The Optics Debate (and field of view)


Headlights intended for use with dynamo systems are designed to work with the lower intensity 2.4-3.0 watt lamp bulbs. They use a tightly focused beam that illuminates directly in front of the bicycle, but that doesn't provide much illumination to either side.

There is one Usenet poster that claims, endlessly and incorrectly, that the optics of the dynamo headlights are vastly superior to the optics of the MR16 series of lamps commonly used with high powered, battery-operated headlights. The optics of the dynamo headlights are not superior, they are simply different. They have been designed specifically to use the limited intensity of the HS3 bulb to provide a very narrow beam. The narrow beam is a compromise, not an advantage!

Why would anyone want any visibility to the sides, after all you're riding on the road, not off on the sidewalk. The reason is obvious; you want to be able to see other bicycles (unlit), dogs, children, pedestrians, etc. We're not talking about illuminating trees, but illuminating a reasonable angle of your field of view.

Lighting expert Marty Goodman wrote (regarding the Cateye Stadium light): "Equally if not more significantly, the sides of the road were illuminated quite brightly by the CatEye Stadium, where even with all three of my lamps lit, illumination to the sides of the road was minimal. CatEye states that it designed the reflector for the Stadium for a narrow 10 degree beam. But what I experienced in using the Stadium was a bright area in a ten degree beam ahead of the bike, PLUS a 30 degree or more wide area illuminated less brightly, but still far more brightly than with any of my other lamps. QUALITATIVELY far more brightly."

Goodman continues: "With all my other lamps, I feel like I'm riding into a narrow tunnel of safe visibility. With the CatEye Stadium, night riding becomes more like riding during the day, with objects on the side of the road clearly visible both close to the bike and quite a ways ahead."

Note that Goodman's other lamps were already far brighter, and had a wider field of view, than any dynamo lights (he compared the stadium light against a 6 watt/10 watt CatEye dual beam NC200 system AND a NiteRider 15 watt cyclops), neither of which are the best battery-powered lights available.

Goodman concludes: "The extremely wide area of illumination does make for much greater safety, but it also removes that sense of "silently rolling thru a tunnel of light thru the night."

Personally, I'll take the extra safety, at least while commuting.

H.I.D.-Like Brightness and Field of View using MR16 Lamps

You can achieve a similar level of illumination, both in brightness and field of view, with two MR16 lamps (albeit less efficiently in terms of lumens/watt, but for a lot less money). You can use one 20W flood or narrow flood, plus one 20W spot or narrow spot. You could also use a 10W flood or narrow flood, plus a 10W spot or narrow spot, and over-voltage by 20%. Commercial dual-lamp bicycle lighting systems will often have one narrow spot beam (8), and one narrow flood beam (24), often of different wattages--there is no way to do this with dynamo powered lights.

Another dumb claim is that since MR16 lamps were not originally designed for use as bicycle lights, that this somehow makes them inferior to dynamo powered lights. The fact is that there are literally hundreds of different styles of MR16 lamps, tailored for specific applications. They vary by beam angle, reflector type, color temperature, voltage, wattage, lens versus no lens, etc.. They were not designed for automotive driving lights, display case lights, or interior lighting either, but the overwhelming advantage of the precision matched optics and small size made them desirable for many applications outside the original use (overhead projectors and microfiche readers). There are MR16 lamps designed explicitly for bicycle lights. They are lower wattage, and have different beam angles, reflectors (and are more expensive).


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