I need a front bike light for pretty quick night riding on roads beside the town. I found one that has 120lm, 30lux, and 92m shining distance.
Is it enough? What parameters should a good front light have?
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A front light needs to have both enough lumens (brightness) and have those lumens pointed in the right places - dictated by the reflector and lens. It also needs a battery (presuming its not dynamo powered) to last the length of the ride with some reserves. Addition things to consider are ease of install and removal from bike and mounting location, and battery size ( do you need to charge after every ride, or once a week?) .
More Brightness is easy to cheap to achieve and easy to sell (Mines bigger than yours), and very easy ti lie about "6000lumen". Reflector and lens is design is hard to achieve and hard to sell "Its not the size, its what you do with it that counts"
There are plenty of cheap Chinese lights on ebay that will do a good enough job for under $50, closer to $20 - they work on the "Bigger is better". For a better light in every way, you need to move away from these to a brand name light costing much more to something that has some brains behind the design.
My budget dictates cheap Chinese lights and accepting the poor light distribution My $25 lights claim 1200 lumen, probably have 600 and its all pointing to a high intensity spot with very little out to the sides.The battery is claimed at 4400mAH, I have measured it at 2000mAH, but do get the claimed 2 hours on high.
As already suggested, refer to the BikeLightDatabase,
Given you can get some decent lights up to 300 lm for under $50 then step it up.
For the most part you get what you pay for in a light.
When you're comparing lights it makes more sense to look at the lux rating. Lux is the measure of "light density" – how brightly an known area is lit up by the light. Lumens measure the light output. You can think of lux as measuring how effectively the lumens are focused on the road. On thing to keep in mind is that a given output in lumens will produce a greater lux reading if the light is a tightly focused beam and a lower rating if the light covers a larger area. So it helps to have a way to compare beam patterns as well as light output.
The lights that I'm most familiar with are German dynamo lights. The Busch & Müller Cyo light puts out 80 lux in relatively wide pattern. It is a very nice light to ride with on dark roads – it feels like a car with good headlights. The beam is well controlled, cars don't seem to mind it, and I get lots of positive "that's a really bright light" comments. The light (without a dynamo hub) costs about $100. If you ride much at night it is totally worth it – I run mine all the time, in the daytime it helps to make the bike stand out when you're riding in the shadows on bright days.