LS/O - Lux at 10m? BETTER QUESTION

Bandgap

Enlightened
Joined
Aug 14, 2002
Messages
284
Location
London
Skip to post below for my second attempt at the question

Does anyone have an intensity figure (in Lux) for a white Luxeon Star/O measured at 10 metres (33 feet)?
 

Doug S

Flashlight Enthusiast
Joined
Jun 20, 2002
Messages
2,712
Location
Chickamauga Georgia
Originally posted by Bandgap:
Does anyone have an intensity figure (in Lux) for a white Luxeon Star/O measured at 10 metres (33 feet)?
<font size="2" face="Verdana, Arial">Lux is a unit of illuminance [lumininous flux density] not intensity. *If* you use the intensity value from the Luxeon datasheet of 180 cd, this would yield an illumination of 1.8 lux at 10 meters.

Edited: Changed from 0.18 to 1.8 lux. Thanks to Jon for sharp eye.
 

Jonathan

Enlightened
Joined
Dec 14, 2001
Messages
565
Location
Portland, OR
Originally posted by Doug S:
Lux is a unit of illuminance [lumininous flux density] not intensity. *If* you use the intensity value from the Luxeon datasheet of 180 cd, this would yield an illumination of 0.18 lux at 10 meters.
<font size="2" face="Verdana, Arial">Lux is lumen per square meter, right? Cd is lumen per steradian? So at 1 meter, the illuminance measured in lux should be numerically equal to the intensity in Cd, and at 10m the illuminance measured in lux should be 1/10^2 the intensity in Cd, or 1.8 lux. Am I missing something here?

-Jon
 

Doug S

Flashlight Enthusiast
Joined
Jun 20, 2002
Messages
2,712
Location
Chickamauga Georgia
Originally posted by Jonathan:
</font><blockquote><font size="1" face="Verdana, Arial">quote:</font><hr /><font size="2" face="Verdana, Arial">Originally posted by Doug S:
Lux is a unit of illuminance [lumininous flux density] not intensity. *If* you use the intensity value from the Luxeon datasheet of 180 cd, this would yield an illumination of 0.18 lux at 10 meters.
<font size="2" face="Verdana, Arial">Lux is lumen per square meter, right? Cd is lumen per steradian? So at 1 meter, the illuminance measured in lux should be numerically equal to the intensity in Cd, and at 10m the illuminance measured in lux should be 1/10^2 the intensity in Cd, or 1.8 lux. Am I missing something here?

-Jon
</font><hr /></blockquote><font size="2" face="Verdana, Arial">Jon, you are right on all counts. I misplaced the decimal.
 

Bandgap

Enlightened
Joined
Aug 14, 2002
Messages
284
Location
London
Thanks for the explication, I need some more help.

I shall work through your information tonight to ensure I understand it all.

In the meantime....

.... What I was actually asked to do, by the UK's Cyclist Touring Club, was to compare possible future Luxeon-based bike lights with existing bike lights.

I was provided with this information:

"Peak illumination from a halogen dynamo lamp (2.4W) is typically quoted at 10 to 15 lux.
That is conventionally measured at 10m distance, so it translates to 1000 to 1500 candela."

Can anyone give me a quick answer on if these units are reasonable, and how a LS/O would fare in comparison?

Thanks for your time.

I apologise for my ignorance of matters luminous, for I am an ex-electronic engineer and specialise in Watts, Ohms and nanoseconds.
 

lambda

Flashlight Enthusiast
Joined
Jan 6, 2002
Messages
1,795
Location
Iowa
The basic problem is they are basing their comparisons on peak illumination levels. A Luxeon can be focused into a beam that is 1700 lux, but would not make a very good bike light due to the resulting small bright spot. The beam angle (how tightly foucused) can increase the lux level so that a light which produces less light can be brighter than another more powerful light.

Supplying a better description of what you currently are using would help. Is the bike light 2D cells? Is it as bright as a 2D MagLite? What is the beam spread (10ft circle of light at 8, 10, 12 feet)?

There are some members who have made Luxeon bike lights here. Perhaps just a straight request like "does anybody have a Luxeon bike light?". They may be able to tell you it's as bright as bike light xyz.

Hope it helps........
 

Bandgap

Enlightened
Joined
Aug 14, 2002
Messages
284
Location
London
Thanks Lambda

The idea is to say how many Luxeon Star/Os driven at 350mA it would take to give the same cenral brightness as a conventional dynamo-driven bike light which, after further investigation, produced 17 lux at 10m.

I have had to delay working through the maths, but am trying to find time this weekend.

Steve
 
Top