LEDs, or light emitting diodes, have become increasingly popular over the past few decades as an energy efficient and long-lasting light source. But not all LEDs are created equal – the color of the LED affects how bright it appears. In this article, we’ll explore which LED color produces the brightest light.
How LEDs Produce Light
LEDs produce light through a process called electroluminescence. When current passes through the LED, it excites electrons in the semiconductor material used in the LED. As the excited electrons return to their ground state, they emit photons of light.
The color of light emitted depends on the semiconductor material used in the LED. Some common materials used and the color light they emit are:
|Gallium arsenide phosphide
|Gallium nitride + Indium gallium nitride
By combining red, green, and blue LEDs, any color can be produced, including white light.
Luminous Efficacy of LED Colors
One way to compare the brightness of different colored LEDs is to look at their luminous efficacy. Luminous efficacy measures how well a light source produces visible light. It’s expressed in lumens per watt (lm/W). The higher the luminous efficacy, the more light produced per unit of electricity.
Here are typical luminous efficacies for different colored LEDs:
|Luminous Efficacy (lm/W)
From this data, we can see that green LEDs have the highest luminous efficacy, meaning they produce the most light for each watt of electricity. Blue LEDs have the lowest luminous efficacy.
However, luminous efficacy doesn’t tell the whole story. The human eye perceives brightness differently at different wavelengths. So even though blue LEDs produce fewer lumens per watt, they may still appear bright to the human eye.
To account for the eye’s wavelength sensitivity, we can look at the luminosity function. This shows the eye’s perceived brightness at different wavelengths of visible light.
Here is a graph of the luminosity function:
The yellow part of the visible spectrum around 555 nm corresponds to the peak sensitivity of the human eye. We perceive these wavelengths as brighter than other colors. The blue and red parts of the spectrum near the edges are less bright to our eyes.
This means an LED producing yellowish-green light near 555 nm will appear brighter than a blue or red LED, even if they have similar luminous efficacy values.
Another consideration is the LED’s luminous intensity. This measures the amount of visible light emitted by the LED in a particular direction, measured in candela (cd).
Luminous intensity takes into account the luminosity function, so it represents how bright the LED appears to the human eye.
Here are typical luminous intensities for different colored LEDs:
|Luminous Intensity (cd)
From the luminous intensity measurements, we see that green LEDs produce a substantially brighter output compared to red or blue LEDs.
Perception of Brightness
Although measurements like luminous efficacy and intensity give insights into LED performance, human perception of brightness is also important. There are a few factors that influence how bright different LED colors appear to our eyes:
– Wavelength sensitivity – As shown in the luminosity function, eyes are most sensitive to green-yellow light near 555 nm.
– Surrounding conditions – LEDs viewed against dark backgrounds appear brighter than when viewed against bright backgrounds.
– Power density – More powerful LEDs packed into a smaller physical size can appear subjectively brighter.
– Individual variability – People’s eyes respond differently; some retinas are more sensitive to certain colors.
For most general lighting purposes, perception tests have found that white LEDs provide the most visually comfortable brightness, as they produce a full spectrum of light.
But for applications like traffic signals, the high luminous intensity makes green LEDs appear very bright, despite our eyes being less sensitive to the longer wavelengths. Red LEDs are commonly used for tail lights for similar reasons.
Measuring LED Brightness
To get objective measurements of LED brightness, specialized instruments are used:
Spectroradiometers – Measure the luminous intensity spectrum of light sources. This data can be used to calculate total luminous flux and efficacy.
Goniophotometers – Measure luminous intensity across different angles to characterize the radiation pattern of LEDs.
Integrating spheres – Used with spectroradiometers to measure total luminous flux in all directions.
With these instruments, the brightness of LEDs can be quantified in terms of standard photometric units like lumens and candela. This allows comparing LED products from different manufacturers.
Brightness Across LED Lifetime
Another factor to consider is how LED brightness degrades over lifetime. All LEDs gradually lose luminous output over time. This effect is accelerated at higher operating temperatures.
Here are typical lumen maintenance figures for different LED colors:
|Lumen Maintenance at 50,000 hours
This shows white, blue and green LEDs degrade more over their lifetime compared to red and orange. However, the difference is not so substantial if operating conditions are optimal. Most quality LED products will maintain 70%+ of initial brightness after 50,000 hours.
When it comes to the brightest LED color, there are a few factors to consider:
– Luminous efficacy – Green LEDs produce the most lumens per watt.
– Luminous intensity – Green LEDs also have the highest light intensity output.
– Perception -Green and yellow LEDs appear brightest to human vision.
– Lifetime – Some colors like blue degrade faster over time.
While measurements like luminous efficacy and intensity show green to be objectively brightest, for most applications white LEDs provide the best overall results due to good color rendering and visual comfort.
Nonetheless, choosing the LED color with the right brightness characteristics can make a big difference in lighting performance. Applications like traffic signals and automotive lighting are optimized by using intensely bright green and red LEDs.
With their long lifetimes and energy efficiency, LEDs have revolutionized many lighting applications. Advancements in materials and manufacturing continue to improve their performance and brightness.
In summary, while green LEDs produce the most lumens and have the highest luminous intensity, white LEDs tend to appear subjectively brightest and provide the best color quality for most general lighting applications. But factors like surrounding conditions, power density, and individual eye response also influence perceived brightness. Objective lab testing is required to quantify and compare the brightness of different LED colors accurately.