Does light affect mycelium?
Light is not essential in the mycelial growth period. However, in the period of initiation and growth of fruiting bodies, it is a decisive factor for obtaining a high yield of good quality.
While mycelium may not need light to grow, it would be a mistake to assume that mushroom fruiting bodies don't either. Regardless of whether it's natural or artificial, some lighting is thought to be necessary to complete the fruiting process and guide the growing direction of the fruiting body.
Light is an essential source in inducing the development of fruiting bodies which significantly affects the productivity of oyster mushrooms in both quantity and quality. LED has many advantages over current lightings and tends to be more effective for the cultivation of mushrooms.
The higher the inoculation rate or amount of spawn added to the substrate, the faster the mycelium will grow through the substrate.
Make sure that your environmental conditions are proper for the type of mushroom you are growing. Humidity, air exchange, light, and temperature are all important factors to keep a constant watch on. Growing mycelium generates its own heat.
Light controls important physiological and morphological responses in fungi. Fungi can sense near-ultraviolet, blue, green, red and far-red light using up to 11 photoreceptors and signalling cascades to control a large proportion of the genome and thereby adapt to environmental conditions.
The mycelium growth of PO and PC decreased when the ammonium chloride concentrations are over 0.09% and 0.05%, respectively.
Mycelium grew best during spawn-running when the temperature was kept at 75° F. (23·9° C.) During pre-cropping a temperature of 65° F. (18·3° C.)
Not Enough Moisture
Mycelium, the underground vegetative growth of a fungus, needs a moist environment to thrive and produce mushrooms. Mushrooms themselves are mainly water, so if you let the mycelium dry out or the humidity level get too low then nothing will happen.
Your plants will tell you if your lights are strong enough; weak, leggy plants indicate a need for more light. Most lights should be hung only a few inches from the plants.
Does fungi only grow in the dark?
Light: Fungi can only grow in the dark. For the most part, light does not play a role in how well fungi grow. There are some conditions where light is necessary for reproduction.
Light. Since mushrooms do not contain chlorophyll they do not require light or photosynthesis to grow. While the environment needs to be as dark as possible to for mushrooms to spawn, some light does not harm their growth.

Yeast extract is good for fungi and might make them stronger as it helps them grow.
If the mycelium fails to develop properly during the first two days, reduce the RH and CO2 more gradually. This will stimulate more mycelium growth. This helps, but only to a limited extent. In addition, if the casing soil still shows black during pinhead development, look between the clumps of casing for pinheads.
A substrate of fibrous, woody materials like cellulose, lignin and hemicelluloses is ideal. This type of substrate will provide plenty of carbon, the main food source for mycelium. The other main macronutrient required for growth and energy is nitrogen. The ideal substrate needs to contain one to two percent nitrogen.
Spread. A mycelium block can spread to any dirt block within one space above, one sideways, or three down. The mycelium needs light level 9+ above it, while the dirt needs light level 4+ above it, and must not be covered by any light-impeding block or any opaque block.
Oyster mushrooms have one the easiest and fastest mycelium growth, so I picked some up from an Asian supermarket and after slicing them up with some soaked cardboard I left them to grow happily*.
Growing mycelium should be kept in an ideal temperature range. For example, P. cubensis colonizes most rapidly between 75-80°F (24-27°C). Temperatures higher than this range may kill the mycelium and encourage growth of contaminants, and temperatures lower than this range may slow down colonization.
While it seems to be common knowledge that fungi have no need whatsoever for light, there are in fact many fungi that show a phototropic response. The zygomycete Pilobolus is well-known for “throwing” its “hats” in the direction of light and away from the dung upon which it grows.
All fungi that are photoresponsive appear to be sensitive to light at the blue to near-UV-A (~400–495 nm) range. Several classes of blue light receptors have been identified in fungi and will be briefly discussed; starting with the most well understood fungal photoreceptor class, the White Collars.
Does fungi grow in light?
Unlike plants, mushrooms do not require photosynthesis for growth. Therefore, many fungi species are cultivated in dark and cool environments, without intense exposure to sources of ultraviolet light (Simon, 2013).
In conclusion, it can be seen that contrary to some beliefs, fungal cells are indeed killed by the action of blue light alone, and this effect may have both medical and agricultural applications.