Lighting is one of the less discussed topics in invertebrate keeping, partly because the answer for most species is straightforward: they do not need special lighting. Unlike reptiles, where UVB provision can mean the difference between health and metabolic bone disease, the vast majority of invertebrates in the UK hobby do perfectly well under ambient room light or a simple day/night cycle. But "they don't need UVB" does not mean lighting is irrelevant.
Do invertebrates need light?
They need a light cycle. Most invertebrates have circadian rhythms driven by light and dark periods. Isopods are more active at night, hiding during the day and foraging in darkness. Jumping spiders are diurnal hunters that rely on their exceptional eyesight, which means they need light to function normally. Millipedes tend to be crepuscular or nocturnal, retreating to dark, damp spaces during daylight hours.
A consistent photoperiod of roughly 12 hours light and 12 hours dark works for most tropical species. For species from temperate regions, seasonal variation in day length may influence breeding behaviour, though this is less studied in captive invertebrate populations.
The light does not need to come from a dedicated lamp. A room with windows provides a natural light cycle. If your collection is in a room without natural light, like a cupboard or basement, a simple LED on a timer gives your animals the day/night cycle they need.
UVB: do invertebrates need it?
For reptiles, UVB is often non-negotiable because it drives vitamin D3 synthesis, which enables calcium metabolism. Without UVB (or dietary D3 supplementation), reptiles develop metabolic bone disease.
Invertebrates have a fundamentally different relationship with calcium and vitamin D. Isopods, for example, obtain calcium directly from dietary sources like cuttlebone and eggshell, and their calcium metabolism does not depend on UVB exposure the way a reptile's does. Millipedes similarly absorb calcium from their substrate and food. Beetle exoskeletons harden through a sclerotisation process involving proteins and chitin, not calcium deposition in the way vertebrate bones work.
So no, your isopods do not need a UVB bulb. Neither do your millipedes, beetles, or mantids. This is one area where reptile husbandry advice genuinely does not transfer to invertebrates. Spending money on UVB for an isopod colony is unnecessary.
When lighting does matter
Jumping spiders
This is the one group where lighting makes a real difference to the animal's quality of life. Jumping spiders (family Salticidae) are visual predators with some of the best eyesight in the invertebrate world. Their anterior median eyes have tube-shaped retinae that can resolve detail at remarkable distances for their size. They rely on this vision to locate, stalk, and pounce on prey.
A jumping spider in a dark enclosure cannot hunt properly. Ambient room light is usually sufficient, but if the enclosure is in a dim spot, a small LED desk lamp or an LED strip provides enough illumination. Avoid placing the enclosure in direct sunlight, though, as the temperature inside a small glass or plastic enclosure in direct sun can climb rapidly and kill the spider.
Live plants in bioactive setups
If you grow live plants in your terrariums, they need light to photosynthesise. Low-light tropical plants like pothos, ferns, and mosses can survive under ambient room light near a window, but a small grow light makes a noticeable difference in plant health. A 6500K LED strip or a small clip-on grow light running for 8-10 hours per day keeps plants green and growing without producing excessive heat.
Be cautious with heat output from lights. Incandescent bulbs and some older grow lights produce significant heat, which can raise the temperature inside a small enclosure beyond what your invertebrates tolerate. LEDs are cooler and more energy-efficient for this purpose.
Display enclosures
If you keep invertebrates in a display tank, like a nicely planted terrarium on a shelf, lighting obviously matters for aesthetics. A warm-white or daylight LED strip along the top of the enclosure shows off the animals and plants without generating much heat. It also provides that day/night cycle if you put it on a timer.
What to avoid
Direct sunlight on enclosures. This is the most common lighting-related mistake. A glass or plastic enclosure in a sunny window acts like a greenhouse. Internal temperatures can exceed 35-40C within minutes on a warm day, which is lethal for most invertebrate species. Even on cool days, direct sun through glass creates hotspots.
Leaving lights on 24/7. Constant light stresses nocturnal and crepuscular species. Isopods exposed to permanent light will hide constantly and may breed less. A timer that provides a regular day/night cycle costs a few pounds and solves this.
High-wattage heat lamps. These are designed for reptile basking spots and produce intense, focused heat. They will dry out invertebrate enclosures rapidly and can overheat small containers. If you need heat, use a heat mat or ceramic emitter. If you need light, use an LED.
My setup
Most of my collection sits on shelving in a room with a north-facing window. They get ambient daylight during the day and darkness at night. No additional lighting is needed for the isopods, millipedes, or beetle larvae since they spend most of their time buried in substrate anyway.
My jumping spider enclosures sit on a desk near the window where they get good ambient light. On grey winter days I switch on a desk lamp nearby. The spiders are visibly more active and hunt more confidently when the light is decent.
The one display terrarium I have, a planted isopod setup, has a cheap LED strip on a timer set for 10 hours. The plants stay healthy, the isopods hide during the lit hours and come out when it switches off, and the whole thing looks good on the shelf. The LED strip was about twelve pounds and the timer was three. Not exactly a major investment.
For most invertebrate species, natural room light and a regular day/night cycle are all you need. If you have budget to spare, spend it on substrate or heating before lighting.