Can 4k and 2,5k HMI's give the same light output?

[Eimulis]

I have acquired some old 2,5K and 4K HMI's.
When testing them I noticed that 2,5K LTM HMI gives the same light output as 4k Sirio HMI.

What could be the reason? Why 4k is not brighter?
Both lights has new Chinese bulbs now, but the output was the same with used Osram bulb on 4K. Can it be the bulb? Ballast? Or something else?

Here are the lights on full flood:


Here are the lights on full spot:

 

[Grug]

What are you measuring the light levels with? I'm assuming both lamps are fresnels? I'd expect approximately 1 stop more from a 4k over a 2.k at an equivalent distance/beam diameter.

However, sometimes in switchable 4k/2.5k fixtures, one of the bulb configurations will work less efficiently than the other due to the reflector being optimised for a particular bulb size.

 

[Eimulis]

They are the same distance from the wall in the photos, and 4k doesn't look like it's throwing more light.

Both ballasts are not switchable and 4k ballast is twice as bigger than 2,5k.

 

[Grug]

You're measuring the light by eye? That's silly and doesn't tell you what you need to know. Use a lightmeter, or a grey car with a waveform, and get some actual measurements.

 

[nyvz]

Dirty reflector? Misaligned bulb? Did you check power draw at the wall?

 

[Eimulis]

Dirty reflector? Misaligned bulb? Did you check power draw at the wall?

I've cleaned the reflector and glass.

How should be the bulb aligned?
How to check the power draw?

 

[puredrifting]

Grug's right. Light meter.

 

[robmneilson]

I wonder if it just has a 2.5k bulb installed? Surprised that it works without a switchable ballast though.

 

[Eimulis]

4k light has dedicated 4k ballast and 4k bulb, 2,5K the same.]

I've ordered light meter, time to start use it anyway

 

[puredrifting]

Only way to really tell what's going on. Every DP and photographer should own and know how to use a light meter. Let us know.