I did a comparison test between the MAGLITE 2-D Cell LED Flashlight and the 3-D cell version (ST3D016), and found them to be almost identical in terms of beam shapes and brightness. Note that both flashlights I tested have the same second-generation LED technology (Luxeon Rebel ES 3W LED) in them. First-generation Maglite LED flashlights (sold before 2009) have the older Lux III LED in them, which is about half as bright.
Now, onward with the comparison:
From the outside, both 2-D and 3-D Maglite LED flashlights have exactly the same shape and finish. Naturally the 2-D cell version is shorter, but the difference is not as dramatic as one may expect. That's because the 2-D version actually has the length of four D cells stack together. So the 3-D version is only 25% longer.
There is a subtle difference in the positive contact inside the two Maglite flashlights. The ST2D has a slightly recessed contact point, which means if the first battery's positive terminal is just slightly wider than that of a standard alkaline cell, it will not make electrical contact. So initially I was not able to use any rechargeable D cells (such as the Energizer D Rechargeable NiMH) in it. I have to add a tiny solder bump to the positive terminal for it to work.
On paper, the ST2D should produce more light output than ST3D (114 lumens vs. 104). But in real life, I cannot tell which flashlight is brighter even in a side-by-side comparison. They both have the same LED and the same optical reflector design, which means they should generate the same brightness as long as they are driven at the same power.
According to my own measurements, both versions consume roughly the same input power (hence light output) with fresh alkaline cells. The main difference is in how the input power changes over battery voltage range.
- For the ST3D, input power is tightly regulated at 1.9-2W as long as the battery voltage is over 3.5V. Below 3.5V, however, the power drops rapidly. The light becomes nearly useless when battery voltage drops below 3V.
- For the ST2D, input power is not as well-regulated. It consumes about 1.7W at 3.0V (two fresh alkaline cells). As the battery falls all the way down to 1.5V, the input power actually increases to almost 2.2W. Below 1.5V, the input power drops off quickly, but the light is still useable even at 1.0V!
(See the "Input Power vs. Battery Voltage" chart in Customer Images section)
A typical alkaline D-cell is rated for about 9,000mAh when delivering a constant current of 500mA. So its total energy (assuming an average voltage of 1.3V) is about 12Wh. Based on my energy calculations:
- Two alkaline D cells should be able to power the ST2D for about 12 hours at full brightness.
- Three alkaline D cells should be able to power the ST3D for about 20 hours at full brightness.
There is absolutely no way three alkaline D cells can sustain 2W for 72 hours, because that will require each cell to pack 48Wh of energy. Why did MagLite rate the runtime for ST3D as '72 hours'? I can only imagine that's the time it takes for the light to drop to 10% of its full brightness.
The 2-D and 3-D versions of MagLite LED flashlights are identical in terms of built-quality, light output, and beam shapes. The main difference is their runtimes. But this difference is more like 12 hours (for 2-D) verses 20 hours (for 3-D), instead of 9 verses 72 as Maglite claimed. Presently, the two versions are priced similarly. So unless you expect to use your Maglite as an impact weapon, the shorter 2-D version may be a better choice.