What is Solar Rejection and Light Transmission?

“Solar Rejection”, or “Total Solar Energy Rejection” as you might hear it called, is more than temperature reduction percentage, although it may translate roughly into temperature reduction, it shouldn’t be confused or compared with it.

Solar rejection is based on a metric that describes the total amount of solar energy (Ultraviolet + visible light + Infrared) that is blocked, or rejected as it were, from passing through a window. This metric is called “Total Solar Energy Rejection”, often referred to as “TSER”.

Before making any assumptions about heat rejection, you should be looking at Total Solar Energy (UV + visible + IR) first, because the Infrared rejection number only helps people to understand that the film on the window is rejecting much of the heat from infrared rays. It does not mean that if a significant portion of the IR is blocked then no heat will be transmitted through a film.

Films with a higher TSER do not always make a better performing window film, as a film with a high TSER could also be darker, or highly reflective. The best way to assess the type of window film you need is to compare films with the same visible light transmission, or “VLT”.

Visible light is the reason we can see. Light moves as a wave, effectively bouncing off of objects and our eyes so that we can see them. Without this light, we’d be in total darkness. In physics, light can refer to any kind of electromagnetic wave. This, of course, includes radio waves, infrared, ultraviolet, and visible light, among others.

When you direct light towards an object, the light bounces off of its surface to create a reflection. Specular reflection happens when the light reflects off of a shiny surface – like a mirror. Diffuse reflection is when the light illuminates a dull object.

Light can also move through material objects, and depending on how it does this, we could call it light transmission, refraction, or absorption.

Transmission of light is when those light waves move through the entirety of a material object, without being absorbed. A material might have a different transmittance for visible light over infrared light, and these are what effects how much light can be transmitted through an object.

An example here would be this: If you shone a light through an object, let’s say a window. The first thing that happens, is a small percentage of that light reflects off the outside of the window. Next, the light continues through the window, but a larger percentage of it is absorbed by the molecules of the window, itself. Finally, the percentage of light left is what emerges of the other side. It’s the final percentage that tells you how much transmittance that window has. That is light transmission.

“Ultrasky” are a range of lantern skylights, engineered by Ultraframe. This company also manufacture a comprehensive range of glazed roofing solutions, and are the market leaders in conservatory and glazed roofing, with over 30 years’ innovative experience.