Light output of 240 W Enlarger bulbs
 

I have finally got around to trying an LED bulb in my enlarger - Durst M800 - attracted by the lower voltage and cooler running temperature.

I had been using a Phillips Tungsten 150w E27 Screw fitting mains bulb and above the bulb Ilford multigrade filters.
Because of mains voltage variation I run this from a large 12v leisure battery and inverter about which I have posted on previously:

http://www.film-and-darkroom-user.or...=Mains+voltage
http://www.film-and-darkroom-user.or...=Mains+voltage

Based on the recommendations on FADU threads particularly by Richard Gould, I tried a Paul Russels warm white (nominally 2700ºK) 15W LED bought through t'internet (B&Q was a waste of space in this respect) . This worked fine. The box said this LED bulb is equivalent to a tungsten 125W bulb.
I was interested in exploring the availability of higher wattage LED bulbs to reduce the times of exposure when printing my maximum 12×16" Prints. The highest wattage suitable LED bulb (again 2700ºK) I could find on t'internet was 18W Bell bulb which they say on the box was equivalent to 100W Tungsten.
To compare the light output of the bulbs in the enlarger I used my RH Zonemaster Enlarging Exposure Meter set to read in its densitometer mode. Once I had got my head round the way it zeros (and rezeros) and records relative densities on a logarithmic (base 10) scale, I compared a number of bulbs in my possession:

The relative light output results as ‘f’ stop steps relative to the brightest:

BULB ‘f’ Stop Steps
150w Tungsten 0
18w LED -1/3
15w LED -1/2
75w Tungsten -11/3
6w LED -11/2

NB the layout of the results is OK if I edit it but reverts when I save it...apologies if it has become confusing.

I would be interested in hearing of any higher wattage LED bulbs and source.

Mike

If I wrap the text in #CODE# tags I get the following - is that the correct formatting Mike?

Yes, indeed it is....mystery solved although in the 'Word' document in which I first drafted the post I managed to make it even clearer IMO by making the fractions of the ' 'f' Stop Steps ' a superscript but that may be a step too far (file attached).

Thanks, Mike

Not exactly a higher wattage bulb but a friend of mine “modified” a De Vere 203 condenser enlarger by removing the existing lamp house, replacing it with a lump of kitchen counter top to which he stuck, by means of lots of mastic and gaffer tape, a 30W LED security lamp facing down. Bit of a Heath Robinson affair but it worked for him. The layers of work top were adjusted to give the right distance for the condensers.

Due to health reasons he has since dismantled his darkroom and disposed of his equipment so I cannot photograph it for you.

Bill

I had problems attaching the file and exceeded my edit time limit. Here is another go.

Interesting, but I think I will tolerate the increased exposure times and think about this type of workaround should it becomes a problem or I am feeling particularly adventurous.

Thanks, Mike

Just out of curiosity, how does all of this workout in terms of lumens?
As I understand, watts have more to do with energy consumption rather than brightness.

Mike, how do you manage the spectral output of each of the LEDS, so they match the Y/M/C output of a bulb - or am I over thinking it ?

Martin

Yes, that is why LED and other more efficient lamps have an "equivalent to N watts tungsten lamp" rating on the box. But even these should be taken with a pinch of salt as lumens refers to the total light output but some LED lamps (in the interest of saving the cost of more LEDs) direct their light across 180 degrees rather than in almost all directions like a normal tungsten lamp does so a given lumen output in this case would mean a brighter area under the LED lamp. For this reason, there is the concept of a "useful lumen" which is a measure of the lumens emitted over a 90 degree cone - but I have not seen this used anywhere in practice... Reflector lamps should give a very similar intensity of light per lumen as they have a directed beam.

Efficiency is often quoted in lumens per watt, which really shows how bad tungsten lamps are. A rough estimate is to multiply the LED wattage by 6 to get the tungsten wattage for a normal bulb lamp and 10 for a directional lamp - but those are only a rough guide as efficiency of the power supply, how hard the LEDs are being driven and the beam directionality vary a lot.

Basically, the only real way to tell is do what Mike has already done! :D

I think the best way to tell check out the brightness of your LED bulb is to make comparison prints.
I had a 75 watt tungsten pearl bulb in my Leitz Valoy 11 enlarger, and bought an 11watt LED bulb (2800K) to replace it. This was supposed to be the equivalent of 75watts tungsten. But it turned out to be brighter. With the tungsten bulb in place I made a print with a known negative. 26 seconds produced a nice print. When I switched to the LED bulb, and kept filters and Fstop the same, 20 seconds exposure produced an identical print.

Alan