LED light
Today I finally received the TC420 Programmable Time Controller unit which I ordered on eBay at the beginning of November. The unit serves to control the intensity of up to 5 LED channels. It allows definition of a table with the times and the particular LED channels intensities. The unit works with the DC voltage 12–24 V and current of up to 4 A per channel. Its price is approximatelly 600 Kč (US$ 25).
Some time ago, I received 5-meter waterproof RGBW LED strip that I had ordered on eBay for approx. 800 Kč (US$ 35). The white channel of these LEDs is of neutral 4000 K white light. If we compose the three colors red, green, and blue, the resulting spectre will have three extremes with these colors. In these points the intensities will have their maximums. To better span the spectre, the white channel is added to amplify the intensities of the colors lying in between these extremes – mainly yellow and cyan. The power of the 5-m long strip is 72 W. To reduce losses on the conductors I ordered a 24-volt strip which comprehends the current of 3 A at the maximum power.
To cool down the LED strip, it is necessary to stick it on a metal profile, the most indicated is the alluminium, which is light and dissipates the heat well. I ordered alluminium profiles of 40 x 20 x 2 mm with the weight of 0.6 kg/m from the ALMS company in Brno Modřice - the lengths of 32 cm, 42cm and 2 pieces of 52 cm. The total price was 165 Kč (US$ 7). It was necessary to drill holes in the profiles and then make thread in them. I fitted the profiles with screws to the plastic aquarium hoods. On one profile, I stuck 3 strips in parallel. I had to connect them with wires and isolate them in the ends.
The front and rear parts of the aquarium hood are independent and both have a 5-pin connector to be easily disconectable. Two 5-wire ribbon cables are led from the programmable unit to the front and rear part of the aquarium hood.
To be able to imitate the sunlight profile, it was necessary to measure the sun color and intensity. I used the monitor calibration probe x-rite i1Display to measure the sun’s profile. I located the probe near the window to measure the sun from noon to sunset with the period of 15 minuts; at sunset, more often. The sun sets at 4 pm in December, so it didn’t take much time. There was a slight problem when a cloud appeared right before sunset and distorted the measurement a bit. I recorded the values into an Excel sheet, it means the time, intensity and color in the x-y coordinates.
Now it was necessary to set up the aquarium light. I took the entire hood to a dark room and put it on chairs. I located the probe below the light. The original light with two T5 tubes (56 W in total) had 1700 lx and the color x = 0.296, y = 0.339. When I turned on just the white channel of the new LED ligtht (power of 18 w), the intensity was 2500 lx. When I turned on all four channels together (where the power supply was rated to 65 W only), the intensity was 6500 lx. I decided to set up the peak corresponding to the noon time to 4500 lx.
I recalculated the times in the table to match the day time of 12 h. I set up the noon instant to 2 pm that resulted with the reasonable illumination between 8 am – 8 pm. For each point of time I applied combination of four values PWM 0 – 100 % such the intensity and color coordinations of the light match the values in the table. The TC420 unit allows linear interpolation of the values between two times. At the very low intensities it was necessary to make step changes of the values without interpolation because the unit can change the values by 1 percent. This may cause the color drifting when the values are very low. For the moment before sunrise and after sunset I used weak white colors via the purple; the margin values before the off and after the on time were 1 % of the blue color.
I put the hood with the new light back on the aquarium.Concerning the original light, I only removed the tubes leaving the inverter untouched. The aquarium coloration is now more vivid and natural. What I was supprised of, that at around noon time air bubbles started to come out from the leaves of the plants.
