Exposing Chlorophyll Prints with Artificial Grow Light

with Cristina Zaletta

Chlorophyll printing is one of the most unusual image-making processes in alternative photography because the image is not coated onto a surface — it is formed within one.

In a chlorophyll print, a photographic positive is placed in direct contact with a fresh leaf and exposed to light over time. As light slowly breaks down chlorophyll and related pigments, the exposed areas fade or shift, while the protected areas retain more of their original density. The resulting image appears as a subtle tonal imprint held inside the leaf itself: part photograph, part biological trace.

Chlorophyll printing is deeply tied to the physiology of the plant material: the age of the leaf, its moisture content, its thickness, pigment density, internal structure, and the environmental conditions in which the exposure takes place. That is precisely why artificial UV light has often been considered a poor substitute for sunlight.

Chlorophyll prints exposed using sunlight by our in-person workshop participants June-September 2025

Why UV light alone is usually less effective

At first glance, chlorophyll printing seems like it should work well under UV lamps. After all, many alternative photographic processes depend heavily on ultraviolet radiation. Many of us already work with iron and silver based process, most of us have access to a UV exposure unit and so it makes sense to attempt chlorophyll using that light source.

But chlorophyll printing behaves differently.

Most traditional UV units are designed to deliver a narrow band of radiation, usually concentrated in the UV-A range. That can be useful for iron-salt or dichromate-based processes, where the chemistry is specifically activated by ultraviolet wavelengths. Chlorophyll printing, however, is not driven by a single clean photochemical trigger in the same way.

Instead, it seems to rely on a broader ecological condition: prolonged exposure to light across a wider spectrum, combined with gentle heat, pressure, and time. In other words, what the leaf is responding to is not just “UV” in isolation, but something closer to an environmental simulation of sunlight.

A useful way to think about it is this:

• UV-only light can stimulate damage

• but sunlight creates a fuller degradation environment

  
  

That fuller environment includes:

• visible wavelengths, especially across the photosynthetically active range

• warmth

• and a more natural balance of energy that affects the leaf as a living tissue rather than as an inert photosensitive coating
  

This also aligns with the experience of Cristina Zaletta, who found that full-spectrum LED grow lights were significantly more effective than UV lamps. In their testing, UV lamps did not meaningfully degrade chlorophyll in the way needed for printing, whereas a 60W full-spectrum grow panel covering roughly 400–700 nm proved much more successful. They also noted that heat still plays an important role, and that the leaf performs best when positioned within the lamp’s warmer zone rather than simply blasted with light from a distance.  So the issue is not necessarily that artificial light cannot work. It’s that UV alone often reproduces only one fragment of what sunlight is doing.

Conceptually, does something shift?

I've been on reflecting on the idea that while artificial exposure could work beautifully, it undeniably changes the process.

One of the reasons chlorophyll printing is so compelling is that it places image-making in direct relation to season, weather, duration, fragility, and the living world. The print is not just produced with a leaf — it is produced through the leaf’s own temporality. We are submitting image-making to a biological timescale.

To expose chlorophyll prints under the sun is to accept a certain surrender:

• to daylight

• to slowness

• to climate

• to unpredictability

• to the fact that the process is partly outside your control

Bringing exposure indoors shifts the work away from a collaboration with seasonal conditions and toward a more constructed, controllable photographic setup. That's not necessarily wrong, but the image becomes less dependent on the weather, less tied to a particular time of year, and less entangled with the rhythms of nature. Artificial exposure changes where the conceptual charge sits.

Instead of being rooted primarily in weather, season, and environmental surrender, it can become rooted in:

• translation

• adaptation

• access

• constructed ecologies

• the desire to remain in relation with plant material even when natural conditions are unavailable
  

Artificial exposure introduces a productive tension into chlorophyll printing: the work still depends on a living material, but the conditions surrounding that material become increasingly engineered.

Did you experiment with different light sources before discovering that a 60W full-spectrum LED grow light panel worked well for you? And by any chance, would you have a photo of your setup that you’d be happy to share?

