{"id":1225,"date":"2026-05-12T19:25:28","date_gmt":"2026-05-12T19:25:28","guid":{"rendered":"https:\/\/blogs.dickinson.edu\/allarm\/?p=1225"},"modified":"2026-05-12T19:25:28","modified_gmt":"2026-05-12T19:25:28","slug":"a-nitrate-experiment-the-effect-of-light-on-color","status":"publish","type":"post","link":"https:\/\/blogs.dickinson.edu\/allarm\/a-nitrate-experiment-the-effect-of-light-on-color\/","title":{"rendered":"A Nitrate Experiment: The Effect of Light on Color"},"content":{"rendered":"

Which\u00a0light environment\u00a0should we\u00a0test for nitrate in?\u00a0<\/span><\/b>\u00a0<\/span><\/p>\n

Nitrate\u00a0is an important\u00a0indicator\u00a0of stream health.\u00a0At ALLARM,\u00a0the\u00a0LaMotte Nitrate-Nitrogen Tablet Kit is used to measure the concentration (mg\/L) of nitrate-nitrogen in water.\u00a0Nitrate-<\/span>\u00a0<\/span>nitrogen\u00a0(NO<\/span>3-<\/span>N)\u00a0measures\u00a0the amount of nitrogen in the nitrate\u00a0ion (NO<\/span>3-<\/span>)\u00a0(1).\u00a0Nitrate\u00a0ions\u00a0are\u00a0a major form of\u00a0dissolved\u00a0nitrogen in water\u00a0due to high solubility\u00a0(2).\u00a0Although nitrate\u00a0is a necessary nutrient for plants, too much nitrogen in water can cause problems such as overgrowth of\u00a0SAVs\u00a0(submerged\u00a0aquatic vegetation),\u00a0plant die-off and plant decomposition that can result in a reduction in dissolved oxygen. These make it harder for organisms to survive in the stream. With the LaMotte kit, a color comparison of the samples and concentration scale in the kit is used to determine the nitrate-nitrogen value (Photo 1).<\/span><\/p>\n

\"\"

Photo 1: Color comparison with LaMotte Nitrate-Nitrogen kit.<\/p><\/div>\n

The\u00a0LaMotte Nitrate-Nitrogen Table Kit\u00a0is an\u00a0easy kit\u00a0that makes nitrate testing\u00a0more\u00a0accessible. However,\u00a0since it uses a color scale,\u00a0it is\u00a0a\u00a0very subjective way of\u00a0determining\u00a0concentration.\u00a0<\/span>Each person perceives the color differently when comparing the sample color and the color on the slide,\u00a0possibly\u00a0leading\u00a0to the inaccurate value<\/span>.\u00a0<\/span>Additionally, the color of the sample and the slide look different under different light environments, and certain concentration ranges on the bar are lighter and therefore more challenging to determine the value. In the past, when comparing nitrate values with the HACH TNT 835 method, which is a more high-resolution spectrophotometer method, we found values measured with TNT were an average of 1.2 mg\/L lower than the kit. This example highlights the challenges of using the kit. This experiment was designed to understand how different light environments affect nitrate readings and find the best light environment to minimize error in reading the values. <\/span>\u00a0<\/span><\/p>\n

Methods\u00a0<\/span><\/b>\u00a0<\/span><\/p>\n

Table 1:\u00a0Different\u00a0light\u00a0environments used in this\u00a0experiment.<\/span>\u00a0<\/span><\/p>\n

\"\"

A. In front of the office window.
B. Natural light outside.
C. In the middle of the office (Access to natural light but not facing it).
D. Inside the lab room (No access to natural light, access to artificial light but not facing it directly).
E. Artificial Lighting (Facing directly to artificial light in the lab).
F. White Paper \/ Wall (In the lab, on the table, white paper on background).<\/p><\/div>\n

Table 2:\u00a0<\/span>Weather\u00a0<\/span>condition\u00a0<\/span>during<\/span>\u00a0the<\/span>\u00a0experiment<\/span>.<\/span><\/p>\n

\"\"<\/p>\n

Table 3: <\/span>Nitrate s<\/span>tandards used in the experiment<\/span>.<\/span><\/p>\n

