Lumens: confusing or misleading?

[schroeds]

Hmmm. so I recently purchased a Dosun front light from Plant X online where it's described as "590 lumens max brightness" (as it is on several other sites as well)
http://www.planetx.co.uk/i/q/LIDOSF375F ... ront-light

However the product packaging describes it as "375 +/- 10 lumens" and the model number is... SF 375 (clue there?). The packaging doesn't mention 590 lumens at all.

Looking into it I came across the same product described in multiple websites as 590 lumens, and others that list it as "590 lumen (measured 375 lumen)"
http://www.onyerbike.co.uk/bike_accesso ... _light_usb

What's going on here?

[biker jk]

There's often a significant gap between claimed lumens and actual/measured lumens. Most of the cheap Chinese lights make outrageous claims on lumens, while the more expensive name brands also occasionally overstate brightness but by nowhere near the same magnitude.

[AUbicycles]

Aficionados prefer LUX as a measurement of light rather than Lumens. Lux measure light 'received' on a surface and is based on a rigid guide which means that there is better accuracy and reliability.

Lumens, as biker jk suggests, can be highly variable.

Beyond the light power, a good optic is important for quality light as hotspots on super-bright lights can be less effective than a more balanced light with lower output.

Christopher

[jules21]

ohh, I studied this in engineering!

Lux measure light 'received' on a surface and is based on a rigid guide which means that there is better accuracy and reliability.

yes, illuminance (lux) is the amount of light received on a surface. if you're interested in lighting up the footpath ahead of you, this is the relevant measure of how brightly a light does that and how clearly you can see the surface.

Lumens is a measure of the amount of light coming from the source - i.e. the light itself. it's the measure of brightness that others see when looking at the light.

both measure are useful for different purposes. it's harder to use illuminance as a benchmark as focusing a light so that emits across a narrower (solid) angle will yield a higher illuminance (light up a surface more), but over a smaller area. Lumens arguably provides a balanced measure of the light's true capacity.

I'm unsure why the light has different lumens ratings - but it may just be different settings - lower lumens setting will yield less brightness (lumens and lux) but longer battery life.

[MattyK]

590 lumens would be a theoretical value, based on:
maximum rated brightness of the emitter, under perfect conditions with full current applied
emitter performs at the top of its "bin" (the brightness category the manufacturers put them in)

Or just an outright lie.

In reality, the actual brightness gets reduced by electronic inefficiency, bin tolerance, the LED heating itself up, and optical inefficiency. 375 sounds realistic in that regard.

Is it a problem? Probably not. Your eyes respond to light intensity in a logarithmic fashion. Plus there are many more factors in lighting to worry about. Warm/cool colour, colour rendering, even light distribution, etc.

Still, send them some feedback that you're disappointed with the lies they sold you.

[bychosis]

Unfortunately it is a number that gets the punters, bigger must be better! Sounds like you were misled in your purchase though, if not in the actual product.

[find_bruce]

Two lights identical except #1 has a narrow spot beam & #2 has a wide flood beam. Both will produce the same lumens but #1 will have a higher lux reading & will appear brighter.

Both lux & lumens tell you something useful about the light.

The biggest difference is that you can measure lux with a cheap meter. To measure lumens however you need a light integrating sphere. Last time I looked the cheapest was over $10k.

So part of the reason people exaggerate or lie about lumens is because it is hard to check if it's true.

[Trevtassie]

Worthwhile checking any light to see if it's sold in Germany, it'll have a realistic rating and useful beam in that case, as their rules are strict.

[schroeds]

Brilliant (no pun intended!) answers as always. Thanks guys

Sometimes trying to get manufacturers provide accurate information to consumers really feels like an uphill battle

cheers