Technical note: Darkroom lighting for luminescence dating laboratory

Frouin, Marine; Grandfield, Taylor; Huebsch, William; Evans, Owen

doi:https://doi.org/10.5194/gchron-2023-1

Preprints

https://doi.org/10.5194/gchron-2023-1

Preprints

16 Jan 2023

| 16 Jan 2023

Status: a revised version of this preprint was accepted for the journal GChron and is expected to appear here in due course.

Technical note: Darkroom lighting for luminescence dating laboratory

Marine Frouin, Taylor Grandfield, William Huebsch, and Owen Evans

Abstract. An optimal lighting setting for the darkroom laboratory is fundamental for the accuracy of luminescence dating results. Here, we present the lighting setting implemented in the new Luminescence Dating Research Laboratory at Stony Brook University, USA. In this study, we performed spectral measurements on different light sources and filters. Then, we measured the optically stimulated luminescence (OSL) signal of quartz and the infrared stimulated luminescence (IRSL) at 50 °C (IR₅₀) as well as post-IR IRSL at 290 °C (pIRIR₂₉₀) signal of potassium (K)-rich feldspar samples exposed to various light sources and durations.

Our ambient lighting is provided by ceiling fixtures, each equipped with a single orange light-emitted diode (LED). In addition, our task-oriented lighting, mounted below each wall-mounted cabinet and inside the fume hoods, is equipped with a dimmable orange LED stripline.

The ambient lighting, delivering 0.4 lux at the sample position, induced a loss of less than 5 % (on average) in the quartz OSL dose after 24 h of exposure, and up to 5 % (on average) in the IR₅₀ dose for the K-rich feldspar samples, with no measurable effect on their pIRIR₂₉₀ dose. The fume hood lighting, delivering 1.1 lux at the sample position, induced a dose loss of less than 5 % in quartz OSL and K-rich feldspar IR₅₀ doses after 24 h of exposure, with no measurable effect on their pIRIR₂₉₀ dose. As light exposure during sample preparation is usually less than 24 h, we conclude that our lighting setting is suitable for luminescence dating darkrooms, it is simple, inexpensive to build, and durable.

Received: 11 Jan 2023 – Discussion started: 16 Jan 2023

Marine Frouin et al.

Status: closed

RC1:
'Comment on gchron-2023-1', Tobias Lauer, 14 Feb 2023

The authors report about the laboratory illuminations in their still relatively new luminescence laboratory and address the important questions about a potential signal-loss among the quartz or feldspar minerals if exposing the material du different, in parts very long durations of laboratory light. They quantify the relation of signal loss and duration of laboratory light exposure at different spots in their laboratory, and conclude that it’s mostly very minor, meaning without a statistically meaningful effect. Consequently, the here tested common ways of subdued light exposure during sample preparation are not of relevance for luminescence dating purposes. Furthermore, they precisely analyze the wavelength range of their laboratory illumination by doing spectral measurements.
The tests they do are of high importance and should motivate other laboratories which have not done such testing yet to follow this approach as it’s urgently necessary to exclude light contamination as a relevant source of luminescence signal loss.
The paper is of high relevance for the international community of trapped charge dating as it yields some very useful new information. The set-up of the experimental design, the overall structure of the paper and language style are of high quality and the contribution is scientifically sound. I personally recommend the paper for publication without improvements necessary.
I have only 1 question for discussion and I would be glad to stimulate a discussion here: Also if the here detected signal loss is not really relevant, still we are talking about a few percent in extreme. Can we do better? Or would the community say it´s not relevant at all?

Citation: https://doi.org/10.5194/gchron-2023-1-RC1
- AC1: 'Reply on RC1', Marine Frouin, 06 Apr 2023
  
  We thank Tobias Lauer for reviewing our manuscript. We agree that any signal loss induced during sample collection and preparation should be a subject of concern, and effort should be made to reduce this effect while maintaining a safe working environment. A robotic system for automating sample preparation would be the ultimate solution.
  Like the reviewer, we are eager to hear more from the community.
  
