Lumens & Kelvin ????

[colinicky]

Ok I think that Kelvin means the temperature of the light ? ie the higher the Kelvin the more white the light is Am I correct ?
So what does Lumen mean ?
Can you have to much of each ? or is higher always better ?

[Reikimaster]

Kelvin is the colour tempertature.
Something up at the 5500-6000 is a nice white light of a HID rather than the orange glow of a Halogen (not sure where LED's usually fall)

Lumens is the brightness
but not sure of the scale


[edit] just re read that, not much help am i??

[thehuntsman81]

Colour Temperature by definition it is the temperature required for a pure black body to emit a specific colour... think of piece of steel being heated by an oxy torch, as the temperature rises the steel changes colour. Daylight is around 5700K. Cooler than this you get reds and hotter than this you get blues. As Reikimaster says you should be aiming for 5500 to 6000K to get a nice white light, close to daylight.

Lumens is a measure of perceived light power in that it is the total amount of light power visible to the naked eye.

Total bulb power tells you very little as 90% of that power may be used to emit a light that our eye cannot see leaving us only 10% of usable light power. Therefore Lumens is used to give us a useful idea of of how much usable power we are actually seeing from our bulb. The reflector of the bulb also plays a part but you get the point.

The higher the lumens the brighter the bulb

[jhewitt]

Discussed this with one of my torch suppliers/manufacturers who was a bit cagey cos I reckon it doesnt mean a lot. If the reflector tightens the beam to cover only half as much area then it gives twice as many lumens but this doesnt make it a brighter light just a light that covers half the area. My interpretation may be wrong but if so please put me right. Meanwhile have a look at my torches on Torches

[NeilB]

Quite a nice, easy to understand explanation is here Lux - Wikipedia, the free encyclopedia

LED and HID are all up in the 5500 to 6000K these days but HIDs produce a lot of infared and ultraviolet light .... so wasted energy compared to a LED that only produces visible light.

[dry suit diver]

Originally Posted by jhewitt

Discussed this with one of my torch suppliers/manufacturers who was a bit cagey cos I reckon it doesnt mean a lot. If the reflector tightens the beam to cover only half as much area then it gives twice as many lumens but this doesnt make it a brighter light just a light that covers half the area. My interpretation may be wrong but if so please put me right. Meanwhile have a look at my torches on Torches

no thats why the best measure is the efficacy of a lamp. how many lumens output per watt

[thehuntsman81]

Originally Posted by jhewitt

Discussed this with one of my torch suppliers/manufacturers who was a bit cagey cos I reckon it doesnt mean a lot. If the reflector tightens the beam to cover only half as much area then it gives twice as many lumens but this doesnt make it a brighter light just a light that covers half the area. My interpretation may be wrong but if so please put me right. Meanwhile have a look at my torches on Torches

lol this is turning into a photometry lesson!!!!

Essentially this statement is wrong but no worries. The lumen value is a value related to the bulb and not the reflector used. The lumen value is the total amount of light power coming from a point source which in this case is the filament. It can be measured quite accurately using an integrated sphere.

Your advisor is mistaken with "candlepower". Candlepower is a measure of the maximum intensity of light at any given point in the light beam. A more tightly focused beam will have a higher intensity of light.

Essentially a lumen is a measure of luminous flux and a candlela is a measure of luminous intensity. For a specific bulb the lumen value never changes but the candela value changes depending on how this light is focused in the reflector.

Therefore you should be looking for a torch with a bulb that has the highest possible lumen value as that is the most powerful regardless of the reflector.

You then look at the candle power value to see how tightly the beam of light from the reflector will be. If two lights had similar lumen values and one had a higher candlepower value, what it would mean is that light had a more tightly focused beam.

In my opinion don't get bogged down in physics cos its pretty boring and figures are often fudged to make a product sound good. Go and test the light you are thinking of buying and make a judgement based on what you see not what is written on the box!!