even with a perfectly reflective surface, the light will always be lost.
LOR is an essential factor to consider when choosing a lighting fixture. It determines the fixture’s performance level and indicates how much light is lost within it. LOR values can be measured using an Ulbricht sphere or goniophotometer, and photometric data can provide information about the LOR percentage. Understanding LOR values helps obtain more realistic results and prevent a dimmer environment than expected.