[Laser] LED versus Lumens questions

[Vlacilik, Radovan]

Hallo optical group,

I would like to ask you about the LED and lumens.

1.)

Lumen is unit of Luminous flux (optical power) and it reflect the varying sensitivity of the human eye to different wavelengths of light. Sensitivity of the human eye has peak at green and the eye sensitivity for the red light is aprox. 10 times lower.

But If I look to the Luxeon 3 LEDs:

Colour Part Min Lumens Typ Lumens Wavelength Type Rad. Pattern 

Green LXHL-LM3C 51.7 @ 700mA 80 @ 1A 530 nm Star Hex Lambertian 

Red LXHL-LD3C 90 @ 1.4A 140 @ 1.4A 627 nm Star Hex Lambertian 

I do not undestand why the Red one has bigger Lumens that Green one. I can see that red one has bigger current, but by my opinion if the rule above is correct the green LED should has bigger value of lumes than red one.

 

2.)

The nex thing I would like to ask you is Lumen per Watt.

Lumens per watt is a measure of efficiency in converting electrical energy to light. Multiply this by the watts dissipated in the LED to get lumens. 

When you look to the LR W5SN Osram LED datasheet:

http://www.farnell.com/datasheets/85000.pdf <http://www.farnell.com/datasheets/85000.pdf> 

You find the values:

Typical Luminous flux for the red one = 70lm

Optical efficiency for the red one = 60lm / W

Power consumption is 3.4W

So the Luminous flux should be 3.4W * 60lm/W = 204lm!

Or backwards

Power consumption should be 70lm / 60lm/W = 1.17W!

 

I am sorry - the questions are elementary, but I need to clear them up. 

Many thanks for the answers.

Have a nice weekend.

Rado om2zz

http://radosan.ic.cz/ <http://radosan.ic.cz/>