CHAPTER 10 ■ LEDSLux or footcandle (fc) measurements describe how much light falls in a given area at a given distance
away. It doesn’t tell you how much total light is coming out of an LED from all sides, nor does it say how
evenly distributed the light is.
Super Ultra High Brightness to the Max
LEDs are often advertised in categories such as high brightness, super brightness, and ultra brightness.
These terms are purely subjective and there isn’t any industry standard. Sorry, but they’re meaningless.
LED Efficiency
Efficiency is how much electricity goes in compared to how much light comes out. LEDs are becoming more
and more efficient with advances in technology. This is particularly important to battery-powered robots.
For visible light, efficiency is measured in lumens per watt (lm/W). Recall that lumens measures total
light output, regardless of direction. Take your total light (lumens) and divide that by your total power (watts)
and that tells you how much power was used for each drop of light.
Unfortunately, few manufacturers specify lm/W. This makes it very difficult to tell if a “high-efficiency”
LED really is more efficient. However, in most cases, true “high-efficiency” LEDs do illuminate better at
lower power levels.
Extreme Close Up of an LED
Most LEDs have two wires, called leads (see Figure 10-8). You must connect positive voltage to the anode
lead and negative voltage to the cathode lead. An ordinary LED won’t light if the leads are connected in
reverse. Not only that, but the diode-characteristic of an LED prevents electricity from even passing through
it in reverse.
Figure 10-8. Anatomy of an LED