Planning cosy evenings away but wondering what the lights will take from your leisure battery? The good news is that working it out is simpler than it might sound.
Your lighting’s battery use comes down to three things: the power of each light, how many you switch on and how long you leave them running.
For example, lights drawing a combined 12 watts for four hours use 48 watt-hours of energy. On a nominal 12V system, that’s approximately 4 amp-hours from your leisure battery.
If those terms are new to you, don’t worry. We’ll explain them as we go, then work through an evening’s lighting using products from our BrightVans range.
Whether you’re fitting out a campervan or refreshing the lighting in a motorhome or caravan, the same calculations apply to a compatible 12V setup.
Watts, amps and amp-hours: what do they mean?
When you’re choosing 12V LED lighting, a few electrical terms keep cropping up. Here’s what you need to know.
| Term | What it tells you |
|---|---|
| Watts (W) | How much electrical power a light uses while it’s on. |
| Watt-hours (Wh) | How much energy it uses over time. A 3W light running for four hours uses 12Wh. |
| Volts (V) | The supply voltage. We’ll use 12V for the simple estimates in this guide. |
| Amps (A) | The electrical current a light draws while it’s running. |
| Amp-hours (Ah) | Current added up over time. You’ll also see this unit on leisure batteries to describe their capacity. |
Think of watts as the rate at which your light uses energy, and watt-hours as the total used by the end of the evening.
There’s one other useful distinction: watts measure power consumption; lumens measure light output. When choosing your lights, look at both. You want enough light for cooking, reading or relaxing, as well as a power draw that suits your setup.
How to calculate your lighting’s battery use
You don’t need to be an electrical expert to make a useful estimate. Start with the wattage shown in the light’s product specifications.
Step 1: Add up the power
Multiply the wattage of each fitting by the number you’ll be using.
Our Aneto Flush Light is rated at 2.2W, so two lights have a combined rated power of:
2 × 2.2W = 4.4W
Step 2: Allow for how long they’re on
Multiply that total by the hours of use.
If both lights run for four hours:
4.4W × 4 hours = 17.6Wh
That’s the estimated energy used by those two lights over the evening.
Step 3: Convert to amp-hours if you need to
To estimate amp-hours on a nominal 12V system, divide watt-hours by 12:
17.6Wh ÷ 12V = approximately 1.47Ah
You can use the same process for each part of your lighting setup, then add the results together.
Your handy formula:
Watts × number of lights × hours used = watt-hours
Watt-hours ÷ battery voltage = approximate amp-hours
We’re using 12V to keep the examples straightforward. Real leisure battery voltage varies, so these figures are planning estimates rather than exact measurements.
What does an evening of lighting use?
Let’s picture an evening away: lights on while you make dinner, a softer glow as you relax, then some reading before bed.
Here’s an illustrative setup using the published power ratings of three BrightVans products.
| Lighting | Combined rated power | Time on | Energy used |
|---|---|---|---|
| Two Aneto Flush Lights | 4.4W | 4 hours | 17.6Wh |
| One metre of Orion LED COB Strip Light White | 12W | 3 hours | 36Wh |
| One Nevis Reading Light, using its full listed 4W + 2W load | 6W | 2 hours | 12Wh |
| Total | 65.6Wh |
On a nominal 12V system:
65.6Wh ÷ 12V = approximately 5.5Ah for the evening
That gives you a useful starting point for your own lighting budget. Change the quantities and running times to match how you actually use your space. Include any additional fittings in areas such as the washroom or a separate bedroom.
This example assumes the lights run at their rated full output. It isn’t a measured test, and it excludes other appliances, additional controller consumption and wiring losses. Actual use will vary with voltage, brightness settings and your installation.
LED strip lights: remember to count the metres
LED strip lighting is a lovely way to brighten a worktop or add a welcoming glow around furniture. When calculating its power use, look carefully at whether the rating is per metre.
Our Orion LED COB Strip Light White is rated at 12W per metre. That means:
- One metre: 12W.
- Two metres: 24W.
- Five metres: 60W.
For example, two metres running at rated full output for three hours would use:
24W × 3 hours = 72Wh, or approximately 6Ah at 12V.
Use the length you’ve installed and powered in your calculation. If you’ve cut a longer roll down to one metre, calculate for that one metre.
