Luxeon Lens

[Ubergeek63]

Other studies have found blue light to be dangerous.
**broken link removed**The ideal wavelength for scotopic vision is 498nm which is cyan. You can get 505nm cyan LEDs which is near enough the ideal wavelength.

True, but if you do the math you end up with more lumens from blue LEDs than from cyan.[/QUOTE]The information from that link is interesting in that it supports both positions.

I can understand causing retinal damage at the intensities they are doing the tests at. However, it also states that the iris is opened by a preponderance of blue light in the spectrum. That means that more light gets in allowing you to see at lower light levels, which reduces the power consumption and by extension the chances for retinal damage.

Dan

 

[Hero999]

True, but if you do the math you end up with more lumens from blue LEDs than from cyan.

The information from that link is interesting in that it supports both positions.[/quote]
Do you, the eye is more sensitive to cyan than blue and according to the datasheet the cyan is brighter.

 

[Ubergeek63]

Do you, the eye is more sensitive to cyan than blue and according to the datasheet the cyan is brighter.

Luminous Efficacy

Cyan photopic =303Lm/W scotopic=1700Lm/W
Blue photopic =62Lm/W scotopic=1149Lm/W

Typical LED (rebel blue 23, cyan 70 both at 700mA) cyan 130Lm, blue 48Lm

Scotopic Lm:
Cyan: 1700/303*130=729Lm
Blue: 1149/62*48=890Lm

So, because the ratio of scotopic to photopic is so much greater even though the photopic output of the blue LED is roughly 30% of that of the cyan, it is still brighter to scotopic vision!

 

[Hero999]

That doesn't look right to me.

The lumen figures on the datasheet are already weighted to account for the varying sensitivity of the eye at different wavelengths. You need to get the power output in radiant power output then weight it to account for scotopic vision. The problem is that most LED manufactures don't list the radiant power of their LEDs and they don't say whether the figures they give are rated for the photopic or scotopic vision.

 

[Spadez]

This topic has gone offtopic slightly :s

I want to know what kind of lens I can construct using sheet aluminuim inside the body of the light to give even distribution of light on the top surface, something like the lens of a maglight.

I was thinking a bit of polished aluminum above the luxeon, which deflects the beam downwards, then plates at the bottom which bounce it back up.

 

[Ubergeek63]

That doesn't look right to me.

The lumen figures on the datasheet are already weighted to account for the varying sensitivity of the eye at different wavelengths. You need to get the power output in radiant power output then weight it to account for scotopic vision. The problem is that most LED manufactures don't list the radiant power of their LEDs and they don't say whether the figures they give are rated for the photopic or scotopic vision.

Actually they are always photopic. Lumens are by definition photopic. Declaring a "scotopic lumen" number is more for a frame of reference.

The Lumen was the first and was used as a reference for everything else. In the horticulture industry lamps were sold by their lumen rating, but once people smartened up thel industry started using the "plant lumen" adopting the term that everyone was familiar with with the qualifier that it was scaled for plant growth. Now there are other plant efficacy graphs that, like scotopic and photopic, distinguish between different varieties and life cycles in the of plants.

Dan

 

[audioguru]

You cannot put a solid piece of metal in front of the LED. Then no light will be directly above it.
Maybe hundreds of slits and each slit gets wider as its distance is farther from the center? A nightmare to make in a hex shape.

 

[Ubergeek63]

This topic has gone offtopic slightly :s

I want to know what kind of lens I can construct using sheet aluminuim inside the body of the light to give even distribution of light on the top surface, something like the lens of a maglight.

I was thinking a bit of polished aluminum above the luxeon, which deflects the beam downwards, then plates at the bottom which bounce it back up.

Well if you do not mind the lower efficiencies of the previous generartions of Luxeons, get batwings. Normal reflectors and such will not do it for you.

For the newer ones you need to get the custom optics. The best thing is to get the one that suits your needs. If, for instance, you have sufficient LEDs for your dining room table but table is rectangular you will have 30-50% more light on the table if you use 30/60 optics. The combination of the proper spacing, beam angle, and height above the work surface can make for a nice even lighting.

Some fancy expensive LED fixtures are futuristic looking: foot diameter metal rings that serves both as structure and heat sink, for four lighting class LEDs and lenses that is hung from the ceiling like a chandolier.

Dan