Difference Between Red and Blue Light

Key Difference – Red vs Blue Light

The key difference between Red and Blue light is the impression created at the human retina. It is the perceptive understanding of the difference between two wavelengths.

Characteristics of Red Light and Blue Light

Some creatures cannot see different colours except black and white. But, humans identify different colors in the visible range. The human retina has approximately 6 million cone cells and 120 million rod cells. Cones are the agents responsible for sensing colour. There are different photoreceptors in a human eye to identify basic colours. As shown in the following figure, there are specially designed, separated cones in human retina to identify the difference between Red and Blue light. Let us go through the facts behind Red and Blue in detail.red light vs blue light

By using V=fλ, the relationship between the velocity, wavelength and frequency, the characteristics of Red and Blue light can be compared. Both have the same velocity as 299 792 458 ms-1 in a vacuum, and they lie on the visible range of the electromagnetic spectrum. But when going through different mediums, they tend to travel at different velocities which make them change their wavelengths while keeping the frequency a constant.

Red and Blue can be treated as components of the sunlight. When the sunlight goes through a glass prism or diffraction grating kept in the air, it resolves basically into seven colors; Blue and Red are two of them.Difference between Red and Blue light

What is the difference between Red and Blue Light?

Wavelength in a vacuum

Red Light: Approximately 700 nm corresponds to light in the Red range

Blue Light: Approximately 450 nm corresponds to light in the Blue range.


The Red light shows more diffraction than Blue light since it has a higher wavelength.

It should be noted that the wavelength of a wave is subjected to vary with the medium.


We see colours, thanks to the cone cells in our retina which respond to different wavelengths.

Red Light: Red cones are sensitive to longer wavelengths.

Blue Light: Blue cones are sensitive to shorter wavelengths.

Energy of a Photon

The energy of a certain electromagnetic wave is expressed by plank formula, E=hf. According to the quantum theory, energy is quantized, and one cannot transfer fractions of quanta, except an integer multiple of quantum. Blue and Red lights consist of respective energy quanta. Therefore, we can model,

Red light as a stream of 1.8 eV photons.

Blue light as a stream of 2.76 eV quanta (photons).


Red Light: Red has the longest wavelength in the visible range. Compared with Blue, Red light shows less dispersion in the air. Therefore, Red is more efficient when used in extreme conditions as a warning light. Red light undergoes the lowest deviated path in mist, smog or rain so is often used as park/ Brake lamps and in places where hazardous activities are in progress. On the other hand, Blue light is very poor in such situations.

Blue Light: Blue light is hardly used as an indicator. Blue lasers are devised as revolutionary high-tech applications such as BLURAY players. Since the BLURAY technology needs a precisely fine beam to read/ write extremely compact data, Blue laser came to the arena as the solution, beating Red lasers. Blue LED is the youngest member of the LED family. Scientists had been waiting a long time for the invention of the Blue LED to make Energy saving LED lamps. With the invention of the Blue LED, energy saving concept has streamlined and increased in many industries.

 Image Courtesy:
“1416 Color Sensitivity” by OpenStax College – Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013. (CC BY 3.0) via Commons 
“Dispersion prism”. (CC SA 1.0) via Commons