LEDs are efficient, but a long strip can still make up a meaningful part of your lighting consumption. Checking the length and wattage now makes planning much easier.
What does that mean for your leisure battery?
Let’s return to our evening example of approximately 5.5Ah.
Compared with the nameplate capacity of a 100Ah battery, that’s around 5.5%, using our simplified 12V calculation. However, the capacity printed on your battery isn’t necessarily the amount you should plan to use.
Your usable capacity depends on the battery type, its manufacturer’s recommended discharge limits, its condition and temperature. You also need to account for how much charge it has when you park up.
Then there’s everything else sharing the battery. Depending on your setup, that could include your fridge, water pump, heating controls and device charging. Include the appliances that actually draw from your leisure battery in the operating mode you’re using.
The most useful approach is to build a daily energy budget for your whole setup, with lighting as one part of it.
If you know how much energy you have available specifically for lighting, you can estimate runtime:
Available energy for lighting (Wh) ÷ combined lighting power (W) = running hours
For example, an allowance of 120Wh would theoretically run a steady 12W lighting load for ten hours. Treat that as a planning figure, with room for real-world variation.
What changes when you’re on electric hook-up?
Your lights still use energy when you’re connected to electric hook-up. However, depending on your electrical system, a mains-powered charger or power supply can support the 12V loads and replenish the leisure battery.
That means the lighting consumption calculated here won’t necessarily equal the amount of charge lost from your battery while you’re plugged in. These battery-use estimates are most useful when you’re relying on stored energy without charging.
Five ways to use less power and keep your space cosy
A thoughtful lighting layout helps you put light where you need it.
1. Switch different areas separately
Separate controls for the kitchen, seating and sleeping areas let you choose which lights stay on as your evening changes.
2. Settle down with a reading light
Once dinner is cleared away, you may only need light beside your seat or bed. A fitting such as the Nevis Reading Light lets you direct light where you’re using it.
3. Dim compatible lights
Dimming can reduce power consumption while creating a softer evening atmosphere. All BrightVans lights can be dimmed. Check each product’s specifications for the controls or compatible dimmer it needs.
A 50% brightness setting doesn’t necessarily mean exactly 50% power consumption, so avoid assuming a precise saving without product data or a measurement.
4. Plan your strip lengths
Measure the areas you want to light up before buying and fitting LED strips. A carefully placed length under a cabinet may provide the light you need without running strip lighting around the whole interior.
5. Count charging separately
If your light includes a USB charging port, charging a phone uses additional energy. Don’t assume the LED wattage includes whatever you plug into that port.
Common questions about 12V LED lighting
How many amps do 12V LED lights draw?
For an estimate, divide power in watts by voltage. A 6W light draws approximately 0.5A at 12V. Where available, check the product’s listed current draw too.
Can I use BrightVans campervan lights in a motorhome or caravan?
Yes. Our 12V LED lighting is suitable for campervans, motorhomes and caravans with compatible electrical systems. Check each product’s voltage range, fitting dimensions and installation requirements when choosing lights for your interior.
Will LED lights drain my leisure battery overnight?
Any light left on uses energy. How much depends on its power and running time: a 3W light left on for eight hours uses 24Wh, or approximately 2Ah at 12V. Whether that fits your budget depends on your remaining usable battery capacity and other loads.
How long will LED lights run on a 100Ah leisure battery?
There isn’t one reliable answer from the battery label alone. You need to know its usable remaining capacity, the combined lighting load and what else is running. Use the calculation above with an energy allowance that suits your battery manufacturer’s guidance.
How can I check my actual lighting consumption?
A suitable battery monitor can help you see the change in battery draw when you switch your lights on. Keep other loads steady when comparing readings, and account for any charging from solar, electric hook-up or other sources.
Plan your lighting with confidence
Start with the spaces you want to light, check each product’s wattage and allow for how long you’ll use it. Those few steps will give you a much clearer picture of what your lighting needs from your leisure battery.
Whether you’re choosing Aneto Flush Lights for everyday lighting or Orion LED strip lighting for a softer glow, our product specifications help you put the numbers together.
For more inspiration, explore our guide to planning your lighting layout. You can create a space that feels comfortable, works for your adventures and has a lighting budget you understand.
