Introduction
This article describes an easy approach to implementing day and night modes of display operation; the example described addresses an approach to swapping between a custom color scheme and the default color scheme applied to the operating system and for that reason it could be applied to a number of different designs. The concept of creating alternative night modes of operations for displays is not new; it has been around in aircraft and automobiles for many years. Night modes of display operation offer a way in which displays may be used in darkness and when interference with the user's night vision is an issue.
Maintaining night vision requires the avoidance of light; any source of light can bleach out vision purple and even a dark accommodated display can cause this reaction quite rapidly. Once destroyed, it takes about thirty minutes for the human eye to become dark adapted again. While it is not possible to make a backlit display such as the LCD displays typically found on laptops and tablets entirely safe for night use, it is possible to reduce the effect of the emission by darkening the display to the maximum extent practical.
Altering the color scheme is beneficial but to make the display safer for night use, it may also be advisable to reduce the brightness of the illumination source. Military displays intended for use in environments where night vision imaging systems (NVIS) are to be used with the equipment will typically offer a mode of operation where the brightness is reduced to eliminate interference with the use of the NVIS device; this is also typical in automobiles where turning on the headlights also reduces the brightness of the illuminated displays in the instrument panel.
The demonstration project only alters the color scheme. When night mode is selected, the field areas of the controls are converted to black and most of the foreground color is converted to green. Without regard to contrast, the human eye is tuned to see the color green better than other colors and specifically green in about the 450 nanometers of wavelength range. It is no accident that early display monitors used phosphors that emit light in this range. As you shift from green to blue-green (e.g., about 480 nanometers of wavelength) the color becomes more saturated and the contrast ratio declines which makes characters rendered in this color less legible on a black background. It is a common misconception that red makes a good color for rendering text on a black background but red is a highly saturated color and it too is difficult to read when displayed on a black background due to the contrast ratio. Naturally white on black or black on white offers the highest contrast ratio but white is a worst case color for this sort of mode of operation and should be used sparingly.
Figure 1. Day Use of Sample Application
Figure 2. Night Use of Sample Application
Getting Started
In order to get started, unzip the included project and open the solution in the Visual Studio 2005 environment. In the solution explorer, you should note the following:
Figure 3. Solution Explorer
As you can see, there is only a single form contained
in this Windows application project (Form1.vb). The only additional reference
added to the project was System.Drawing.Color; all else is per the default
configuration for a form class.
There is not much to the design of the form; it merely contains a set of
controls used to demonstrate the transition from day to night modes of
operation. These controls do not do anything (unless you are interested in
learning the phonetic alphabet):
Figure 4. The Main Form Designer
The Code: Main Form (frmMain.vb)
The main form class includes one import which is necessary to support the sample application:
Imports System.Drawing.Color
The color class import is used to allow the application to manipulate the control colors.
The first block of code in the application is used to terminate the demonstration application whenever the user clicks the form's "Exit" button:
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
Application.Exit()
End Sub
Following the exit button click event handler, the next block of code is used to handle the click event of the Day mode menu option; there are a total of three modes of operation (day, night, and auto):
Private Sub tspDay_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles tspDay.Click
Me.tspAuto.Checked = False
Me.tspNight.Checked = False
Timer1.Enabled = False
Dim obj As Object
For Each obj In Me.Controls
obj.ForeColor = Control.DefaultForeColor
obj.BackColor = Control.DefaultBackColor
If TypeOf obj Is TextBox Then
obj.BackColor = Color.White
End If
If TypeOf obj Is ComboBox Then
obj.BackColor = Color.White
End If
If TypeOf obj Is ListBox Then
obj.BackColor = Color.White
End If
Next
Me.BackColor = Control.DefaultBackColor
Me.ForeColor = Control.DefaultForeColor
End Sub
The code is simple enough, the first part of the block is used to update the check marks in the menu and to disable a timer control used to poll for the time whenever the Auto mode of operation is selected. Next, the control collection is evaluated and the control has its foreground and background color properties set to the default control foreground and background colors. Since the text box, combo box, and list box controls are normally white, the current control is evaluated to see if it falls into one of these three categories and if it does, the background color is set to white. Lastly, the form background and foreground colors are also set to the default options. If you employ other controls on your form with similar requirements, you'd want to perform similar checks on those controls as well.
The next block of code is used to handle the night menu option click event:
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