  Citation: https://doi.org/10.5194/gchron-2023-1-AC1
RC2:
'Comment on gchron-2023-1', Helena Alexanderson, 15 Feb 2023

This is a very nice study of a key aspect of the laboratory part of luminescence dating, the lighting conditions in the lab. Since material that will be dated with luminescence is light-sensitive it is important that lab light does not damage the samples and care needs to be taken to choose lamps with suitable intensity and wavelengths. There are a few but not many previous studies of luminescence lab lighting and this technical note by Frouin et al. is a valuable addition. They document and test the lighting in their luminescence laboratory with different filter combinations and measure the effect on selected quartz and feldspar samples for various time periods. The results show that the preferred light source + filter combination has a very limited effect on the samples and is well suited to luminescence lab work. The experiments are well set up and I particularly appreciate the detailed information on the light sources and that they test effects both on quartz and feldspar. The note and its conclusions would be of high interest to people working in luminescence laboratories.
Specific comments
I would like to have some more information about the samples used in the experiments. If they have been described elsewhere, a reference to that/those publication(s) would be sufficient. For the calibration quartz the paper by Hansen et al. (2015, Radiation Measurements 81) should be mentioned. Otherwise just brief information on natural dose, specification of the feldspar as K-feldspar already in the sample description, in addition to the site and rough age information presently stated.
It would also be interesting with some more discussion about the difference between quartz and feldspar. Currently the larger scatter in the K-feldspar results is attributed to fading, but is the larger decrease in dose with exposure time (compared to quartz) also due mainly or only to fading, or is there some component of higher sensitivity to the light’s wavelengths as well?
Technical corrections
L209 – replace “fold” with “foil”

Citation: https://doi.org/10.5194/gchron-2023-1-RC2
- AC2: 'Reply on RC2', Marine Frouin, 12 Apr 2023
  
  We thank Helena Alexanderson for reviewing our manuscript and for the constructive feedback. Please find our detailed response below:
  1_Sample SB27 was collected from the middle Paleolithic site of Oscurusciuto (Italy). Its quartz fraction had a natural average dose of 133 ± 5 Gy (n=14). The feldspar samples SB 36 and SB 44 were from the last glacial cycle and were collected on Long Island, NY. Sample SB 36 had a saturated pIRIR₂₉₀ signal (2D₀=328±10Gy, n=3). Sample SB44 had an average pIRIR₂₉₀dose of 67±3 (n=12) and a pIRIR₂₂₅ dose of 49±1 (n=11, not fading corrected). The publication of these luminescence results is in preparation.
  2_The results of our experiment on quartz OSL and feldspar IRSL signal depletion after light exposure show the same tendency as the results reported by others (e.g., Bailif and Poolton, 1991; Spooner, 1993, 1994a, b, 2000; Sohbati et al., 2017). K-rich feldspar IRSL signal decay faster than the quartz OSL signal when exposed to yellow-orange light. Sohbati et al. (2017) also showed that Na-rich feldspars bleach faster than K-rich feldspar when exposed to yellow-orange light. The authors argue that the difference in the bleaching response from samples from different origins might be due to variations in the optical transmission of grains due to size, color, and transparency. In the present study, our feldspar samples were collected from glacial deposits and assumed to be K-rich feldspar. Additional analyses on various samples would be required to better understand the relationship between bleaching rate and geochemical composition. In a forthcoming publication, we will report on the bleaching rate for well-characterized samples of quartz and feldspar from different origins under our laboratory lighting conditions.
  
  references:
  Bailiff, I. K., & Poolton, N. R. J. (1991). Studies of charge transfer mechanisms in feldspars. International Journal of Radiation Applications and Instrumentation. Part D. Nuclear Tracks and Radiation Measurements, 18(1-2), 111-118.
  Sohbati, Reza & Murray, Andrew & Lindvold, Lars & Buylaert, Jan-Pieter & Jain, Mayank. (2017). Optimization of laboratory illumination in optical dating. Quaternary Geochonology. 39. 10.1016/j.quageo.2017.02.010.
  Spooner, N.A. (1993). The validity of optical dating based on feldspar. Unpublished DPhil thesis, University of Oxford, UK
  Spooner, N.A. (1994a). On the optical dating signal from quartz. Radiation Measurements, 23, Nos.2/3, 593-600.
  Spooner, N.A. (1994b). The anomalous fading of infrared-stimulated luminescence from feldspars. Radiation Measurements, 23, Nos.2/3, 625-632.
  Spooner, Nigel & Questiaux, Danielle & Aitken, M. (2000). The use of sodium lamps for low-intensity laboratory safelighting for optical dating. 18.
  
