Xenon lamp supply chain issues.

[Leo Enticknap]

These guys make LED illumination units to retrofit into Victorian magic lanterns, for those who don't fancy blowing themselves up with real limelight.

One of those units would likely work in a typical 16mm classroom projector - their light output is similar - if it weren't for the fact that they are too big - the heatsink is around a 4x4x4 cube.

A LED or laser illumination source in a film projector would have the same big advantage that their use brings to telecine/datacine technology: the ability to adjust the color temperature of the light source to correct dye fading on a film print. But as Harold points, although LEDs waste a smaller proportion of their power input as heat than xenon, they still waste a significant amount. Still, the lamphouse cooling CFMs needed would be lower, as would the electricity cost per lumen.

[Marcel Birgelen]

Interesting. I just looked up a comparison between LEDs and lasers. The optical bandwidth of an LED is about 25 to 100 nm, while that of a laser is less than 5 or 10 nm. So, LED could be used for reduced speckle. However, the electricity to light efficiency of the LED is about 10 to 20% while the laser can be up to 70%. A xenon lamp is apparently about 4 to 14% efficient. The peak output of a xenon lamp is at about 825 nm while the visible spectrum is about 380 to 700 nm. So, the xenon lamp has a lot of output, we just can't see it. It appears that LEDs would be better than xenon as far as efficiency and better than laser as far as speckle, but nothing beats the efficiency of the laser. There MIGHT also be the possibility of LEDs being available at wavelengths corresponding to the peaks of the XYZ curves, while lasers tend to be on the skirts increasing metamerism.

Can you elaborate on those numbers for LED? Because the conversion of electric power into photonic power of most modern LEDs is far more efficient than 10 to 20%, actually if done right, it far exceeds 80% efficiency. I guess those efficiencies are based on the total effective efficiency from source to screen for current LED technology used for projection?

Up until now, I've only seen LEDs being used for small scale projectors, it looks like LED doesn't scale as efficient as laser does.

[Harold Hallikainen]

The various efficiencies were from a quick web search yesterday. I should have cited the source. https://www.dial.de/en/blog/article/...f-a-white-led/ puts LEDs at about 45%.

[Carsten Kurz]

I guess it also plays a role how the emitted light can be used to a higher extent in the light engine. Classic 'bulbs' are very bad at this. Lasers offer smaller etendue per design and offer far more flexibility and higher 'overall' efficiency. This also impacts visual contrast improvements.
I assume LEDs are somewhere inbetween. Don't know about the conversion efficiency for phosphor lasers, but I assume, once light passes through the phosphor wheel, there goes the small etendue.

[Jim Cassedy]

TaDah! A wholeboxa 4K bulbs I was waiting for finally arrived today.
NuBulbs.jpg
I wonder if it would have been any faster if instead of four 4K's,
I had asked for one 16k?

[Tom Bert]

I guess it also plays a role how the emitted light can be used to a higher extent in the light engine. Classic 'bulbs' are very bad at this. Lasers offer smaller etendue per design and offer far more flexibility and higher 'overall' efficiency. This also impacts visual contrast improvements.
I assume LEDs are somewhere inbetween. Don't know about the conversion efficiency for phosphor lasers, but I assume, once light passes through the phosphor wheel, there goes the small etendue.

That is correct: "luminous efficiency" is only part of the equation; how to (efficiently) get to the kilolumens needed for cinema is the other part. Because of etendue 1+1<2 when it's about lumens. The bigger the etendue of each individual building block, the more losses when combining. If (random numbers, don't quote me on it) 1+1=1.5 for lamps and 1+1=1.99 for lasers (minimal etendue) then 1+1=1.6 for LED