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/led-reflector/ER1006-35H24D/?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/led-reflector/ER1006-35H24D/?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.

[Sevo]

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.

Subtractively so. They are magenta, that is, they filter green and pass blue - multigrade papers are blue and green sensitive, shifting the balance between these colours will adjust contrast. The issue with "white" LEDs is that they are a blue emitter with what is mostly a yellow phosphor - even when the eye perceives them as "too green", they really are "too blue and yellow", and have not enough light in the green spectrum, yellow already being "safe light" for multigrade. LED Multigrade heads tend to be made up of monochromatic blue and green LEDs, with white ones, if any, only thrown in for focusing.

[ic-racer]

You don't have to be concerned with color spectra theory. Test your new lamp and dichroic head at max magenta and then at max yellow with a step wedge. If the results are acceptable, then proceed to make good photographic prints!

[Rafal Lukawiecki]

I wonder if anyone is still working on a controllable, multigrade, LED light source, preferably with a nice timer. I would be interested in buying one for my 504.

[Leigh]

they really are "too blue and yellow"
Sorry, no. You're combining apples and oranges in an attempt to create an onion.

Blue is one of the three primary colors: red, green, and blue.
Yellow is one of the subtractive primaries: cyan, magenta, and yellow.

Yellow when converted to its primary components is red + green.

So saying that something is "blue plus yellow" means it's blue plus red plus green, which is the definition of the primary spectrum.

- Leigh

[Leigh]

yellow already being "safe light" for multigrade.
Yellow is safe for multigrade papers only when the emitter is a sodium-vapor lamp,
which emits monochromatic yellow light, not a combination of red and green.

- Leigh

[Sevo]

Sorry, no. You're combining apples and oranges in an attempt to create an onion.

Blue is one of the three primary colors: red, green, and blue.
Yellow is one of the subtractive primaries: cyan, magenta, and yellow.



Only if we are talking about three-colour print systems which the human eye cannot distinguish from the real spectral colours. Each of the above colours except for magenta is a (optionally single-wavelength) spectral colour - that we can substitute intermediate colours with a blend (and can perceive a artificial range of red/blue blended non-spectral "purple colours") is purely a artefact of our visual system.



So saying that something is "blue plus yellow" means it's blue plus red plus green, which is the definition of the primary spectrum.


No, it does not, at any rate not if we are talking about actual physical colour. http://en.wikipedia.org/wiki/Spectral_colour

LEDs themselves are highly monochromatic (i.e. they emit a single spectral wavelength, with only a bit of banding due to impurities). To increase output, bright, cheap "white" LEDs will use a single yellow (not red plus green) phosphor on top of a blue LED. If you can't believe it, simply check the output from a cheap white LED with a prism - they have a blue and a yellow to orange band, with no relevant red or green.

[Harold_4074]

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

Some folks use "transformer" (an alternating-current device) when they really mean "power supply" (which can deliver direct current). All incandescent lamps will work on either direct or alternating current, but LEDs, unless they have an integrated power supply, are inherently direct-current devices. Since I'm at work, I couldn't access the .cc domain to see what the lamp in question uses, but I suspect that it will turn out to be a direct-current device.

[Drew Wiley]

This is getting sorta like, if you don't know what's wrong with your car engine, just try putting in one part or another until it works right. Too bad that some of these newer light
sources don't always have published real spectrograms. And yes, the specific spectrual output and not merely perceived color counts, beacaue printing materials see differently
than our own eyes. There are also potential diffusion issues related to how particular mirror
boxes or condensers, etc operate. Tricky at times when you're attempting to switch from
a long-term standardized lamp and something basically adolescent, which might or might
not be around next time. And contrary to someone's previous post, the kind of tungsten
bulb used in modern enlargers is halogen and relatively high in UV. You have to go a ways
back to the old opal lamp days if your think it's more like an ordinary lightbulb.