My approach to artificial light sources began in 2023, when I was taking my first steps in chlorophyll printing. Here in Canada, since the start of the autumn, the lack of sunlight becomes quite noticeable. I needed to find an alternative.

In my case, it was more a process of elimination than extensive testing of different light sources. UV lamps—even LED ones—emit energy outside the visible light spectrum (blue range). They stimulate plants to produce oils or resins but do not degrade chlorophyll. Most importantly, they can be harmful to skin and eyes (burns, premature aging, and retinal damage), and they cannot be used for long periods.

Sodium lamps concentrate on yellow and red tones, which brings them somewhat closer to sunlight. However, without blue light, leaves become overly stressed. They also produce a lot of radiant heat and consume a high amount of electricity, so they weren’t a good option for me. Full-spectrum grow lights are the most balanced. They cover the 400–700 nm range, which is where most photosynthesis occurs. This allows them to mimic the sun in the chlorophyll degradation process and produce the print.

They also have several advantages:

• Low energy consumption and long lifespan

• High energy efficiency

• Minimal heat generation

• Optimized light spectrum

• Fully recyclable at the end of their life cycle

That said, some precautions are necessary: wearing protective glasses, never looking directly at the LED diodes when the light is on, and limiting night time use, as they can disrupt our circadian rhythm.

How close do you usually place the light to the leaf? Do you think using two or three 60W full-spectrum LED grow lights could significantly shorten exposure times? Heat seems to play an important role in chlorophyll printing, as it can significantly speed up the

process.

To achieve printing with grow lights, you first need a panel that covers the entire leaf. I’ve been experimenting with multiple separate lights, but I haven’t achieved consistent results yet. Each panel creates a specific heat zone, and the leaf should be placed within that area. This varies depending on the brand, but generally it’s around 6 to 8 cm. To find this zone, you can simply use your hand—moving it away from the lamp, you’ll feel the heat decrease.

I usually limit daily exposure to about 6 hours. The glass temperature, just like with natural sunlight exposure, shouldn’t exceed 40–50°C—you should be able to touch the glass without burning your hand. If needed, I continue the exposure the following day. It’s a process very similar to working with natural sunlight.

Have you found that certain plant species respond particularly well to LED light, perhaps even differently than they do under sunlight? HIs there any clear differences in results when using grow lights compared to sunlight? (tonal range, sharpness, contrast, or color)

There are several leaves that respond well, although since I grow plants organically, I don’t work with a very wide variety of species. I would definitely recommend starting with nasturtium leaves, as they react very well and quickly.The reaction also depends on the leaf’s moisture at the time of printing, but I haven’t noticed anything drastically different compared to sunlight printing.

Most of the leaves I’ve experimented with don’t show significant differences compared to sunlight. Tones and contrast are more related to the age of the leaf on the plant. Younger leaves produce lighter tonal ranges, while more mature leaves create deeper tones. Since I use multiple leaves in my compositions, this actually helps me vary tones and depth in my work. For example, in my project Ancestors of Chlorophyll, where I print 19th-century seed catalogs, I used four different plants with four distinct tonalities:

1. Hollyhock leaves

2. Poinsettia leaves

3. Money Tree leaves (pachira aquatica)

4. Nasturtium leaves

Does the slower or more controlled nature of indoor printing change your relationship with time in the process? Do you approach a print differently knowing it’s being made in an indoor, constructed environment rather than under the sun?

Honestly, I don’t think it’s slower than sunlight exposure—it’s simply more controlled and doesn’t depend on the weather. Not having to consider the climate has definitely changed my approach to the technique. My photographic projects usually involve a research phase before shooting, which takes time, so this method allows for better planning—both in terms of the subject and the plants I want to use.

As for the process, there’s quite a lot of interest. Many people have been asking me about it, so I’m preparing a workshop and an ebook that will be available this autumn with all the details. But honestly, the best thing is just to try it and experiment.