\"\"<\/p>\n

In this experiment, I followed the same protocol that our volunteer monitors use for nitrate testing using the LaMotte Nitrate-Nitrogen Tablet Kit. Three different concentration standards were used to compare the measured value and actual value (Table 3). Five ALLARM members including full-time staff and student watershed coordinators were involved in data collection. During each trial, the values were measured on the same day, at around the same time, and at the same locations. To determine the accuracy of each light environment, I compared the value measured with the kit to the value of the standard used in the experiment. <\/span>\u00a0<\/span><\/p>\n

After collecting data, I analyzed the difference between the known standards values and the values read from the kit and considered tendency of reading colors in each environment. I categorized them into four datasets that used different variables and visualized them on Excel. The first dataset assessed different concentration standards, the second weather, the third different light environments, and the fourth individual testers.<\/span>\u00a0<\/span><\/p>\n

Results\u00a0<\/span><\/b>\u00a0<\/span><\/p>\n

Table 4:\u00a0Three different concentration\u00a0standards\u00a0used\u00a0in the\u00a0experiment.<\/span>\u00a0<\/span><\/p>\n

\"\"<\/p>\n

Higher concentration\u00a0<\/span>standard<\/span>s<\/span>\u00a0<\/span>such as<\/span>\u00a0<\/span>6.0\u00a0<\/span>mg<\/span>\/L\u00a0<\/span>had a lower\u00a0<\/span>percent<\/span>\u00a0error\u00a0<\/span>of\u00a0<\/span>5.21<\/span>%\u00a0<\/span>and 21.39<\/span>%<\/span>\u00a0compared to<\/span>\u00a0the<\/span>\u00a0lower\u00a0<\/span>concentration<\/span>\u00a0<\/span>standards\u00a0<\/span>(0.5<\/span>\u00a0and<\/span>\u00a02.0<\/span>\u00a0mg\/L<\/span>)\u00a0<\/span>which had\u00a0<\/span>percent<\/span>\u00a0error<\/span>s<\/span>\u00a0of 46.<\/span>88<\/span>%<\/span>\u00a0and 58.4<\/span>%<\/span>,<\/span>\u00a0<\/span>respectively<\/span>\u00a0(Table 4)<\/span>.\u00a0<\/span>For 0.5<\/span>\u00a0mg\/L<\/span>,\u00a0<\/span>the average value was lower than the actual value<\/span>.<\/span><\/p>\n

\"\"

Figure 1: The difference in average value under different weather conditions (standard 6.0 mg\/L).<\/p><\/div>\n

When using the same standard under different weather\u00a0conditions\u00a0(sunny and cloudy), the average value differed by\u00a0about 1.6\u00a0mg\/L. The values tended to be\u00a0read\u00a0higher\u00a0by approximately 1.1\u00a0mg\/L\u00a0on\u00a0average\u00a0on\u00a0cloudy days.\u00a0When\u00a0testing nitrate values\u00a0outside\u00a0on\u00a0a cloudy day,\u00a0the average value was\u00a01.6\u00a0mg\/L\u00a0higher\u00a0than\u00a0the actual value.\u00a0In contrast, the\u00a0results were\u00a0close\u00a0to the actual value\u00a0when testing outside\u00a0on\u00a0a sunny day,\u00a0being\u00a0lower\u00a0by only 0.4\u00a0mg\/L\u00a0on\u00a0average\u00a0(Figure 1).\u00a0<\/span>\u00a0<\/span><\/p>\n

Table 5:\u00a0The\u00a0percent\u00a0error of different light environments and weather conditions.<\/span><\/p>\n

\"\"<\/p>\n

Reading standards on a sunny day in front of the office window had the lowest percent error, while reading inside using white paper has the highest percent error.\u00a0<\/span>Overall,<\/span>\u00a0<\/span>though, percent<\/span>\u00a0error was\u00a0<\/span>low<\/span>. On a cloudy day, in front of the office window, inside the lab room and facing artificial lighting have the lowest percent error for that weather\u00a0<\/span>condition but<\/span>\u00a0are still much higher percent errors than measurements on a sunny day. On average, the\u00a0<\/span>percent<\/span>\u00a0error on the sunny day was 5.9% while percent error on cloudy day was 42.2%.\u00a0<\/span><\/span>\u00a0<\/span><\/p>\n

\"\"

Figure 2: Results from testing standard 0.5 mg\/L outside with light passing through the kit.<\/p><\/div>\n

 <\/p>\n

\"\"

Figure 3: Results from testing standard 0.5 mg\/L inside without light passing through the kit.<\/p><\/div>\n

