Let's talk about PWM. In fact PWM isn't good even if you can't see or hear it (click on the picture to see the details).
Most of us own "1000 LM" EDC (Every Day Carry) flashlights which most of time are operated at about 25% or 250LM, right? 250LM is just enough for most tasks and provide alot of runtime. Let's do some math using CREE's datasheet data.
The flashlight market is populated mostly by FET PWM electronics. If you own a PWM light (high or standard freq., no matter in this case) it always runs at full output in all modes. In 250LM mode instead of constant lighting it generates short pulses. CREE XP-L V6 at 3 Amp 60°C produces 1152 lumens (constant current mode) which is translated into 288 lumen average with 25% PMW fill. But, if you're driving the same LED with a constant 750mA current (which is 25% of 3 Amp), the same LED produces 381 lumens! It's nearly 100 lumen above the 288 lumens provided with the PWM. This remarkable difference is provided by the fact that LED efficiency is getting much better at a lower current. Short high-current pulses waste a significant part of electrical power on useless heating.
Now if we don't need these extra lumens, if we want to stay with the "standard" 288 lumen output, how much power it will take in "no PWM" mode? You'd hardly expect that the CREE XP-L requires just 556 mA of constant current to produce the same luminous flux as a PWM torch running at 750mA. In runtime figures it's 6 hours 6 minutes with a "standard" 18650 3400mah battery versus 4 hours 30 minutes in PWM mode.
Many guys still feed his torches by CR123A primaries. This difference is directly converted into 25% cash savings on lithium batteries.
By the way, the new LUX-RC 371D light engine which we've made for FL33 torch, runs three XP-L V6 in series. It needs just 5.6W of battery power to produce 1000 lumens. The torch stays just a little warm and runs 2 hours and 15 minutes with the most common 18650 3400mah battery. The extra hour is provided not only by the "No PWM". The light engine driver uses lossless switching power conversion (boost driver), which features almost zero heating loss.