  Citation: https://doi.org/10.5194/gchron-2023-1-AC2
AC3: 'Comment on gchron-2023-1', Marine Frouin, 19 Apr 2023

On behalf of all co-authors, I would like to thank the reviewers for their thorough comments.

Citation: https://doi.org/10.5194/gchron-2023-1-AC3

Status: closed

RC1:
'Comment on gchron-2023-1', Tobias Lauer, 14 Feb 2023

The authors report about the laboratory illuminations in their still relatively new luminescence laboratory and address the important questions about a potential signal-loss among the quartz or feldspar minerals if exposing the material du different, in parts very long durations of laboratory light. They quantify the relation of signal loss and duration of laboratory light exposure at different spots in their laboratory, and conclude that it’s mostly very minor, meaning without a statistically meaningful effect. Consequently, the here tested common ways of subdued light exposure during sample preparation are not of relevance for luminescence dating purposes. Furthermore, they precisely analyze the wavelength range of their laboratory illumination by doing spectral measurements.
The tests they do are of high importance and should motivate other laboratories which have not done such testing yet to follow this approach as it’s urgently necessary to exclude light contamination as a relevant source of luminescence signal loss.
The paper is of high relevance for the international community of trapped charge dating as it yields some very useful new information. The set-up of the experimental design, the overall structure of the paper and language style are of high quality and the contribution is scientifically sound. I personally recommend the paper for publication without improvements necessary.
I have only 1 question for discussion and I would be glad to stimulate a discussion here: Also if the here detected signal loss is not really relevant, still we are talking about a few percent in extreme. Can we do better? Or would the community say it´s not relevant at all?

Citation: https://doi.org/10.5194/gchron-2023-1-RC1
- AC1: 'Reply on RC1', Marine Frouin, 06 Apr 2023
  
  We thank Tobias Lauer for reviewing our manuscript. We agree that any signal loss induced during sample collection and preparation should be a subject of concern, and effort should be made to reduce this effect while maintaining a safe working environment. A robotic system for automating sample preparation would be the ultimate solution.
  Like the reviewer, we are eager to hear more from the community.
  
  Citation: https://doi.org/10.5194/gchron-2023-1-AC1
RC2:
'Comment on gchron-2023-1', Helena Alexanderson, 15 Feb 2023

This is a very nice study of a key aspect of the laboratory part of luminescence dating, the lighting conditions in the lab. Since material that will be dated with luminescence is light-sensitive it is important that lab light does not damage the samples and care needs to be taken to choose lamps with suitable intensity and wavelengths. There are a few but not many previous studies of luminescence lab lighting and this technical note by Frouin et al. is a valuable addition. They document and test the lighting in their luminescence laboratory with different filter combinations and measure the effect on selected quartz and feldspar samples for various time periods. The results show that the preferred light source + filter combination has a very limited effect on the samples and is well suited to luminescence lab work. The experiments are well set up and I particularly appreciate the detailed information on the light sources and that they test effects both on quartz and feldspar. The note and its conclusions would be of high interest to people working in luminescence laboratories.
Specific comments
I would like to have some more information about the samples used in the experiments. If they have been described elsewhere, a reference to that/those publication(s) would be sufficient. For the calibration quartz the paper by Hansen et al. (2015, Radiation Measurements 81) should be mentioned. Otherwise just brief information on natural dose, specification of the feldspar as K-feldspar already in the sample description, in addition to the site and rough age information presently stated.
It would also be interesting with some more discussion about the difference between quartz and feldspar. Currently the larger scatter in the K-feldspar results is attributed to fading, but is the larger decrease in dose with exposure time (compared to quartz) also due mainly or only to fading, or is there some component of higher sensitivity to the light’s wavelengths as well?
Technical corrections
L209 – replace “fold” with “foil”

