Help Candela and light measurement

[Jupitus]

One for the physicists perhaps, or maybe photographers etc...

Candela - Wikipedia, the free encyclopedia

There is the definition of Candela, as the name suggests a measurement of light intensity.

For an LED brakelight, the legal guidelines are:

in the case of a stop lamp fitted to a motor vehicle not being a motor bicycle, first used on or after 1st April 1991 either centrally or in such a manner as to project light through the rear window the intensity of the light emitted to the rear of the vehicle shall be not less than 20 candelas and not more than 60 candelas when measured from directly behind the centre of the lamp in a direction parallel to the longitudinal axis of the vehicle.

My question is how to I 'add up' LEDs? If I have 10 LEDs which are all 1 candela each, is it as simple as saying that makes 10 candelas total ???

Thanks :wub:

 

[Chilly]

Interesting question. In terms of total light emitted it will be equivalent, but not from a point source which is what the limitation is about. there is probably an equation with area in it somewhere.

I'd go by limit > (Cled * n) / 4 at a guess.

 

[Draylor]

Yes, it seems to be.

But arent you taking this a bit far here? Noones actually going to scientifically measure the brightness of your brake lights, whether its on a car, bike, or whatever. As long as they can be seen clearly at a reasonable difference but at the same time wont blind anyone that gets too close its fine. Isnt it?

 

[Jupitus]

Yes, it seems to be.

But arent you taking this a bit far here? Noones actually going to scientifically measure the brightness of your brake lights, whether its on a car, bike, or whatever. As long as they can be seen clearly at a reasonable difference but at the same time wont blind anyone that gets too close its fine. Isnt it?

Well... if it were only for my car I wouldn't worry, but I may offer them for sale at some point, so it makes sense to at least TRY to make sure I know the legal situation

 

[Chilly]

The point of the limit, Draylor, is that someone else has already thought of all of that and given a suitable limit. Jup - if you are going to sell them I'd definately get an authoritative answer.

 

[Draylor]

And the point of not caring is that an actual brightness test isnt part of any MOT as far as I can tell.

 

[Tom]

LEDs are more directional than filament bulbs, you must consider this if you're changing your brake lamps to use LED bulbs. Cars with LED brakes from the factory are designed to be seen from a wide range of angles, aftermarket lights may not be.