The Joys of Playing together

**HDTboy** · 1st February 2006, 18:26

We could just decide whether they're foglights, spotlights or headlights, then we'd know where to look in the virm

**Colapop** · 1st February 2006, 18:29

I still got no idea what this thread's about???

**Hitcher** · 1st February 2006, 18:31

Cd = candela, the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

The frequency chosen is that to which the eye is most sensitive. This frequency is normally referred to as the corresponding wavelength: 555 nanometre. The wavelength varies with the medium through which the light passes, so, in the interest of precision, our relatively familiar wavelength description of light is not used in the standard.

The strange choice of the number 683 is to make the value identical to that obtained with the previous version of the unit: the emission from 1 square centimetre of glowing, solidifying platinum.

The steradian is the cone of light spreading out from the source which would illuminate one square metre of the inner surface of a sphere of 1 m radius around the source.

The light intensity coming towards the observer is assumed to be reaching all angles within the enclosing steradian at the same intensity. It doesn't have to in practice: one can perfectly well measure the luminous intensity from a lighthouse beam, knowing that it actually only covers less than a hundredth of a steradian. One measures the light received by a small sensor of known area and multiplies this to give the corresponding value for one steradian.

**Bonez** · 1st February 2006, 18:32

Originally Posted by Colapop

I still got no idea what this thread's about???

Just someone wanting to be in the spotlight as it were.

Move right along folks! Nothing to be seen here.................

**Finn** · 1st February 2006, 18:35

Originally Posted by Hitcher

Cd = candela, the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

The frequency chosen is that to which the eye is most sensitive. This frequency is normally referred to as the corresponding wavelength: 555 nanometre. The wavelength varies with the medium through which the light passes, so, in the interest of precision, our relatively familiar wavelength description of light is not used in the standard.

The strange choice of the number 683 is to make the value identical to that obtained with the previous version of the unit: the emission from 1 square centimetre of glowing, solidifying platinum.

The steradian is the cone of light spreading out from the source which would illuminate one square metre of the inner surface of a sphere of 1 m radius around the source.

The light intensity coming towards the observer is assumed to be reaching all angles within the enclosing steradian at the same intensity. It doesn't have to in practice: one can perfectly well measure the luminous intensity from a lighthouse beam, knowing that it actually only covers less than a hundredth of a steradian. One measures the light received by a small sensor of known area and multiplies this to give the corresponding value for one steradian.

Mate, could you be a little more precise please?

**Colapop** · 1st February 2006, 18:35

Wots a lumen then?

**Hitcher** · 1st February 2006, 18:47

The lumen is the unit of luminous flux. The flux from a light source is equal to the intensity in candela multiplied by the solid angle over which the light is emitted, taking account of the varying intensity in different directions.

**Colapop** · 1st February 2006, 18:50

How then does various opacities affect lumenescience? Such as various films over windscreens or tinted lens covers?

**Hitcher** · 1st February 2006, 19:01

Luminescence is the emission of light by a substance caused by physical or chemical means. Tinted films have no effect on luminescence, merely filtering various parts of the spectrum and so diminishing or filtering the light that passes through.

**Colapop** · 1st February 2006, 19:05

So is/was opacity the right term for this then? Or would it be refraction that applies in the case of tints?

**Hitcher** · 1st February 2006, 19:41

Opacity is a much better term. And if you're talking about tints, then refraction (bending of light) isn't what's happening. They filter light, removing parts of the spectrum, such as certain visible colours or ultraviolet.

**Colapop** · 1st February 2006, 19:43

Opacity affects brightness and refraction affects visual spectrum. Does then radience come under the brightness umbrella? I'll come back for this tomorrow....

**Motu** · 1st February 2006, 20:00

His lights actualy can't be too bright - 100W bulbs are illegal,and even they are not much brighter on the lux meter,practicaly not noticable...although I have never tested HID yet.They can only be out of adjustment,which is why it's pointless him taking a photo - how bright the light appears will depend on where the camera is...duh.The beam tester is the only way to see if they are in adjustment.

**HDTboy** · 1st February 2006, 20:10

HID lights aren't that much brighter on the beam setter, they emit a different colour light though Motu, I'll check one tomorrow for you and let you know the numbers.
The best thing about factory HID lights is that they are self adjusting (have to be under German law) so when you've got 500Kg of cement in the boot of your M3, you still don't blind oncoming drivers at night.