Low-e-coating
Previous  Top 

Low-e-coating: Color variation with angle of incidence

Configuration file
../demo/code/low-e/low_e_demo_angle_variation.wcd

Main window

low_e_demo1

What do you see?
Here you can see a simple low-e-coating example. Low-e stands for low emission - the task of the coating is to decrease heat losses by the strong infrared emission of window glass in buildings. The emission is reduced by increasing the reflectance of the pane by a silver layer. Transmission in the visible is achieved by packing the silver layer in between two oxide layers of appropriate refractive index and thickness. The layer structure of the coating is sketched in the upper right part of the window. The reflectance spectrum is drawn blue, the transmittance green. The colors of the R and T spectra are visualized to the right.
One problem (or a feature) of low-e coatings is the variation of their color with viewing angle (or angle of incidence of light). This variation is investigated in the following actions making use of manual slider settings and the parameter animation and parameter variation features of CODE.

What can you do?
·Move the angle of incidence slider with the mouse and observe the change in the spectra and the colors.  
·Click on the A symbol in the upper left corner. This starts a parameter animation: The angle of incidence is slowly scanning the interval 0 ... 80 deg while all spectra and colors are instantly updated. Pressing the A symbol again stops (or re-starts) the animation.  
·Now click on the Next view symbol in the upper right corner of the screen. The CODE configuration contains two views, and the symbol click loads the second view which looks like this:  

low_e_demo2

·In this view you can vary the layer thicknesses of the coating and study the corresponding changes in the spectra (now displayed in the upper right corner). Try a little bit to get a feeling for the effects of thickness changes.  
·Clicking the V symbol starts a parameter variation action: The angle of incidence is varied from 0 to 80 deg in 5 deg steps. The computed spectra and the color coordinates for each angle are written automatically to the workbook. The color values are displayed in the view: a* and b* vs. angle in the bottom, a* vs. b* in the upper left part of the screen. Change the thickness values and press the V symbol in order to see the new color variation.  
·Try to find a 'neutral' appearance, i.e. small a* and b* values for each angle. The yellow color box indicates the wanted target range. Concerning the goal to obtain a neutral coating the solution below is almost perfect (the transmission is not very high, on the other hand):  

low_e_demo3