LED Growlite as an enlarger light source?

<p>There are quite a number of sites and postings on the web which describe using LEDs for building an enlarger light source for LF work. These generally involve mounting individual LED's or short LED strips in an array on a panel (often with a heat sink provision) and also require the fabrication of a purpose-built electrical power supply. Not an impossible task, but a something of an underaking and a bit expensive to purchase all of the individual components.<br>

Lately, LED panels intended for use as "Growlites" for growing plants indoors have become widely available (just check eBay). These have a large number of LEDs mounted on a (usually) 12 inch square panel and operate directly with 110V. Some are available in different colors, including white. Similar offerings are backlit light boxes intended for display of transparencies. Both of these are offered for less cost than the individual components needed for a DIY project, and would avoid most of the fabrication work.<br>

It would seem to be a simple matter to add a diffusion panel in front of the LEDs to build a low cost diffusion light source.<br>

My question is has anyone in this forum done this and what has been your experience? I have read that using VC filtration with white LEDs is limited to contrast grades below 3.5 to 4.</p>

<p>TIA</p>

<p>I used the tri-colour PCB from an LED stage light to make mine. It works very well. It's o.k. from grade 1 to about 3.5 although I have heard that higher grades are possible with the inclusion of some UV LEDs.</p>

<p>Just as long as it's <em>very</em> diffuse output - I tried making a lightbox of my own, using half a dozen LEDs and some crinkled silver foil but it wasn't anywhere near uniform enough an output.<br>

For that $cheap, go give it a shot and report back :)</p>

<p>The Growlites appear to have several hundred LEDs per square foot; the liteboxes somewhat less, but significantly more than half a dozen.</p>

<p>I looked into this some time ago, with a view to converting a cold-cathode enlarger. At that time hi-brightness white LEDs were quite expensive, so I put the project on hold and haven't yet got around to completing it.</p>

<p>Anyway, during my initial investigations I did a simple spectroscopy test on a number of white LEDs. Turns out they have quite a nice spectrum. Pretty flat from red through to cyan with no nasty spikes, then there's a bit of a dip in the visible blue and heightened violet/uv emission compared to daylight, but really not a bad match. Much better than any fluorescent tube, for example. In short I don't forsee a problem with using white LEDs for VC printing, but a better solution might be to use a mixture of blue and green LEDs and a dimmer arrangement between the two. That way you could eliminate the need for filters altogether. Or you could augment the white LEDs with some pure blue ones.</p>

<p>Meanwhile I've got 120 each of red, green and blue LEDs waiting for me to assemble them into a full colour head. But time and tide wait for no man!</p>

I'm considering a project like this, with green and blue LEDs (a mix of blue and UV might be a good idea), controlled by a microcontroller. It'd have a front panel where I could directly dial in the grade and set the timer.

 

However, the enlarger bits I have (have the head, without the ligthsource part) is a condenser enlarger, not a diffuse one. What are the requirements for a condenser light source? Can it be a point light source or does it need to be diffused too, and does it need to be at a specific distance from the condenser lenses? I'm having a surprisingly hard time finding this info online.

<p>I cannot say if a led has a continuous sopectrum<br>

remeber the problems trying to take photographs under florescend<br>

lighting? Lat time I priced white LEDS they were $5,00 each.<br>

A suggestion would be a screw-in 21 led 12v bulb<br>

about $5.00 on the auction site<br>

second, wait until the day after Christmas and buy a disounted<br>

string of white LED Christmas tree lights.</p>

<p>oops I meant a screw in 120v bulb<br>

there are auto replacement LED bulbs but they may only be red.<br>

many enlargers use a smaller bayonet based bulb<br>

we areare thet an auto bulb may have offeat pins and 2 contacts on the bottom<br>

so it would not make an enlarger bulb.</p>

<p>Janne. Whether you need a point source or a diffuse bulb will depend on the enlarger. Most condenser type enlargers are only suitable for use with an opal bulb, because the condensers aren't of high enough quality or of the correct focal length. Also standard LEDs have a built-in lens which limits the emission angle and gives a semi-collimated beam. This beam is extremely difficult to re-diffuse unless a heavy diffuser panel is used with a resulting substantial loss of light.</p>

<p>I've found that a better solution is to grind or file the lens end off the LEDs, leaving a flat and roughened end.</p>

<p>You might be better off looking at tri-colour halogen display lights. I noticed these in a shopping centre recently. They're basically a small halogen reflector with 3 separate filaments and a tricolour filter arrangement over the front. They're used for continuously changing colour displays in shop windows and the like. I haven't managed to track down a supplier or find out the cost yet, but I know they exist because I've seen them!</p>

<p>Why is it when I come over to photo.net,someone always wants to reinvent something? No offense intended to you people,but do you know how to do a google search? www.de-vere.com/news-led.htm after you read the news release,check under products. Your problem is solved.</p>

<p>That DeVere light source looks good but some of us would rather build our own. Especially if we can't really afford a factory built version.<br>

Also some of us just like making things and wouldn't consider buying something which we can make ourselves.</p>

<p>"Why is it when I come over to photo.net,someone always wants to reinvent something? No offense intended to you people,but do you know how to do a <a href="../large-format-photography-forum/00Ximo" target="_blank">google</a> search? www.de-vere.com/news-led.htm after you read the news release,check under products. Your problem is solved."</p>

<p>It is a given that it is possible to built an LED enlarger light source. The point of posting the question was to ask if it were possible to do so using readily available components and thus avoid expense and fabrication effort.</p>

"Why is it when I come over to photo.net,someone always wants to reinvent something?"

 

Because reinventing stuff and building your own things is fun? And fun is why we're here after all, right? I mean, if all I wanted was decent pictures of scenery I would do much better by selling my camera gear and buy postcards instead.

<p>Plus, not everyone owns a Devere enlarger.</p>

<p>Rodeo Joe-the led light source from Devere is availble for other makes of enlargers, not just Devere. Go take a look at the product description again,and you will see the list covers most of the usual brands. So you don't have to have a Devere.</p>

<p>I just finished changing over my Beseler 4x5 to LED. Wanting to keep it very simple, I took out the condensor, added a medium weight plastic diffuser panel, and bought this PAR38 bulb: PAR38-12X2WF-XPW-001W from <a href="http://www.ledtronics.com/Products/ProductsDetails.aspx?WP=C857K775#774">http://www.ledtronics.com/Products/ProductsDetails.aspx?WP=C857K775#774</a>. I used a cheap E26 base extender to bring the blub closer to the diffuser panel. I then lined the inside of the housing (was black) with pure white mat leftover from framing projects. I had to cut a slot in the mat to allow the insertion/removal of the contrast filter drawer. The result was less than 0.1 stop variation edge to center across the diffuser and slightly higher overall light output than the original condensor with a 150W bulb. Instant on/off, no heat generation, constant light output, and 50,000 hour rating on the bulb. </p>