Replacing enlarger lamp with LED lamp - color temperature n brightness matter?

[perfectedmaya]

hi

with help from wootsk, i bought a LED lamp (brand is Megaman), from its specs in
http://www.megaman.cc/products/led/l...D/?voltage=12v
it states:

Lumen Output: 240lm
Max. Lumen Intensity: 1,300 cd (which i take it to be 1300 candela)
Colour Temperature: Warmwhite (2800K) (it means 2800k color temperature )


My original lamp in the Durst 1200 enlarger uses General Electric ELC 250W 24V lamp, I found out that its spec is:

brightness is 800 lumens
color temperature: 3400 Kelvin



My question is does the color temperture matters? What difference will I notice and what should I take note of?

As for the change in luminosity, I guess it could only mean longer development time if my new lamp is not as bright. It should not have any other issues right?

tks alot

[ic-racer]

hi

with help from wootsk, i bought a LED lamp (brand is Megaman), from its specs in
http://www.megaman.cc/products/led/l...D/?voltage=12v
it states:

Lumen Output: 240lm
Max. Lumen Intensity: 1,300 cd (which i take it to be 1300 candela)
Colour Temperature: Warmwhite (2800K) (it means 2800k color temperature )


My original lamp in the Durst 1200 enlarger uses General Electric ELC 250W 24V lamp, I found out that its spec is:

brightness is 800 lumens
color temperature: 3400 Kelvin



My question is does the color temperture matters? What difference will I notice and what should I take note of?

As for the change in luminosity, I guess it could only mean longer development time if my new lamp is not as bright. It should not have any other issues right?

tks alot

Since you already purchased it , why don't you try it out and let us know how it works. Since that lamp is a replacement for a 35W lamp, and the original is 250W I suspect it will be much dimmer. Howerver, it it only consumes 6W of energy, so heat should not be a problem for the very long exposures.

[vinny]

it's a 12v lamp, not 24v as your original. It'll likely have a color cast (green), it won't be nearly as bright, illumination may not be as even depending on how your mixing chamber handles it. other than that it sounds perfect.

[DKirk]

Only one way to find out, but it does look like LED technology has evolved significantly to do this - once I've re-joined the ranks of the employed I'll be having a go at a conversion of a Strand Patt 23 to one of the high power LEDs that kick out 3400 plus lumens (it'll do for still lifes, but I rekon it'll be within the next 5 years before it'll be cost efective for me to source ones powerful enough for less than patient sitters on LF). Have a look at some of those on ebay from the boys in China - think the seller is called LED DNA or something close to that.

[Mark Woods]

The color temperature is going to change the contrast since it's going to be adding more of the red spectrum. Whatever notes you have are going to be useless due to the lower output (about 1/4) and the color shift. It may or may not be green, but it could just as easily have more UV or IR. Give it a try and let us know how it works.

[Scott Davis]

It's my understanding (but I could be completely wrong on this) that LEDs are richer in UV than tungsten bulbs. They also fall somewhere between fluorescent and incandescent in terms of spectral continuity - they don't have the green spike that fluorescents do, but they do have a sharper cut-off in the parts of the spectrum they are weak in than incandescents do. I could be completely wrong about this, so if anyone has better information, I'd love to hear it. I do know that LEDs are normally cooler in color temp than incandescents (they come in pretty close to 5500K, if not cooler). I've been using some in my house and the ones on the rheostat circuit sometimes flicker. This could be a real problem if you're using them in an enlarger.

[Sevo]

It's my understanding (but I could be completely wrong on this) that LEDs are richer in UV than tungsten bulbs.

So far, it is quite an effort to get any UV from LEDs - the ones that do will only emit relatively small amounts of very near UV-A, and nobody uses these expensive low intensity LEDs to generate white light. Cheap "white" LEDs are intense blue combined with a yellow fluorescent, the better ones have complex fluorescent pigments, just like modern (compact) fluorescent tubes. How good their colour is will depend on type and grade - like CFL tubes they are made in any common colour temperature, and in CRI grades from abysmal (20) to excellent (90).

[Leigh]

Note that Color Temperature knows absolutely nothing about the green component of white light.
CT is only a measurement of the ratio of red to blue.

If you compare two lamps with identical CT ratings, one could be distinctly green and the other distinctly magenta.

This is due to the fact that when the Color Temperature measurement was defined, the only light sources available were thermal emitters, all of which follow the same spectral curve, so if you knew the ratio of red to blue you knew exactly what the green level was.

- Leigh

[perfectedmaya]

Hi all

tks so much for the answers.. The post on color temp. is really educational, i was searching high and low for the effect 2800k (my LED) has on multi grade paper. If i tune my all color head filters to zero, will I still get grade 2 paper as compared to the original 3400k Halogen lamp. It seems that the answer is no and it has got nothing to do with the change in color temperature, but rather the kind of light it emits.

I have bought a new transformer, so that is why I can use the new 12v lamp.

Yes, i will give it a try this weekend or next. But I always prefer to be more prepared.

I will focus on B/W printing for the time being.

[Mark Woods]

Leigh is absolutely spot on. And again, the added red spectrum will affect you contrast settings. Just look at your contrast filters. They're kinda red, at least mine are.