Citation: https://doi.org/10.5194/gchron-2023-1-RC2
- AC2: 'Reply on RC2', Marine Frouin, 12 Apr 2023
  
  We thank Helena Alexanderson for reviewing our manuscript and for the constructive feedback. Please find our detailed response below:
  1_Sample SB27 was collected from the middle Paleolithic site of Oscurusciuto (Italy). Its quartz fraction had a natural average dose of 133 ± 5 Gy (n=14). The feldspar samples SB 36 and SB 44 were from the last glacial cycle and were collected on Long Island, NY. Sample SB 36 had a saturated pIRIR₂₉₀ signal (2D₀=328±10Gy, n=3). Sample SB44 had an average pIRIR₂₉₀dose of 67±3 (n=12) and a pIRIR₂₂₅ dose of 49±1 (n=11, not fading corrected). The publication of these luminescence results is in preparation.
  2_The results of our experiment on quartz OSL and feldspar IRSL signal depletion after light exposure show the same tendency as the results reported by others (e.g., Bailif and Poolton, 1991; Spooner, 1993, 1994a, b, 2000; Sohbati et al., 2017). K-rich feldspar IRSL signal decay faster than the quartz OSL signal when exposed to yellow-orange light. Sohbati et al. (2017) also showed that Na-rich feldspars bleach faster than K-rich feldspar when exposed to yellow-orange light. The authors argue that the difference in the bleaching response from samples from different origins might be due to variations in the optical transmission of grains due to size, color, and transparency. In the present study, our feldspar samples were collected from glacial deposits and assumed to be K-rich feldspar. Additional analyses on various samples would be required to better understand the relationship between bleaching rate and geochemical composition. In a forthcoming publication, we will report on the bleaching rate for well-characterized samples of quartz and feldspar from different origins under our laboratory lighting conditions.
  
  references:
  Bailiff, I. K., & Poolton, N. R. J. (1991). Studies of charge transfer mechanisms in feldspars. International Journal of Radiation Applications and Instrumentation. Part D. Nuclear Tracks and Radiation Measurements, 18(1-2), 111-118.
  Sohbati, Reza & Murray, Andrew & Lindvold, Lars & Buylaert, Jan-Pieter & Jain, Mayank. (2017). Optimization of laboratory illumination in optical dating. Quaternary Geochonology. 39. 10.1016/j.quageo.2017.02.010.
  Spooner, N.A. (1993). The validity of optical dating based on feldspar. Unpublished DPhil thesis, University of Oxford, UK
  Spooner, N.A. (1994a). On the optical dating signal from quartz. Radiation Measurements, 23, Nos.2/3, 593-600.
  Spooner, N.A. (1994b). The anomalous fading of infrared-stimulated luminescence from feldspars. Radiation Measurements, 23, Nos.2/3, 625-632.
  Spooner, Nigel & Questiaux, Danielle & Aitken, M. (2000). The use of sodium lamps for low-intensity laboratory safelighting for optical dating. 18.
  
  Citation: https://doi.org/10.5194/gchron-2023-1-AC2
AC3: 'Comment on gchron-2023-1', Marine Frouin, 19 Apr 2023

On behalf of all co-authors, I would like to thank the reviewers for their thorough comments.

Citation: https://doi.org/10.5194/gchron-2023-1-AC3

Marine Frouin et al.

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Short summary

Here, we present the lighting setting implemented in the new Luminescence Dating Research Laboratory at Stony Brook University, USA. First, we performed spectral measurements on different light sources and filters. Then, we measured the loss of signal in quartz and feldspar samples when exposed to various light sources and durations. Finally, our lighting setting is suitable for a luminescence darkroom laboratory, it is simple, inexpensive to build, and durable.


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