T<\/span>he same standard\u00a0<\/span>(<\/span>0.5<\/span>\u00a0mg\/L<\/span>)<\/span>\u00a0<\/span>was tested\u00a0<\/span>on the same day but\u00a0<\/span>in\u00a0<\/span>two<\/span>\u00a0different\u00a0<\/span>light environments<\/span>\u00a0where\u00a0<\/span>the first environment\u00a0<\/span>had\u00a0<\/span>a lot of light coming throug<\/span>h the kit and the second environment did not have\u00a0<\/span>enough lighting<\/span>. Outside<\/span>\u00a0where there was\u00a0<\/span>more<\/span>\u00a0<\/span>natural light<\/span>, three out of five<\/span>\u00a0testers\u00a0<\/span>read<\/span>\u00a0the\u00a0<\/span>stand<\/span>a<\/span>rd\u00a0<\/span>accurate<\/span>\u00a0value<\/span>\u00a0(Figure 2)<\/span><\/span>.\u00a0<\/span>When the kit was performed inside where there was no direct light passing through, o<\/span>nly one tester\u00a0<\/span>read the\u00a0<\/span>standard<\/span>\u00a0<\/span>value,<\/span> and the color was <\/span>perceived<\/span>\u00a0<\/span>lighter<\/span>\u00a0(Figure 3)<\/span>.\u00a0<\/span>Photo 2 shows the\u00a0<\/span>clear difference in the color of the same standard under\u00a0<\/span>different<\/span>\u00a0light environments.<\/span>\u00a0<\/span>When the test was performed outside, the average value was 0.2 mg\/L lower than the actual when\u00a0<\/span>it was performed inside and in front of white\u00a0<\/span>paper,<\/span>\u00a0the average value was 0.<\/span>35 mg\/L lower.\u00a0<\/span><\/span>\u00a0<\/span><\/p>\n

\"\"

Photo 2: The color difference of the same standard in different light environments.<\/p><\/div>\n

\"\"

Figure 4: Data collected by five individuals in front of the window with the 6.0 mg\/L standard.<\/p><\/div>\n

The values varied\u00a0widely in\u00a0all standards and locations.\u00a0Especially,\u00a0for higher concentrations, the\u00a0range\u00a0between highest and lowest reading\u00a0was\u00a0\u00b1\u00a03.5\u00a0mg\/L\u00a0(Figure 4).\u00a0<\/span>\u00a0<\/span><\/p>\n

Discussion<\/span><\/b>\u00a0<\/span><\/p>\n

From this result, ALLARM can suggest several tips to measure the most accurate value when using the nitrate kit. Since many factors affect color reading, it is hard to conclude this experiment with one suggestion. <\/span>\u00a0<\/span><\/p>\n

The best light environment overall\u00a0was\u00a0in front of the window, which\u00a0had\u00a0the most\u00a0accurate\u00a0readings consistently\u00a0both\u00a0on sunny and cloudy days.\u00a0<\/span>\u00a0<\/span><\/p>\n

It is important to keep in mind that\u00a0the octa-slide\u2019s\u00a00.0 \u2013 2.0 mg\/L\u00a0range\u00a0that is\u00a0harder to distinguish\u00a0the color and read the value\u00a0(photo 3).\u00a0When your\u00a0sample\u00a0has\u00a0a low\u00a0nitrate value, it is important to have light\u00a0traveling\u00a0throu<\/span>gh the sample\u00a0and Octa-slide\u00a0from behind\u00a0(Figure 2 and 3).<\/span><\/p>\n

\"\"

Photo 3: Octa-slide.<\/p><\/div>\n

From table 4, the\u00a0percent\u00a0error suggested that higher concentrations have higher accuracy<\/span>\u00a0<\/span>regardless of the light environment. Additionally, higher concentration standards were easier to read accurately, while lower concentration standards like 2.0 and 0.5 were often perceived darker for all locations and were off from the actual value by around 50%.<\/span>\u00a0<\/span><\/p>\n

The experiment was supposed to be held on the same day with same people; however, it ended up being done on two different days under different weather. That also suggested that the weather affects how we perceive the color. If possible, the nitrate kit should be performed outside with natural light when it is sunny. However, it won\u2019t always be sunny on sample collection days. We would recommend testing nitrate even if it is a cloudy day or under unideal conditions since nitrate is a time sensitive parameter and needs to be done as soon as the sample is collected. In that case, the second-best option is to test inside a building where enough lighting is provided, such as in front of a big window or facing artificial light. This experiment also showed the importance of meta data such as weather on the day of collection along with your values.<\/span>\u00a0<\/span><\/p>\n

