Lights: lumens versus watts

rflynnr

I've been running Cateye NC250 twin lights on my commuter during the winter for about six or seven years. It has served me well during that time but I've noticed a significant drop-off in the ability of the battery to retain a charge and I'm considering moving to another system. (I have priced a new battery but even if I can convince Cateye to send it to me from the US, it'll cost €114 before p&p.)

Trouble is, the Cateye ran two halogen bulbs - a 12w and 20w - and I'm finding it difficulty to figure out how this compares with modern HIDs or LEDs whose output is measured in Lumens. I know wattage and luminosity are essentially different scales of measurement but is there any rule of thumb I could use to compare lights offered by online stores with my existing setup?

Chips Lovell

The whole watts vs lumens vs candlepower thing had me bamboozled when I was shopping around and I never got to the bottom of it. In the end I relied on user reviews and a few sites that compared output by taking photos.

tunney

Watts isn't a measure of the output of the lights - its a measure of the consumption of power of the lights.

Lumens and lux are the important ones. Lumens being output, lux being lumens per metre squared area.

Gavin

Dinotte claim a 200 lumen light is equivalent to a 15-20w Halogen.
I think a 10-13 watt HID is equivalent to around 500 lumen.

I'm only quoting what I've seen from forums, I don't know the actual lumen per watt output of a Halogen/HID

More detailed info at
http://en.wikipedia.org/wiki/Luminous_efficiency

It's hard to track the comparison versus LEDs as LEDs are developing so quickly

Ghost Rider

I guess that means flynnr's question should be rephrased as "What is the relationship, if any, between the input (i.e. power consumption) of a light and its output?"

tunney wrote: »

Watts isn't a measure of the output of the lights - its a measure of the consumption of power of the lights.

Lumens and lux are the important ones. Lumens being output, lux being lumens per metre squared area.

DirkVoodoo

Watts will be the energy dissipated and is not really related to brightness.

Some energy will be dissipated as light, the rest as heat so it depends on the type of bulb used really. An LED is obviously much more efficient than an incandescent bulb so it is difficult if not impossible to relate the brightness of the two based on wattage.

Stick with what Tonto suggests and go by reviews where they offer photos or some other kind of visual comparison.

rflynnr

Ghost Rider wrote: »

I guess that means flynnr's question should be rephrased as "What is the relationship, if any, between the input (i.e. power consumption) of a light and its output?"

What he said.

Anyway, in the end I googled "expected output in lumens from halogen bulb" and found a site that gave me a rough and ready answer that appears to suggest that a 20w halogen would be expected to produce between 350-400 lumens of light. Not sure what that says about Dinotte's figures though.

Lumen

Don't get too hung up on numbers.

Lots of watts may mean not much brightness if the light isn't efficient.
Lots of lumens may mean poor illumination if the beam pattern is poorly shaped for your needs.
Lots of lux may not be that useful if the lux reading is taken at the centre of a very small hotspot. And with lux readings measuring distance is critical.

For road use, I think the shaped beams produced by the Busch and Muller lights (e.g. the Ixon IQ Speed). Busch and Muller have beamshots and lux@10m info on their website.

Or you can just get a torch (endless threads on this) and live with the round beam pattern but great value for money.