I’ve been trying different searches but everything I find just says “sunlight”. Since sunlight consists of multiple parts such as UV, Infrared and the normal visible spectrum, I’m curious which part is actually responsible for photosynthesis to occur? On that note, depending on what part of the light, would it still grow with an LED, black light, etc.?
Awesome, so if I’m reading that right UV can contribute to growth, and IR doesn’t contribute much at all. The blue and red end of the visible spectrum encourages growth, however it can pretty much occur at any visible wavelength, just not as efficient as the bands listed on the image.
Blue and red are the biggest drivers for photosynthesis, but other wavelengths have effects on the plants as well. For example, far red light (infrared) has a huge influence on flowering and stem elongation in many plants. They really rely on light for a lot of cues for regulation.
Edit: words
That chart is a good starting point, but it doesn’t tell the whole story. It only shows the absorption spectrum for Chlorophyll A, which is a key pigment for photosynthesis in all plant species, but there is also Chlorophyll B, and there are numerous other so called accessory pigments (beta carotinoids are the most common examples), that can work in conjunction with chlorophyll in a photosystem to collect light of different wavelengths. Algae in particular show a greater diversity of accessory pigments. They have evolved use light at different depths below the water surface, where it reaches them with a different spectrum, because water itself absorbs part of it. Have a look at red algae and brown algae, for example.
So if you want to grow algae in a controlled environment, you should do some research about the particular absorption preferences of the species you’d like to grow.