The results were surprising because it shows how different values can be with the same standard depending on each tester.<\/span>\u00a0<\/span><\/b>Everyone has unique tendencies. For example, one tester tended to see color much darker than it is almost all the time. Others did not perceive the color differently in any environment. It may be helpful to ask several people as a second check or to take a picture of the bar and colored samples next to each other, so you have reference later.\u00a0 <\/span>\u00a0<\/span><\/p>\n

This experiment gave us helpful insights on how to minimize human error while reading the kit and maintain the accuracy of the nitrate kits. Next time, this experiment could be carried out with a larger group and variety of testers. More standards can lead to better analysis, less bias and demonstrate wide variation in reading. During the experiment, Jill Ariola, ALLARM\u2019s Staff Scientist, suggested a new way of comparing colors. She recommends putting the samples and Octa-slide 2 bar next to each other without using the black case (photo 4, 5). Comparing the sample colors that are next to the bar may be easier to see the difference than using a black case. This method can be used in further experiments.<\/span><\/p>\n

\"\"

Photo 4, 5: Suggested ways to make color comparison easier.<\/p><\/div>\n

This experiment supports how subjective the value measured with the kit can be. By analyzing them carefully, we\u00a0<\/span>found<\/span>\u00a0ways to\u00a0<\/span>increase\u00a0<\/span>accuracy based<\/span>\u00a0on\u00a0<\/span>light\u00a0<\/span>and weather conditions<\/span>\u00a0for testing<\/span>.\u00a0<\/span><\/p>\n

References\u00a0\u00a0<\/span><\/b>\u00a0<\/span><\/p>\n

    \n
  1. Nitrate nitrogen (NO3-N) or nitrate (NO3-) \u2013 Know the Difference! | Announce | University of Nebraska-Lincoln<\/span><\/a>\u00a0<\/span>\u00a0<\/span><\/li>\n
  2. Nitrates_Drinking_Water.pdf<\/span><\/a>\u00a0<\/span><\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"

    Which\u00a0light environment\u00a0should we\u00a0test for nitrate in?\u00a0\u00a0 Nitrate\u00a0is an important\u00a0indicator\u00a0of stream health.\u00a0At ALLARM,\u00a0the\u00a0LaMotte Nitrate-Nitrogen Tablet Kit is used to measure the concentration (mg\/L) of nitrate-nitrogen in water.\u00a0Nitrate-\u00a0nitrogen\u00a0(NO3-N)\u00a0measures\u00a0the amount of nitrogen in the nitrate\u00a0ion (NO3-)\u00a0(1).\u00a0Nitrate\u00a0ions\u00a0are\u00a0a major form of\u00a0dissolved\u00a0nitrogen in water\u00a0due to high solubility\u00a0(2).\u00a0Although nitrate\u00a0is a necessary nutrient for plants, too much nitrogen in water can cause problems […]<\/p>\n","protected":false},"author":5797,"featured_media":1236,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-1225","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized"],"acf":[],"_links":{"self":[{"href":"https:\/\/blogs.dickinson.edu\/allarm\/wp-json\/wp\/v2\/posts\/1225","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.dickinson.edu\/allarm\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.dickinson.edu\/allarm\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.dickinson.edu\/allarm\/wp-json\/wp\/v2\/users\/5797"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.dickinson.edu\/allarm\/wp-json\/wp\/v2\/comments?post=1225"}],"version-history":[{"count":5,"href":"https:\/\/blogs.dickinson.edu\/allarm\/wp-json\/wp\/v2\/posts\/1225\/revisions"}],"predecessor-version":[{"id":1262,"href":"https:\/\/blogs.dickinson.edu\/allarm\/wp-json\/wp\/v2\/posts\/1225\/revisions\/1262"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.dickinson.edu\/allarm\/wp-json\/wp\/v2\/media\/1236"}],"wp:attachment":[{"href":"https:\/\/blogs.dickinson.edu\/allarm\/wp-json\/wp\/v2\/media?parent=1225"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.dickinson.edu\/allarm\/wp-json\/wp\/v2\/categories?post=1225"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.dickinson.edu\/allarm\/wp-json\/wp\/v2\/tags?post=1225"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}