Philips had the best reflector design but weak LEDs. I considered gutting and replacing with CREE XML with an external battery pack mod. This has been done and well described on another forum.
Do you mean the efficiency?
I mean they're an older generation to regarding efficiency, there's definitely that, but my eyes really like the color distribution in the light they put out. It's the best I've used on a bike light while riding. I'd rate them Philips Saferide (vs) > BT20 > Most other blueish/purplish leds.
That's interesting to hear someone did replace them, maybe I'll search for it...I know there's a lot of factors though. The kind of light the LED puts out (replace the LED get different light output), the LED needing to be the same die size, and figuring out an external power source on top of that. Unfortunately can't just plug in an external pack via the usb port (light turns off if you do).
Fenix BT20 is a single LED design with a longer throw than the BT30 dual LED light. I also prefer the switch ergs on the BT20 because the button is ever so slightly larger and being recessed, it is easier to turn on or increase power when wearing winter gloves or lobster mitts. The only place to effectively mount the BT30 is on the handlebar due to its weight (batteries are contained in the unit) IMHO whereas the BT20 has a separate battery unit so, the headlamp is relatively light and can easily be supported by a NOB on the fork or even a NOB on clip on Tri bars. YMMV
I've had a bit of a problem getting the BTR20 to not jump up on down when I hit bumps. The "attach with a band" system hasn't been 100% stable for me... :-/
I definitely agree the BT20 goes further down the road than the BT30. I think some of that might be the BT30 having a brighter nearfield light and eyes adjusting to the brighter part. The BT20 is nicer than the Saferide in having more "to the side" light - the Saferide has a strict cutoff at the horizon, and I have to admit it's nice to have a little more light above that cutoff. As well as for turning, the Saferide wasn't bad but the BT20 is better. But the Saferide's smooth and even beam down the road is nicer for seeing down the road imo - the bt20's flashlight spot is a little annoying being brighter on the road inside the spot and dimmer outside the spot. I think the Saferide goes further if absolute maximum throw down the road is the most important thing.
The bt20 on high is definitely brighter than the saferide as well, though not by as much as you'd expect from the lumen difference. Probably because of how well the saferide's light output is designed and shaped.