Visibility of LED (Light Emitting Diode) clock displays and the distances that they can be seen is a very subjective matter. In addition, other factors associated with the specific installation must be considered. In particular the viewer's eyesight, digit size, ambient light and digit color are the most important. We offer this discussion as a guide for helping estimate the LED digit size that may be required for a particular application.
Masterclock offers clock displays with digit sizes ranging from .6" (1.5cm) to 8" (20cm) in size.
All clocks use diffused LED digits, which appear as (7 segment) lighted bars.
The .6" (1.5cm), 2.3" (5.8cm), 4" (10cm), and 7" (18cm) clocks are available with
red, amber, green, or blue LEDs.
Typically (to most people) the red LED displays are the most visible,
however under lower light conditions the amber and green can be more pleasing
and less distracting to the eye.
A guide, when deciding which size clock is best, is 1" of LED for every 50 feet
of viewing distance. Therefore, a .6" (1.5cm) display could be considered
for distance up 30' (9m), a 2.3" (5.8cm) display for distances of 100' (30m), etc.
Consider however, that at these distances, a person would have to stop and concentrate
to see the displays. If the user needs to know the time by simply glancing at the clock,
the distance to size ratio should be cut (at least) in half.
Therefore, if a person were to glance at a clock from 50' (15m) away,
he would need a 2.3" (5.8cm) display, at 100' (30m) he would need a 4" (10cm) display and so forth.
These distance estimates will be severely compromised by ambient light conditions
and digit color. If the application is critical we suggest that you experiment with printed
digits, or better, a sample display, and verify which size is adequate for your application.
| Digit Size | Maximum Viewing Distance | Typical Viewing Distance |
| .6" (1.5cm) | 30' (9m) | 15' (5m) |
| 1.8" (4.6cm) | 90' (27m) | 45' (13m) |
| 2.3" (5.8cm) | 100' (30m) | 50' (15m) |
| 4" (10cm) | 200' (60m) | 100' (30m) |
| 7" (18cm) | 350' (100m) | 175' (50m) |
