Why direct comparison of traditional lighting lumens (sodium, mercury, metal halide) with catalog lumens from LED lighting can not produce accurate findings.
The number of lumens listed in product catalogs cannot be used to compare LED lighting with conventional lighting since the amount of lumens that the human eye perceives depends on the type of lighting technology used. Three things account for this:
1. LED lighting provides a wider spectrum of light than traditional bulbs, which have a more limited one.
2. The variety in how the human eye responds to different levels of light is not taken into account by the usual methods for calculating lumen value.
3. The measurement of LED lights includes the full fixture and power supply system, whereas the measurement of luminous flux for conventional lamps only considers the light source.
1. LED lighting provides a wider spectrum of light than traditional bulbs, which have a more limited one.
The conventional approach to estimating a lamp's output light power makes no allowance for light reflection from objects. But in fact, depending on the color of the surface, things reflect light in different ways. For instance, if a yellow light is used to illuminate a green item, the whole light beam will be absorbed by the surface of the object, giving the thing a dark appearance. When a green object with this type of illumination is placed on a black surface, it becomes absolutely invisible. In reality, a little bit of a different effect results from light reflecting off of the actual things. For instance, grass seems green but really includes a variety of pigments (such as chlorophyll, carotenoids, xanthophylls, etc.), therefore when lighted by yellow light, it will reflect part of the light rays and appear gray.
Since sodium lamps used for street lighting have a limited light spectrum, they need to provide a lot of light in order to ensure adequate visibility. Similar to the sun's spectrum, LED lighting has a broad range of light. As a result, object color differences are more distinct, improving contrast and improving visibility in a given space. Therefore, LED lighting uses far less lumens while yet providing improved optical clarity.
2. The variety in how the human eye responds to different levels of light is not taken into account by the usual methods for calculating lumen value.
Rods and cones are the two primary categories of photoreceptors found in our eyes. Cones are capable of color vision (sometimes referred to as "photopic vision"), are sensitive to bright light, and function normally during the day. Rods nevertheless respond to light stimuli under challenging circumstances (with little light). This is referred to as scotopic vision (when a person perceives a colorless environment because the cones that detect color are dormant during night vision).
Only photopic vision is measured by photometers used to detect light intensity. However, in real-world situations, rods and cones (also known as "mesopic vision") will be used to process light. The S/P ratio is useful in this situation because it enables the conversion of conventional lumens into lumens that are really seen by the human eye.
The ratio of a light's blue-green to green-yellow hue is called S/P. A greater ratio value and improved visibility are both produced by a bigger proportion of blue-green colors. Higher S/P ratio light sources improve vision at lower light intensities.
The table provides an illustration of how to convert conventional lumens into lumens that the human eye can truly perceive. Due to its substantially increased efficiency, LED lighting offers enhanced visibility while using less energy.
3. The measurement of LED lights includes the full fixture and power supply system, whereas the measurement of luminous flux for conventional lamps only considers the light source itself.
At room temperature, the efficiency of conventional sodium, mercury, and metal halide discharge lamps is the sole factor considered. The effect of the socket in which the lamp is mounted is not considered in this method. High-pressure sodium lamps and some types of LED lighting may be highly efficient (up to 100 lumens per watt, for example). However, the energy efficiency ratio by itself does not reflect the actual quantity of light that a light source actually provides for a given use.
Efficiency of lighting should be evaluated in relation to the lamp in the fixture. Instead of measuring lumens output by a light, one should measure lumens that reach a final goal. Such a measurement of lighting efficiency will never match the lumens produced by the illumination source. The things that have an impact on the illumination put in the fixture are what cause the poorer efficiency:
Traditional lights emit light in all directions, which is known as trapped light. These lighting sources require sufficient mirrors within sockets that are made to reflect as much light as possible and focus it on the intended target. All of the light beams cannot be efficiently redirected, though.
- Protective lenses: Luminaires typically feature lenses that, in addition to serving a protective purpose, also aid in focusing light beams on the intended target. A portion of the light output is lost because the materials used to make lenses do not have 100% light permeability.
- Operating Temperature - In the case of temperature fluctuations, the performance of several light sources is decreased. At 25°C, the source efficiency is measured. However, especially for street lighting, the actual operating temperature differs greatly from the test temperature.
Power Source: The majority of light sources feature power supply that can change the input voltage to the lamp's specific voltage. Power supply damage might vary from 5% to 25%.
A further element that influences lighting's ultimate performance and is crucial for comparing LED lighting to conventional lighting is performance degradation over time. Traditional lighting sources, notably metal halide lamps, are characterized by considerable performance degradation even after brief use:
The service life of high pressure sodium lights is 24 000 hours, however they lose more than 30% of their original efficiency. Metal halide lamps have a service life of 6,000–15,000 hours and have an efficiency loss of up to 50%. With a service life of 50 000–100 000 hours, LED lighting suffers a 30% productivity reduction after 50 000 hours of use.
The aforementioned comparison demonstrates unequivocally that LED lighting provides superior performance over a considerably longer length of time than a traditional lighting source, allowing one to greatly delay the need to replace or repair the lighting.
Case study: In the state of Wisconsin in the United States, high-pressure sodium lights that were used in the school parking lot were replaced with LED bulbs that provided 8040 lumens. The previous lighting provided 19 000 lumens. Even though the area was illuminated with less lumens after the lighting upgrade, car park customers said the area was considerably better lit.
Compared to the region illuminated by high-pressure sodium lamps (19 000 lumens), the left side of the parking lot has LED lighting (8040 lumens), which offers superior visibility.
