want to light a hall of 300 people
 

the question is....if I can do it on the cheap for 2 twin head lights for £50.....

Telescopic Tripod 500W Site Light - Screwfix.com, Where the Trade Buys

then why would I pay £685 for these 2 lights?

PhotonBeard PhotonBeam 2 x 800W Kit ( Hard Case ) - Proactive

For a one time use as a flood light there'd be no advantage to get the more expensive one.

Portability and focusability would be the advantage of the more expensive one. But Halogen watts are halogen watts.

Hall of three hundred people - Neither of these is up to it. You're going to need a lot more than two lights of 500 or 800w each to light a room that holds that many people.

I did an auditorium about that size one time. I think we used 10 or 12 Lowel 1,000 watt lights mounted along the ceiling, and then about half a dozen 1K fresnels. It wasn't wonderful but was adequate.

The cheap site floods are pretty crude, the stands don't go very high, they are 'blam' type lighting, exactly what you'd expect for a work light. The redheads are more even, don't have nasty dim bits from protective wire work in front of them, just a fine even mesh. The redheads are also brighter. That said, a redhead each side or a worklight each side is a pretty nasty way of trying to light a big crowd. Neither will throw very far and if the room is big the back will be dark, unless you can get them very high up. Mind you, if you don't get them high up, they'll blind the audience anyway. I do theatre shows where sometimes the audience take part, and have to be put up on screens so people can see them, and I light them with a minimum of 4000W from 4 sources, high up. This is just enough, and the cameras work lens wide open and pictures are very flat.

I am know thinking of making my own light using say 6-9 bio-bulbs
BIO BULB
they're full daylight spectrum and 3 times brighter than a normal bulb and low energy and heat and i will put a switch on each individual bulb.

I wouldn't bother - you've been fed some kind of accurate, but misleading info. Lumens isn't a very useful method of measurement, because it assumes light goes everywhere, not in a single direction, as in the kind of job you're talking about.


The ad says
"The BioBulb 100w (using 25w) bulb issues a massive 1750 lumens". Wow, sounds a lot doesn't it?
The 800W redhead lamps are short tubular things, and they produce 20000 lumens, so you need a hell of a lot of the energy saving lamps to equal the light output of just a single proper light.

These energy saving lamps sadly, are well know for being ....... dim! Despite the specifications, swapping out incandescent lamps for low energy lamps is always met with comments about brightness.

You can get cheap Chinese redhead kits on ebay for just over 200 quid, complete with stands, cases and lamps. They're not as tough as the usual Redheads which are more than this for just one, but they are bright!

Your biobulb idea could work if you up the quantity, and then make four of them to cover the room. In fact, my guess is that the light would also be quite soft, coming from a wider area. A silver or white background would also concentrate and make the most of the light. Downside being weight, making a solid stand critical.

Just to put lumens into perspective, a typical 5 foot 40W flurorecent tube has a light output of around 3500 lumens, and a typical home style 60W bulb runs in at around 500/600 lumens - so these biobulbs do have some advantages.

One real issue is colour - they often look a little weird to the camera.

In Europe we're measuring light output in Lux and before that we used foot candles, which make light levels at certain distances easy to compare from fixtures that can alter their beamwidth. As the Lumen is a measure of the perceived power of light, it is difficult to compare without considering the kind of bulb. The length of the tube emitting the light has a big impact on the measurement. A small envelope bulb vs a 5 foot flu tube - makes the measurements make sense, but we all know how flu tubes often make a room look brighter, because they are quite long. A very complex subject and each result has to be put into context to make a decision on which is really brighter - or might seem to be?